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5.7L overheating only at idle..........where to turn?

clbme

Member
Good evening,

I have a 2001 Crusader 5.7L TBI. Motor has a closed cooling system cooled by a raw water pump/heat exchanger. I have been working on the engine using a garden hose, however, it overheats when we tried to take the boat out on a fresh water lake.


I bought it used, history reported to have low hours for what it's worth. The motor overheats only at idle (approx 650 rpm factory set). If I bump it up just a bit to 800+ rpm the motor cools right down to 160-170 on the gauge. To date I have chased the problem by doing the following:

- Rebuilding the raw water pump. New cam, new impeller, new seal. It does not leak and the bearing appear to be fine when tested by feel. Neither the inside of the pump nor the cover are worn.

- Flushing the engine and raw water circuit entirely. I've back-flushed all areas of the motor and cooling system that I am aware of. I am able to put a full-power garden hose into the the elbows w/o any back flow, the same is true for the exhaust manifolds. The heat exchanger tubes are clear. The U-cooler is clear. I pulled the drain plugs on the block and flushed the engine completely with fresh water. By putting water into the hose directly at the u-cooler I get full, clear flow at both elbows.

- I changed out all of the closed system cooling hoses. The original ones did have a "crunch" to the them and I did flush a lot of grit out of them when I flushed it.

- Installed a new water pump.

- Checked the thermostat and it is operating properly. I also tried it w/o it installed. It's a 170 degree thermostat.

- Completely drained the closed system and flushed it as well. Filled the system with new coolant.

- Bought a Lisle spill-free coolant "burping" funnel and have removed all of the air from the system as as far as I can tell. Although the engine still appears to need two or three quarts approximately of coolant to meet the 23 qts listed in the manual.

- Replaced the heat exchanger cap.



During operation- even when the temp is rising/hot, the exhaust elbows are cool to the touch as are all of the raw water hoses.


*The one issue I do seem to have is that the exhaust manifolds are hot. Should they be cool to the touch as the elbows are? If so, is it possible they need to be replaced even if I can flush water through them without any seeming obstruction?

Would a faulty temp gauge read like this only at idle? This is the one thing I have not changed out yet.

I did check the engine over with a IR temp gun and found no hot spots except for the exhaust manifold, however, I don't think they matched the 200 and rising temp. I always shut it down when it hits 200 degrees. I will double-check this tomorrow and report my findings.




I'm at a loss and would be grateful for any advice.

Thanks,


Christian
 
It sounds like you have covered most of the obvious possible solutions, although the fact that you only see the problem at low rpm means most of this stuff was good to check but really could not only appear as an issue at idle.

First, I would make sure the belts are tight, as they could be slipping and the issue could show itself more at low rpm.

Is the low rpm overheat only at startup, or do you also see it after higher speed running and then it appears after you idle down? I ask this because I believe your cooling system has a bypass that cuts out the heat exchanger until the thermostat sees 170 degrees. But the temp sender is well before that point and perhaps sees 200 degrees before the thermostat opens. I would try just letting it go beyond 200 at idle and see if the thermostat opens and sucks the temps back down. Maybe you just think you have a problem but the behavior is normal.

Be aware that your engine has a temp sender (that sends the temperature to the gauge) and a temp sensor that sends a temperature (hopefully the same) to the engine control module. At least one and maybe both are mounted near the front of the intake manifold. But it is unlikely if sender or gauge is bad it will only show up at low rpm (unless it is some sort of electrical problem). Still, if you shine your IR gun next to the sender it should read the same as your gauge.

The engine module should trigger an audible alarm if it thinks the temps are too high (I think that is usually around 210). If you do get an over temp give the engine 20 minutes or so to cool down before restart. Fresh coolant on a hot head/block is what cracks them.

I don't recall what the correct temp is on the exhaust manifold but I think on your engine they are in the cooling circuit after the head/block but before the thermostat/heat exchanger (or bypass) so they should be the hottest thing there. They always are hotter than the risers. So that makes sense but that also argues that the thermostat should see 170 pretty quickly in the warmup cycle which maybe kinda kills my earlier possible theory.

Often the biggest cooling issue, that shows up in different ways (in my limited experience), is air in the system. I do a lot of hose squeezing to burp the system when I fill it. But you need several heat/cool cycles to get the air out. Is the system sucking coolant back in when the engine cools? If not, you have a leak, usually the cap seat, the cap (you changed yours) or the hose to the overflow. At heat up the coolant expands and (hopefully) pushes some the the trapped air out. After heat up, nothing happens so running all day won't improve anything. On cool down a suction is created and you want it pulling fluid in, not air. Several cycles are needed to get success.

Good luck,
CaboJohn
 
Christian, I have to agree with John. It is rare to see an over-heat at low RPM and yet not above that.

CoboJohn said:
Is the low rpm overheat only at startup, or do you also see it after higher speed running and then it appears after you idle down?
1.... I ask this because I believe your cooling system has a bypass that cuts out the heat exchanger until the thermostat sees 170 degrees. But the temp sender is well before that point and perhaps sees 200 degrees before the thermostat opens.
2.... I would try just letting it go beyond 200 at idle and see if the thermostat opens and sucks the temps back down. Maybe you just think you have a problem but the behavior is normal.
1... Does Crusader incorporate a circ pump by-pass in their 5.7L closed cooling system?

2.... Very possible! What happens if you allow the engine to warm up and reach this 200* reading and then run for another minute or so?


I have a 2001 Crusader 5.7L TBI. Motor has a closed cooling system cooled by a raw water pump/heat exchanger. I have been working on the engine using a garden hose, however, it overheats when we tried to take the boat out on a fresh water lake.
So... the garden hose supply is adequate to keep the engine cool, but when the boat is in the water (seawater pump is relying on it's suction only), you see this over-heat scenario..... correct?

Have you ruled out a seawater pump suction breach that the garden hose supply may be circumventing?

I bought it used, history reported to have low hours for what it's worth. The motor overheats only at idle (approx 650 rpm factory set). If I bump it up just a bit to 800+ rpm the motor cools right down to 160-170 on the gauge.
That's an increase of only 150-200 rpm, and to me that's the strange part of this.

To date I have chased the problem by doing the following:

- Rebuilding the raw water pump. New cam, new impeller, new seal. It does not leak and the bearing appear to be fine when tested by feel. Neither the inside of the pump nor the cover are worn.
Which seawater pump? (i.e., Johnson, Sherwood, belt driven, crankshaft pump, etc?)

- Flushing the engine and raw water circuit entirely. I've back-flushed all areas of the motor and cooling system that I am aware of. I am able to put a full-power garden hose into the the elbows w/o any back flow, the same is true for the exhaust manifolds. The heat exchanger tubes are clear. The U-cooler is clear. I pulled the drain plugs on the block and flushed the engine completely with fresh water. By putting water into the hose directly at the u-cooler I get full, clear flow at both elbows.
Question: is this a "half" closed cooling system, or a "full" closed cooling system?
IOW, are the exhaust manifolds seawater cooled, or are they in the closed loop?
(elbows will always be seawater cooled)


- I changed out all of the closed system cooling hoses. The original ones did have a "crunch" to the them and I did flush a lot of grit out of them when I flushed it.

- Installed a new water pump.
As in engine "circulating pump" ???


- Bought a Lisle spill-free coolant "burping" funnel and have removed all of the air from the system as as far as I can tell. Although the engine still appears to need two or three quarts approximately of coolant to meet the 23 qts listed in the manual.
Does your closed cooling system have a coolant recovery reservoir?

- Replaced the heat exchanger cap.
If you have the recovery system, is the new cap correct for a recovery system? (i.e., seals at two areas)

A good working recovery system will prevent coolant loss, and will prevent the need to purge air in the future.

During operation- even when the temp is rising/hot, the exhaust elbows are cool to the touch as are all of the raw water hoses.
This would typically indicate that your seawater pump is supplying an adequate amount of cooling water.


*The one issue I do seem to have is that the exhaust manifolds are hot.
Again.... is this a "half" system or "full" system?

Should they be cool to the touch as the elbows are?
If "half" system, the manifolds may not be as cool as the elbows are.
If "full" system, the manifolds may be very warm to the touch as per what John eluded to.



If so, is it possible they need to be replaced even if I can flush water through them without any seeming obstruction?
I think that your test was good and indicated non-obstructed flow.

Would a faulty temp gauge read like this only at idle? This is the one thing I have not changed out yet.
I would think not!
If it did offer a faulty reading at idle only......., it would be an electrical issue of some sort.

I did check the engine over with a IR temp gun and found no hot spots except for the exhaust manifold, however, I don't think they matched the 200 and rising temp. I always shut it down when it hits 200 degrees. I will double-check this tomorrow and report my findings.

I'm at a loss and would be grateful for any advice.
I'm somewhat puzzled as well.
 
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Good evening CaboJohn and Rick,

Thank you both for your thoughtful replies.

To answer Rick's questions:

- Yes I did see the overheat problem on the lake, where I first tested the boat.
- The raw water pump seems to be a Sherwood from what I can tell.
- The exhaust manifolds are in the closed/coolant loop.
- Yes, I replaced the circulating pump. I used the wrong term.
- Yes, the system has a recovery tank.

CaboJohn,

Thank you for the suggestions and information, which I have followed up on as I'll note below:


Today I mapped the engine with my IR gun, changed the temp sender, and installed a new temp gauge. I found the following:

- When checking temps with the IR gun the morning, I didn't find anything over 173 on the exhaust manifolds. I checked the inlet/outlet and "flag" emblem on the manifolds as reference points. The elbow max temp was 67 and the heat exchanger showed a max of 61. This was while the temp gauge was just about 200.

- When I removed the old sender, I saw that there wasn't any coolant in the passage under it, leading me to think about CaboJohn's suggestion of air in the system. I used a funnel to fill the passage. I installed the new one, and then repositioned the boat/motor so that the heat exchanger was higher and was able to add a bit more coolant. I also filled and installed the recovering tank, which I had removed to clean. Right now it seems that I have reached the manual's amount of coolant (23qts) plus including the tank.

- Yes, to CaboJohn the recovery tank did lower a bit after cooling down so it is still taking coolant in it seems.

Now to the odd findings:

- When I installed the new sender and gauge the temps no longer fall with an increase in idle and slowly runs up to 200 where I shut it off. *****The really puzzling part is that the IR gun at the sender shows a temperature of only 140 degrees give or take. No where near the 200 on the gauge.

- When I checked the exhaust manifolds, along the raw water circuit, the circulating pump and heat exchanger I could only find one really small area on the port exhaust manifold that was showing 190 on the IR gun- a spot just below the elbow. (I did more temp searching over the whole manifold unlike this morning.) However, the inlet and outlet temps on the manifold were not over the 175'ish I'd expect to see given the thermostat's temp nor was the majority of the manifold's "face".

- CaboJohn- I do not have an alarm on the motor yet so I cannot use it as a gauge to tell whether the control module is seeing the same temps or not.

- I did not check the sensor- or what I assume is the sensor on the port side opposite the sender. I did unplug it and it didn't seem to affect the gauge so I plugged it back in.


I'm even more confused now given that the IR gun doesn't reflect the gauge's reading and that with a new sender the temp doesn't fall at all.........................................

Thanks again,

Christian
 
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Christian, your thermostat should have an and air bleed hole in it. If it doesn't drill a small 1/16" hole in it.
With an air bleed hole in it, it should self purge itself of any air in the coolant system!

.
 
Good morning Rick,

Thanks for the suggestion. I frankly don't remember if it does or not. I'll pull it to see. I've not done this before, but have read about in in several threads. It seems the hole should be on the flange and at the 12 O'clock position when installed?

Christian, your thermostat should have an and air bleed hole in it. If it doesn't drill a small 1/16" hole in it.
With an air bleed hole in it, it should self purge itself of any air in the coolant system!

.


Hi Chris,

Thanks for the reply. I will do so, however, I don't know what you're referring to. :) Cancel that per my note below.

ETA: I Googled Chris' suggestion and found the following for anyone following this thread: http://www.autometer.com/tech_faq_answer.aspx?sid=1&qid=57

I would ohm out the manifold and t-stat housing with a good meter. Especially if the IR temp gun shows 140degrees at the sender and the gauge reads higher.
 
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Christian, yes..... the air bleed hole would be in the theostat's flange, but not necessarily indexed in any certain position.

I believe that Chris is talking about the temp gauge sending unit having a good path to negative..... not only via the tapered pipe threads, but also in that the T-stat housing is making negative contact to the intake manifold.

The sending unit acts somewhat like a variable potentiometer for the gauge itself..... so it must have good negative continuity.


.
 
You said there was no coolant when you took out the sending unit, Where is your sending unit located? Did you use tape on the threads when you installed it. If I remember correctly it is recomended that you do not use the tape because it will prevent it from grounding properly.
 
Good morning Rick,

Thanks for the suggestion. I frankly don't remember if it does or not. I'll pull it to see. I've not done this before, but have read about in in several threads. It seems the hole should be on the flange and at the 12 O'clock position when installed?




Hi Chris,

Thanks for the reply. I will do so, however, I don't know what you're referring to. :) Cancel that per my note below.

ETA: I Googled Chris' suggestion and found the following for anyone following this thread: http://www.autometer.com/tech_faq_answer.aspx?sid=1&qid=57


Basically you want to make sure there is no resistance between the temp sender body and the battery Negative. If you wrapped the temp sender in many layers of Teflon tape it would be be slightly isolated and give an incorrect reading. If your temp sender screws into the t-stat housing you will want to make sure the housing has good grounding to the intake and the intake to the cylinder heads.
 
Hi MissNancy- The sender is located on the intake manifold- starboard side at the front- installed vertically. Opposite is the temp sensor. I did not use teflon tape, however, I did use a Permatex liquid sealant. I plan to pull it out today to see if there is coolant under it as well as clean up the threads.

You said there was no coolant when you took out the sending unit, Where is your sending unit located? Did you use tape on the threads when you installed it. If I remember correctly it is recomended that you do not use the tape because it will prevent it from grounding properly.

Thanks Chris. As noted above my sender is in the intake manifold. I will check it today as well. I also plan to run a line straight from the sender to the gauge and another from the gauge directly to ground to see if that does anything after cleaning up the threads.

Basically you want to make sure there is no resistance between the temp sender body and the battery Negative. If you wrapped the temp sender in many layers of Teflon tape it would be be slightly isolated and give an incorrect reading. If your temp sender screws into the t-stat housing you will want to make sure the housing has good grounding to the intake and the intake to the cylinder heads.

If the sender/gauge don't show any changes with new wiring and ohm check, I guess I'll pull the elbows and manifolds just to check them even though they seem to have clear flow. I don't know where else to turn at this point.

Thanks for the replies and suggestions.
 
I have fooled with overheat issues more than I care to admit, and assuming I was looking at the correct sender for the gauge I have never seen an IR shot on the cast iron next to the sender vary more than 5 degrees from the gauge. So I would really chase that down before I would conclude that I even really had an overheat problem. Given a choice between 200 on the gauge and 140 on the IR gun, I would believe the gun every time, if you are really shooting the correct spot. Also given the rpm sensitivity, you might want to check system voltages at idle and at 800 rpm where the problem seems to go away.

And the lack of coolant under the sender is just plain wrong. You have an air bubble. That's a fact and it may be part, or even all of your problem. Putting a hole in the thermostat always helps getting out the air (that is a good suggestion), but three or more heat and cool cycles are needed to be sure. So you can't be sure have or have not found it if you a looking for a one day fix. You can get a head start if you fire it up and rev it to move the air bubble for a minute (or less) then shutdown, pull the cap and add fluid as needed. Do that several times prior to heat up.

Right now best guesses would be: Either you are shutting it down early due to a faulty temperature reading when there really is not a problem, or you have a giant air bubble that does not get moved well because of the low flow though the block when the bypass is in effect (heat exchanger not seeing coolant flow). The air bubble lodges in the top of intake manifold, gets heated quickly to 200 degrees from #1 or #2 (depending on which side it is) and you are getting a correct temp reading of the air. However the air does not transfer enough heat to cast iron around the sensor to get it that hot, and the coolant is still only at a much lower temp. You rev the engine, everything moves and suddenly the sender sees coolant and drops to 160-170 that is the actual coolant temp.

Or some combination of the above. The point is there is a lot of evidence that something of this sort may be happening and you have two areas (temp gauge and air bubble) on which to focus. There is no reason to suspect elbows and manifolds. Pulling them is a pain, and expensive when you consider new gaskets, which are essential as that is one place where you really do not want a leak.

Good luck,
CaboJohn
 
OK for this afternoon's findings:

-I checked the sender when the gauge read just before 200 at which point I shut the motor down. By the time I got the wire unhooked and check the resistance I got 102 ohms. By extrapolation only from autometer's link above it seems the gauge is accurate and the sender is OK.

-For the heck of it, I ran a new wire from the sender directly to the gauge, bypassing the harness, and a ground from the gauge directly to the battery ground. It didn't make a difference.

-I loosened up the sender and found coolant trying to seep out, so apparently I was able to get the air out of that point at least, although I am still "bow down" a little in orientation. The threads were also clean by appearance so I don't think I jeopardized the ground using the Permatex liquid sealant.

- When I again checked the sender housing/intake manifold I got 140 degrees on the IR gun when the gauge read 200. All other hoses were cold, indeed sweating substantially, in the raw water loop on hose power. I checked the manifolds at 200 on the gauge and they read 160's on the gun.

- The only things I noticed, and who knows if it's relevant, is that the starboard exhaust showed more "smoke" than the port side does. When I open the flapper I can see the exhaust whereas on the port side a see only faint wisps. Neither side smells like coolant. Wondering about a head gasket...........

- Next on to pulling the thermostat and drilling a hole in it...............


Anyone have a tech-support number for Pleasurecraft/Crusader? I think I have a back-door number somewhere through my email when I inquired about the model and year of the engine.

Thanks.

Christian
 
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Hi CaboJohn,

Thanks for the reply. I missed this before posting the above. Your thoughts make me feel better for sure regarding the elbows and manifolds. I will continue to pursue the air bubble. My next step is to drill the thermostat in a few minutes and see how that works out.

What I have found that is different and posted earlier is that the engine temp is no longer coming down with an increase in idle speed. That suddenly changed for some reason. When checking the sender today there was coolant under it as it tried to seep out before I had it completely out. I will double check my sender part number to be sure it is the right one. I didn't realize there were different ones. The one I bought came from my local NAPA. It was clearly marked on the package as a Crusader part.

I have been taking an IR temp reading right in front of the sender and at its base.

Thanks again for your continued help.

Christian

I have fooled with overheat issues more than I care to admit, and assuming I was looking at the correct sender for the gauge I have never seen an IR shot on the cast iron next to the sender vary more than 5 degrees from the gauge. So I would really chase that down before I would conclude that I even really had an overheat problem. Given a choice between 200 on the gauge and 140 on the IR gun, I would believe the gun every time, if you are really shooting the correct spot. Also given the rpm sensitivity, you might want to check system voltages at idle and at 800 rpm where the problem seems to go away.

And the lack of coolant under the sender is just plain wrong. You have an air bubble. That's a fact and it may be part, or even all of your problem. Putting a hole in the thermostat always helps getting out the air (that is a good suggestion), but three or more heat and cool cycles are needed to be sure. So you can't be sure have or have not found it if you a looking for a one day fix. You can get a head start if you fire it up and rev it to move the air bubble for a minute (or less) then shutdown, pull the cap and add fluid as needed. Do that several times prior to heat up.

Right now best guesses would be: Either you are shutting it down early due to a faulty temperature reading when there really is not a problem, or you have a giant air bubble that does not get moved well because of the low flow though the block when the bypass is in effect (heat exchanger not seeing coolant flow). The air bubble lodges in the top of intake manifold, gets heated quickly to 200 degrees from #1 or #2 (depending on which side it is) and you are getting a correct temp reading of the air. However the air does not transfer enough heat to cast iron around the sensor to get it that hot, and the coolant is still only at a much lower temp. You rev the engine, everything moves and suddenly the sender sees coolant and drops to 160-170 that is the actual coolant temp.

Or some combination of the above. The point is there is a lot of evidence that something of this sort may be happening and you have two areas (temp gauge and air bubble) on which to focus. There is no reason to suspect elbows and manifolds. Pulling them is a pain, and expensive when you consider new gaskets, which are essential as that is one place where you really do not want a leak.

Good luck,
CaboJohn
 
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CaboJohn- Your last post put me a search............How about this finding! I found my sender packaging from NAPA (after three searches through the gnarly trash :)) and just spent 15 mins online tracking it around. It seems that this sender is for a DUAL station. I also found a review online somewhere when searching in which a customer said that it read about 40 degrees too high IIRC for his application. Could he have had a single gauge too? Because mine is a used motor there very well could have been a dual-station sender in it when I got it, so swapping it wouldn't have changed anything obviously.

I'm just not sure if a dual-station sender would read higher or lower in a single gauge use..............

You may have hit it on the head?!

I just found this on Jamestown Dist' site regarding Teleflex troubleshooting temp gauges:

"Dual Station installations:
  • When replacing one gauge in a two station installation, the second gauge may need to be replaced as well.
  • Mixing two gauges from different manufacturers to one sender may cause an error in both gauges.
  • If one gauge fails the second gauge will read much higher than expected."


In my case then, the dual station sender thinks one gauge has failed and is reading too high?
 
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No such luck. I wired up the old temp gauge I had with the current one and it's still reading 200 before I shut it off and 145 at the sender housing on the IR gun. Once it cools down I'll drill the thermostat. I was hopeful the sending unit was the problem.
 
If the temp did not appear to drop when you hooked up a second gauge, then you hooked it up wrong. The reading will drop when you do that test whether you have a single station or duel station sender. But if you are running a single gauge (per engine) then you must have a single station sender (not a duel station as you now believe you have) or the gauge will read the wrong temp (too high, as you may have discovered).

CaboJohn
 
Hi Rick,

No it's a single station center console.

If this is a Dual Station boat...... are you using Dual Station sending units?



.

Hi CaboJohn,

The temp did drop so it was hooked up correctly. ( I had my wife watch the gauge as I unhooked the second one at which point it clearly jumped up.) The problem was they were still reading 200 degrees before I shut down the engine, but still 145 at the intake manifold in front of the sender per the IR gun. I didn't get a chance to drill a hole in the thermostat as it started to rain, but will do so tomorrow. I ordered the proper single station sender, which hopefully will arrive this week.

After I drill the hole and reinstall, I will try to purge any air as you noted. Right now I've got at least a dozen or so start/cool down phases and 24 quarts of coolant in the system including the overflow/recovery tank. Hopefully, I can dislodged any air that may be trapped once I have done so.

If the temp did not appear to drop when you hooked up a second gauge, then you hooked it up wrong. The reading will drop when you do that test whether you have a single station or duel station sender. But if you are running a single gauge (per engine) then you must have a single station sender (not a duel station as you now believe you have) or the gauge will read the wrong temp (too high, as you may have discovered).

CaboJohn
 
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Good morning Rick,

Upon pulling the thermostat there is a factory bleed hole in it so I can rule out the lack of a hole anyway. I will try several start/stops now that I have to put more coolant in and see if I can dislodge any air.
 
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Upon pulling the thermostat there is a factory bleed hole in it so I can rule out the lack of a hole anyway.
That's good!

Christian, in terms of elevation, where is the coolant level in the heat exchanger compared to the coolant level in the thermostat housing?
In other words.... at what elevation is the heat exchanger mounted on this engine.... and where does that put the coolant level?

As long as you continue to top off the coolant level within the heat exchanger, the circ pump will charge the block with coolant, and the system should self-purge!



.
 
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Hi Rick,

My thermostat is located "in" the heat exchanger. There is an inlet into the heat exchanger that has the manifold and bypass hoses attached to it for feeding the exchanger when the thermostat opens. So it's at the same level but at the top of the heat exchanger in terms of elevation. I have been trying to purge the air by putting the boat on the trailer in a bow-down position and using the Lisle funnel with an extension to be sure it's higher than the hoses from the exhaust manifolds and higher than the intake manifold where the sender is located. I think I have done so.

However, the one glaring problem I seem to have is that temperature disparity between the manifold beside the sender and the gauge. I installed the alarm today, and ran the motor just over 200 degrees and it did not sound. Each time I have used the IR gun to check temp at the sender location is hasn't exceeded 145 degrees. I tried ground the sender directly to the battery today as well as grounding the gauge directly, which didn't make a difference.

I have ordered a new sender. Frankly, if that doesn't work I am at a total loss. My temps keep climbing now regardless of RPM's but I cannot find a hot spot anywhere on the motor when mapping the raw water and closed cooling loops with the IR gun.

Thanks for the reply.

Christian

That's good!

Christian, in terms of elevation, where is the coolant level in the heat exchanger compared to the coolant level in the thermostat housing?
In other words.... at what elevation is the heat exchanger mounted on this engine.... and where does that put the coolant level?

As long as you continue to top off the coolant level within the heat exchanger, the circ pump will charge the block with coolant, and the system should self-purge!



.
 
With a car/truck engine and a radiator, or a boat engine with a close or raw water cooling system....... here's what happens... or should happen:

The engine circulating pump "intake" is at a low point, and will generally always be submerged in coolant (i.e., raw water or ethylene glycol mixture).

The thermostat is holding back the coolant, and is what causes the circulating pump to mildly pressurize the block/cylinder heads.

The portion of the system "down-stream" of the thermostat will be under mild negative pressure.
(the
pressure "differential" is what makes for a good supply and return for a water heater or cabin heater installation)

Point being (I hope):
As long as the radiator/heat exchanger coolant level is up to snuff, and the thermostat is installed and is working correctly ...... the circulating pump will generally supply enough mild pressure (upstream if the thermostat) to purge any air ...... and should also purge air from the coolant's path from the thermostat area back to the Heat Exchanger.

I can't quite explain why you are having trouble burping the system of air.

Are you able to post photos of your cooling system for us?


.
 
Good morning Rick,

Thanks for the reply. Sure. I don't know if it is air or not, as my cooling paths seem to alright on temps with the IR gun. The hottest area are the manifolds in the 170's.

 
It's difficult to tell from the photo.... but the Heat Exchanger appears to be only a tad bit lower than the front of the intake manifold. Yes/no?

Coolant enters the Circ pump, from there it enters the cylinder block.
Looks as though it then leaves the intake manifold, and makes it's way to the lower port of each manifold.
From there, it looks as though it is directed to the Heat Exchanger.


IMG_20140902_084015_394_zps0e245d23.jpg
 
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I'd put more stock in the Accuracy of the IR gun vs the gauge as the gauges are notorious for their inaccuracy.

a dual station sender used in a single station application will produce a "hotter than normal" result assuming the sender and gauge use the american standard. many other options exist so without specific part numbers, its a guess at best. you can read the impedance (resistance) of the sensor with a good quality digital meter and see if it compares favorable with the IR gun. you can also substitute known resistor values to validate the gauge reading.

have you verified the raw water flow, from the pump, is adequate?
 
Hi Rick,

Thank you for hanging in there with me. The heat exchanger is just a little bit higher than the intake manifold when the boat is sitting at the waterline attitude I'm pretty sure. That's why I have put the bow down to try and get any air to rise to the heat exchanger/Lisle funnel when I've tried to purge it. Your assessment of the water path is correct: To the heat exchanger, through it and then pulled back to the water pump. There is also a bypass at the heat exchanger where the coolant converges from both intake manifolds.

It's difficult to tell from the photo.... but the Heat Exchanger appears to be only a tad bit lower than the front of the intake manifold. Yes/no?

Coolant enters the Circ pump, from there it enters the cylinder block.
Looks as though it then leaves the intake manifold, and makes it's way to the lower port of each manifold.
From there, it looks as though it is directed to the Heat Exchanger.

Hi MakoMark,

Thank you for your reply. I have wired two gauges to the dual sending unit temporarily until the single station arrives. I did pull the sender wire from one and watched the gauge jump 30 plus degrees as you noted.

I haven't done anything "scientific" to verify the raw water flow. I did pull the hose off of the U-cooler so observe the flow and then I used the IR gun to see that the temp is 62 on both elbows and slightly higher at the exhaust existing the transom, with a temp as it enters the U-cooler from the raw water pump of approx' 59 degrees. Those numbers at idle speed on the hose.

I'd put more stock in the Accuracy of the IR gun vs the gauge as the gauges are notorious for their inaccuracy.

a dual station sender used in a single station application will produce a "hotter than normal" result assuming the sender and gauge use the american standard. many other options exist so without specific part numbers, its a guess at best. you can read the impedance (resistance) of the sensor with a good quality digital meter and see if it compares favorable with the IR gun. you can also substitute known resistor values to validate the gauge reading.

have you verified the raw water flow, from the pump, is adequate?

I had a long talk with Mike at PleasureCraft/Crusader's tech support today. Very nice guy, who was willing to talk about things with me. Essentially, he pointed to the sending unit given my temp differential with the IR gun and echoed the strong suspicion of an air pocket as both CaboJohn and Rick have been suggesting. He said especially in the older motors it can be really tough to chase it out. So much so that he had had mechanics call and "yell at him" claiming they had adequately burped the system only to have them call back later once the air had been dislodged. According to him new models actually have a plug on the heat exchanger that was designed into the system to purge air. In a nod to CaboJohn's earlier post he echoed almost exactly what he said, that an air pocket may causing steam to build under the sending unit, artificially inflating the temp on the gauge. Of course that assumes the gauge is accurate and the new sender once installed still shows the engine running hot. Thanks again to CaboJohn's insight. We also discussed both the exhaust manifolds and elbows, however, given the temps I was getting he felt they were probably OK, but that it wouldn't hurt to verify by pulling the elbows if I am still not able to burp the system after trying several more times with the new sender installed.

Right now my plan is to wait until the new sending unit arrives, install it and then see if I suddenly get a reading that closely echoes the IR gun. If that still reads high I'll continue to try and burp the system. If I am still having problems I'm considering installing a double-ended hose barb at the high point in one of the manifold outlet hoses, which I'll tap for a bleed screw. The hose I used to replace the factory one is wire reinforced hose that I bought locally and sized to fit so they ride a little higher than the formed factory hoses. I'm wondering if this makes it tough to purge the air?

Thanks again for everyone's continued help and suggestions.

Christian
 
Note: You need a single helm station sensor for a single station helm, and a DUAL helm station sensor for a dual helm station.

Guess how I found THAT out!

Jeff
 
Christian, we're all glad to hang in there with you!

Hi Rick, Your assessment of the water path is correct: To the heat exchanger, through it and then pulled back to the water pump. There is also a bypass at the heat exchanger where the coolant converges from both intake manifolds.
What is meant by "both intake manifolds"?


Hi MakoMark,
We also discussed both the exhaust manifolds and elbows, however, given the temps I was getting he felt they were probably OK, but that it wouldn't hurt to verify by pulling the elbows if I am still not able to burp the system after trying several more times with the new sender installed.
With what we call a "Full closed cooling system" (exhaust manifolds in the closed loop), the exhaust elbows will be blocked off from the exhaust manifold coolant.
Other than offering proper "spent" seawater flow, the elbows will not affect the exhaust manifold cooling.

Jeff is correct re; the dual station boat engine temperature sending units.
These must be correct for a dual station boat that has a temperature guage at each helm station.


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Good morning Rick and Jeff.

My mistake Rick. A long night last night, so I clearly wasn't paying close attention to what I had written. I meant to say both "exhaust manifolds" not intake manifolds. Yes, I do realize that they are separated. Mike was considering a restriction in the elbows and the exhaust manifolds separately. I lumped them together when typing.

Yes, like Jeff I realized this through trial and error too. I now have two gauges wired to the sending unit. I will go back to a single gauge when I install the new sender.

Thank you both.

Christian, we're all glad to hang in there with you!



Jeff is correct re; the dual station boat engine temperature sending units.
These must be correct for a dual station boat that has a temperature guage at each helm station.


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