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Duskey
New member
Username: duskey
Post Number: 1
Registered: 01-2010
| | Posted on Thursday, January 28, 2010 - 08:11 am: | 
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I have Twin 1999 Mercruiser 7.4L inboards one engine will start to overheat above 2500 rpm.
I've installed new exhaust manifolds and elbows (no shutters) new thermostat, new raw water pump, just removed the heat exchanger end caps and the exchanger looks very clean. It doesn't overheat at idle...I have no idea what to do next! Any suggestions? |
chiefalen
Advanced Member
Username: chiefalen
Post Number: 549
Registered: 03-2008
| | Posted on Thursday, January 28, 2010 - 08:23 am: |
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Pull the long hose off the t-stat housing that comes out the transom and hold it up in the air, with water going to the drive or boat in the water start the boat and see if you have good water going to the t-stat housing.
The water should shoot 12" or more into the air. |
Kghost
Senior Member
Username: kghost
Post Number: 1218
Registered: 07-2008
| | Posted on Thursday, January 28, 2010 - 08:37 am: |
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A common problem with the Bravo water intake systems is,
At the transom where the hose goes into the transom from the motor side it is held in the hole by a PINCH method.
The surrounding material becomes swelled up due to oxidation and squeezes the hose down and restricts water flow to the pump.
Here are some pics of my suggested source of the issue.
 |
Duskey
New member
Username: duskey
Post Number: 2
Registered: 01-2010
| | Posted on Thursday, January 28, 2010 - 09:30 am: |
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The engines are straight inboards not sterndrive models, sorry for the confusion, I don't see another topic area for strictly inboards.
I have Velvet drive 5000 series transmissions. The outflow of water at idle seems the same at both exhaust ports (port and starboard) It really blows alot of steam above the 1500 RPM or so. Can I still pull the thermostat hose and verify good water flow? |
Kghost
Senior Member
Username: kghost
Post Number: 1219
Registered: 07-2008
| | Posted on Thursday, January 28, 2010 - 09:41 am: |
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Take a picture of your motor showing water hose placements and post it.
Also are you sure you have the incomming water hose going to the correct water pump inlet connection and not the outlet???? If they are incorrectly positioned then that would definatley reduce the water flow!! |
makomark
Senior Member
Username: makomark
Post Number: 2092
Registered: 09-2008
| | Posted on Thursday, January 28, 2010 - 10:50 am: |
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Dusky:
Assuming that you correctly bled the air out of the closed side and have adequate raw water flow, I'd suspect the oil cooler(s). The usual location is on either side of the oil pan.
Probably easier to measure the raw water flow from the pump first. If ok, proceed to the oil cooler inspection.
Follow the hose from the raw water pump and you will find them. I'd expect the first one you come to is most likely to be the culprit. |
chiefalen
Advanced Member
Username: chiefalen
Post Number: 551
Registered: 03-2008
| | Posted on Thursday, January 28, 2010 - 11:00 am: |
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Maybe you have mussles or some other obstruction, blocking the intake, that is why i asked you to see if you have good water going to the t-stat, where it branch's off.
See good water to the t-stat then the obstruction is further down the " pipe line "
And i understand the steam problem, and it scares you.
First good water to t-stat.
Then if good water to t-stat do a vacuum test.
here is the links.
http://www.secondchancegarage.com/public/186.cfm
http://www.users.bigpond.com/ergoff/vac1.htm
Keep us posted after checking the water flow and doing the vacuum test we can go from there.
I don't want to scare you anymore with what it could be. Just conjecture at this point.
Good luck ! |
Duskey
New member
Username: duskey
Post Number: 3
Registered: 01-2010
| | Posted on Thursday, January 28, 2010 - 12:11 pm: |
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I believe the water connections are correct as I did not change any hoses only off and on. Here's some pictures I found I already had, kind of hard to see the hose connections. I seem to have good flow out the exhaust, maybe the circulating pump?
I will have to put the exchanger back on after the new end gaskets arrive, in the mean time I will check the flow through the oil cooler. I didn't bleed any air out of the system, just filled with anti-freeze. It runs right at 160 degrees at idle after warmed up, only at speed does it begin to overheat. I'll look into doing the vacuum test.  |
Kghost
Senior Member
Username: kghost
Post Number: 1223
Registered: 07-2008
| | Posted on Thursday, January 28, 2010 - 12:54 pm: |
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Is it me or is there something missing??
Where is the raw water that should be going thru the elbows??? What is cooling the exhaust?
I do not have a big block manual here so i can look at the water flow diagram........ |
Kghost
Senior Member
Username: kghost
Post Number: 1224
Registered: 07-2008
| | Posted on Thursday, January 28, 2010 - 01:05 pm: |
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I am looking at manual 16 and there is a "second type of closed cooling system that must be yours.
here is a diagram of it.
Looks like raw water comes in thru FUEL FILTER COOLER and then into pump, from pump it goes to exchanger, from echanger it flows to the bottom of the exhaust manifolds and out the elbows, similar to a raw water only system.
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Duskey
Member
Username: duskey
Post Number: 4
Registered: 01-2010
| | Posted on Thursday, January 28, 2010 - 01:32 pm: |
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That appears to be the cooling system I have.
I just don't understand how it over heats when I seem to have very good flow, at least I see good volume at idle. anyway I'll keep digging! Thanks for everyone's help, I'll keep you all informed if/when I find the problem. |
Kghost
Senior Member
Username: kghost
Post Number: 1225
Registered: 07-2008
| | Posted on Thursday, January 28, 2010 - 01:37 pm: |
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Well when idle is good and high speed is bad then you either have a incoming flow issue or a outgoung flow issue.
Follow the clear arrows in the diagram and that shows the RAW water path.
You have a fuel cooler in line before the pump, you also have a transmission cooler after the pump.
Either of those could have something STUCK inside...............It does not take a lot of raw water to cool an engine at idle.
Above idle is a different story..........any restriction will cause a reduction in flow. |
James Norvell
Member
Username: sonshinefishing
Post Number: 83
Registered: 12-2008
| | Posted on Thursday, January 28, 2010 - 11:46 pm: |
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If the boat is kept in the water you could have marine growth in the raw water intake. Sounds like some kind of raw water inlet flow restriction. |
cobe marine
Member
Username: cobe_marine
Post Number: 20
Registered: 01-2010
| | Posted on Friday, January 29, 2010 - 02:40 pm: |
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how long have you had this problem? ever since you've owned the boat or did it start recently? |
Duskey
Member
Username: duskey
Post Number: 5
Registered: 01-2010
| | Posted on Sunday, January 31, 2010 - 09:21 am: |
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I've had this problem since late last summer, (the boat is always in the water, it is 8 tons)the first thing we replaced was the raw water pump, and cleaned all the debris out of the system. Then the exhaust manifolds and elbows.
Yesterday I removed the first cooler in line with the raw water pump, the transmission cooler, and I found a 1/2" sized, what looks like part of the raw water impeller. Other wise the cooler holes looked fairly clear, I then moved to the Mercruiser "Cool Fuel" cooler and there is definitely not a blockage there it is just a straight through pipe, I next pulled the oil cooler tube and found a bit more, what looked like sea weed in it, not much, but looked to be enough to imped flow a little. That's as far as I got at this point. After seeing the impeller piece in the trans cooler I will again pull the raw water pump later this week and inspect it again. I'm waiting on seals for the heat exchanger, in the mean time I'll clean the cooler tubes, trans, oil, and exhanger. I'm going to also pull the raw water pump and verify it is still in good shape.
The above cooling system drawing shows the fuel cooler before the pump, it is actually between the transmission cooler and the oil cooler, very tough to get at on the lower port side under the motor mount and exhaust manifold and very near the port fuel tank.
I don't really see these minor blockages as the problem, but I'll find out as soon as I clean them all and put it back together again. Any suggestions on how to clean these cooling tubes?
I have some small engine cleaning brushes but they are a bit too tight to push through the small holes.
Thanks for your suggestions, work will continue, as it's another overcast weekend here in Tampabay area, no boating in this weather. |
Kghost
Senior Member
Username: kghost
Post Number: 1233
Registered: 07-2008
| | Posted on Sunday, January 31, 2010 - 09:38 am: |
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"""""I don't really see these minor blockages as the problem""""
You would be surprised what a little blockage here and a little blockage there adds up to in total blockage.
Just remember that your system is not overheating? correct? Just steam correct?
Well restricted flow at higher rpms will definately cause this. Especially a piece of the impeller.
Be dillagent and look real good at all points of cloggage, ie: where ever a transition of hose to hardware, that could be where another piece of impeller could be hiding........
good luck! |
Guy Gaspar
Senior Member
Username: guyjg
Post Number: 5553
Registered: 08-2006
| | Posted on Sunday, January 31, 2010 - 12:05 pm: |
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Use a rifle barrell bore brush and rod for the small holes. |
Duskey
Member
Username: duskey
Post Number: 6
Registered: 01-2010
| | Posted on Monday, February 01, 2010 - 11:49 am: |
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Here's pictures of the debris I noticed in the transmission cooler, and next the oil cooler, and upon standing the trans cooler on end and tapping on the bench more came out (final picture). I'm now believing that after seeing all this, it may be the problem. I'll clean all these coolers out, as well as the exchanger, also inspect the raw water impeller and put it back together. Thanks....I'll update all later.
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makomark
Senior Member
Username: makomark
Post Number: 2111
Registered: 09-2008
| | Posted on Monday, February 01, 2010 - 08:42 pm: |
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Don't be surprised if you get more stuff out of the holes. You may want to pressure test the coolers while you have them out, they have been at work for over a decade. Not certain what their expected service life is but would venture a guess saying not much more is left. I think they are fairly reasonable, commpared to most things with a 'marine' label. |
Kghost
Senior Member
Username: kghost
Post Number: 1251
Registered: 07-2008
| | Posted on Tuesday, February 02, 2010 - 06:30 am: |
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Good find!!
I would agree, that much of a old impeller will definatley cause water flow problems...........
May want to take to a radiator shop and see if they can clean them for you.
Again good find!! |
Duskey
Member
Username: duskey
Post Number: 7
Registered: 01-2010
| | Posted on Saturday, February 06, 2010 - 05:13 pm: |
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Update on overheating problem....I got everything back together today, heat exchanger, trans and oil cooler, checked the raw water pump impeller etc......The engine still produces tons of steam at anything above 1500 RPM and begins to overheat. I did notice that the port exhaust elbow was much hotter than the starboard one. I pulled the inlet water hose from the starboard manifold to verify water flow, and it seemed to have a very strong flow. I then pulled the port hose, reconnecting the starboard and verifed approximately the same amount of flow....
I don't believe there is a problem with this, in fact I wanted to do something, so I swapped raw water pumps from my starboard engine to the port engine with the same result.
Could I have a cracked head? An exhaust leak into the exhaust water? Remember, the exhaust and elbow are brand new, this is what I was told was originally wrong. I'm totally lost.
Will taking a compression check on the port head tell me anything?
I'm very sure that I have ample flow through the water cooling system.
I believe there is something wrong inside the engine.
I just don't know what to do next. Any suggestions?
Thanks all. |
makomark
Senior Member
Username: makomark
Post Number: 2148
Registered: 09-2008
| | Posted on Sunday, February 07, 2010 - 09:17 am: |
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Get a cooling system pressure tester and run the series of tests it can perform. It will find what you suspect, if that is the cause. |
Kghost
Senior Member
Username: kghost
Post Number: 1271
Registered: 07-2008
| | Posted on Sunday, February 07, 2010 - 09:26 am: |
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Makomark,
I dont think this will help any, He has a closed cooling system and the issue is the fresh water side of the system.
The engine is or should be maintaining ~ 160-180 degrees when fully warmed up.
Duskey,
If you follow the FRESH water flow of the diagram I posted the next place for fresh water to be inhibitad is the HEAT EXCHANGER.
Have you removed that yet and looked at it in detail to see if the fresh water passages are free and clear.
The fresh water passes thru it and then goes thru the exhaust manifolds then up thru the elbows....
Some how fresh water is being restricted from exiting the manifols/elbows.....
That is my only suggestion at this point... |
chiefalen
Advanced Member
Username: chiefalen
Post Number: 598
Registered: 03-2008
| | Posted on Sunday, February 07, 2010 - 10:39 am: |
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Hold up. Did you ever do a vacuum test. Cheap and easy. Here is 2 links.
http://www.secondchancegarage.com/public/186.cfm
http://www.users.bigpond.com/ergoff/vac1.htm
The vacumm test will reveal how the internals are working, me i would stop everything and perform it . |
Kghost
Senior Member
Username: kghost
Post Number: 1272
Registered: 07-2008
| | Posted on Sunday, February 07, 2010 - 10:48 am: |
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I dont think that is necessary,
If he had a head gasket leak the antifreeze would be burning off and he have a loss of it and would be overheating as a result of NO antifeeze.
Remember this is a CLOSED cooling system.
The steam is a result of HOT fresh water vapor.
Look closely at the diagram in a earlier post. |
chiefalen
Advanced Member
Username: chiefalen
Post Number: 600
Registered: 03-2008
| | Posted on Sunday, February 07, 2010 - 10:51 am: |
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Ghost how do we know for sure. Takes all of 15 minutes to perform. Costs nothing, and we are running around chasing our tails here.
You want to help, same as me.
Do the test. He says it's now only the port side, that side always runs hotter anyway. |
Kghost
Senior Member
Username: kghost
Post Number: 1273
Registered: 07-2008
| | Posted on Sunday, February 07, 2010 - 11:23 am: |
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""Ghost how do we know for sure.""
We will know if he responds and says he is NOT loosing any antifreeze.
I still think he has a obstruction in his incomming water lines. Fuel cooler, oil coolers, or heat exchanger....
I feel it is a blockage of Fresh water either comming in or going out. |
Duskey
Member
Username: duskey
Post Number: 8
Registered: 01-2010
| | Posted on Sunday, February 07, 2010 - 02:56 pm: |
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Thanks for the responses after yesterday’s trials, I decided the flows into the manifolds from the heat exchanger were not the same, so I went to the store and spent $30 on 1" tubing to swap the exhaust inlet sides, I did notice one elbow was cool the other hot. I wanted to see if I could swap the outputs of the heat exchanger and make the other side cool. This would tell me if the flows were enough and that internally the engine was OK. So I crossed the hoses and sealed them so the left hose out of the heat exchanger was now cooling the right exhaust, which was the "hot" one, and the right output to the left exhaust.......and now the left one got hot. This tells me the exhaust manifold that gets the first outlet from the heat exchanger stays cool. So I pulled the exchanger off to see that it is positively clean. I now believe, as some of you suggested before, that I have a flow problem in the pick-up or sea strainer. I know the sea strainer basket looks clean, but I need to dig deeper. I have someone routinely clean the hull, but I need to ask him to pay special attention to the pickup area of the port engine.
I'm glad I did the heat exchanger outlet swap as this tells me there is nothing wrong inside the engine. (I would have lost anti-freeze if I would of had a blown head gasket, but the fresh water side always seemed to circulate and never loose coolant or get over pressurized, so I didn't spend time messing with the fresh water (anti-freeze) side).
I need to examine the pick-up and sea strainer with more attention....I'm fairly sure after today’s test it's in front of the pump now. (remember I swapped the pumps yesterday, and the starboard engine still remains cool without the steam). I feel the $30 for hose was worth it as now I’m confident there are no internal engine issues.
ghost and chief have suggested all along that I have an inlet/pickup obstruction. After all I’ve done I believe this to be the case. The water is stinking cold now so I’m not getting in with my dive gear to look at this, but I can have the bottom cleaner take a closer look. I’ll examine the sea strainer better. Any other suggestions? Is there anything I can get at and check for inside the hull? I’m feeling better that I'm getting close to the root of this issue.
Thanks |
Kghost
Senior Member
Username: kghost
Post Number: 1275
Registered: 07-2008
| | Posted on Sunday, February 07, 2010 - 03:13 pm: |
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Based on the flow diagram what you are saying is the exact opposite of what should be seen.
The fresh cold water enters the heat exchanger on the right bottom side and exits the top right side to right manifold and the excess water flows thru the heat exchanger to the left and out to the left side manifold.
With and if this is the way your hoses are routed than the one on the left should be the warmest as the water would be warmer after flowing thru the heat exchanger.
So if the right one is getting hot and the left one is cool (original hose configuration) then there may be some restriction still affecting the right side.
After your hose swap and transfering the hot to the left tells me that the output from the heat exchanger still may have a flow issue.
I also agree it just may be a overall incomming water flow problem and the right may infact get the lesser amount of water.
I stiil at this point feel along with a slight incomming water restriction, there still may be something causing flow restriction in the heat exchanger. |
Duskey
Member
Username: duskey
Post Number: 9
Registered: 01-2010
| | Posted on Sunday, February 07, 2010 - 03:57 pm: |
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Inside the heat exchanger the water does come in at the right side and flows through the cooling tubes directly to the left side exhaust manifold first, then back and forth twice until at the end it flows out to the right side exhaust manifold last. Ample flow goes directly to the left heat exchanger outlet. So which ever manifold is connected to the left output will remain cool. After flowing through the rest of the heat exchanger the final output of salt water (the boat is actually in an intracoastal marina, Bay Pines (St. Pete) to be exact) is surely the hottest and is the right manifold. My wife and I both have assessed the situation and we surely agree now that we just don't seem to have enough flow to remain cool by the time the raw water reaches the end of the line, the right exhaust manifold.
I guess I could actually swap heat exchangers from the cool running engine (starboard) to this engine, but we think it is pointless as we both feel there is just not enough flow as the majority flows directly to the first heat exchanger outlet. The design of the heat exchanger is just too simple we can see clearly that there are no obstructions in the tubing and end chambers.
Picture 1 shows the exchanger at the far left the curved inlet is the raw (saltwater) water input which when installed on the engine comes directly out of the oil cooler and is on the right side of the engine as it is now upside down in the picture. The straight down “outlet” beside the curved one is actually the right side exhaust manifold outlet. The deceiving part is that the raw water inlet (curved one) doesn’t flow right out the outlet beside it. The water flows directly across the bottom through the bottom tubes to the left side (straight down pipe on the right side of the first picture). This is the highest flow at first, so whichever side of the exhausts I have connected to this outlet remains cool.
I took a couple pictures of the ends of the heat exchanger and you cannot see in the picture, but I can see directly through all these tubes and see they are not blocked, but I also pushed a small brush through each hole to remove any small build-up of slime. But after doing half of them decided it was not really removing anything, and decided not to risk damaging any of the tubes.
The pictures of the ends of the exchanger with the end caps removed show all to be quite clear(in our opinion). With this second time looking at the exchanger we feel confident we should look elsewhere….to the pick-up and sea strainer. I certainly do appreciate your responses as it makes me re-evaluate each next step….thanks again.
I not sure how to examine the pick-up or sea strainer closer, but will next investigate this process.
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Kghost
Senior Member
Username: kghost
Post Number: 1276
Registered: 07-2008
| | Posted on Sunday, February 07, 2010 - 04:41 pm: |
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Ok I now understand the water flow thru the heat exchanger, Thanks. Makes sense as it would go the the least restrictive outlet and thus the left would most likely get warmer in that case.......
I am not sure where you water intake is and if you can get to it from the bildge area or not.
Carefully inspect the hoses for colapsing or possible clogging, Salt water will do wonders on rubber hose!!!
Inspect the strainer carefully and look for anything that may look out of place such as swollen hoses etc.
I would imagine that the water pick up is not directly under the strainer?
If it is the possibly remove the strainer and hav a look see if you can?
Not there and cant see what your situation is......
I use to live in Northeast ST Pete. about 5 mins from the Gandy Bridge!! Back in the late eighties....I dont remember where bay pines is as it has been a long time!!
Keep at it and let us know what you find! |
Duskey
Member
Username: duskey
Post Number: 10
Registered: 01-2010
| | Posted on Sunday, February 07, 2010 - 04:53 pm: |
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The raw water pick-ups/strainers are just behind the transmissions towards the center of the hull, and yes the strainer is mounted six inches from the valve which goes straight through the hull. The hose from the strainer to the pump is that fiber type hose which seems much tougher than the rubber hoses on the engine. The hose is also almost totally straight from the strainer to the pump.
Bay Pines is almost straight inland from John's Pass Inlet between TI (Treasure Island) and Madeira Bch.
Thanks for your help and will keep all informed after I get further with this.... |
makomark
Senior Member
Username: makomark
Post Number: 2149
Registered: 09-2008
| | Posted on Sunday, February 07, 2010 - 06:10 pm: |
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Sounds like you really need to measure the raw water pump's output. That's the only definitive way to find out if the issue is upstream or downstream from the pump.
If the overheat is just with rpm > 1500, you can rig the dock hose to the raw water hose where the pump would normally provide cooling water.
Another item to check is the strainer gasket/lid...an air leak there will cause these types of issues. Another good check is that clear hose you mentioned. Put it between the pump and the fuel/oil cooler and watch what flows thru it. Anything other than a solid stream of water needs attention - aerated water doesn't cool very well. |
chiefalen
Advanced Member
Username: chiefalen
Post Number: 606
Registered: 03-2008
| | Posted on Sunday, February 07, 2010 - 06:27 pm: |
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Jeez i can't say i'm sorry enough Ghost, i thought we were all thru checking the exchangers.
I thought he was finished.
So i thought we would start lookin elsewhere. |
Pat Phelan
Member
Username: capnlazy
Post Number: 4
Registered: 01-2010
| | Posted on Monday, February 08, 2010 - 09:06 am: |
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Could a hose be collapsing on the suction side of the pump? |
Duskey
Member
Username: duskey
Post Number: 11
Registered: 01-2010
| | Posted on Monday, February 08, 2010 - 11:19 am: |
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Makomark, I swapped the pumps between engines, so I'm sure the pumps are good, the impellers are new; both pumps cooled the starboard engine fine.
A collapsing hose? I doubt it, as the input hose from the strainer to the pump is that very tough fiber reinforced hose I can't collapse it if I try. But, I can easily check for this when it's running.
I probably won't get back to this for a few days again, as when I installed the end caps on the heat exchanger one of them cracked in half, so I'll need to order another and wait for it, but in the mean time I'll check the strainer, valve, and plumbing. |
Duskey
Member
Username: duskey
Post Number: 12
Registered: 01-2010
| | Posted on Sunday, February 14, 2010 - 06:40 pm: |
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An update on my overheating/cooling problem. After re-installing the heat exchanger again and removing the sea strainer and cleaning it very well, no blockages. I put it all together and still had the same problem. In an effort to rule out the exchanger or just a pick-up problem, I connected a 1 ¼ inch hose to the pump and put it over the side of the boat, by-passing the pick-up. The engine now ran cool and neither exhaust manifold heated up. I'm now sure that the pick-up has a blockage. I can see the valve and sea strainer are fine, and the rest of the cooling seems to be good. I need to send a diver in to look at the outside of the pick-up, or pull the boat out of the water to examine. I’ll look into the price of pulling the boat out (probably about $200) or the diver. I guess I’d really like to see this for myself. Anyway, I believe I've got a very good knowledge of the cooling system after all this. Thanks for your continued help. |
chiefalen
Advanced Member
Username: chiefalen
Post Number: 625
Registered: 03-2008
| | Posted on Sunday, February 14, 2010 - 07:58 pm: |
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Pickup after all, first post to your question i asked about water coming in, oh well actually a cheap fix.
Keep us updated, good luck ! |
Duskey
Member
Username: duskey
Post Number: 13
Registered: 01-2010
| | Posted on Thursday, March 11, 2010 - 03:17 pm: |
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Finally got the diver in the water.....the strainer openings/slits were all bent shut/together.
The diver indicated he spread each one apart one at a time with a screwdriver..... I opened the valve and the water shot in through the 1.5 inch hole 3-4 inches high! The flow has been restored.
I figure if this would have been summer I would've found this much sooner.
Thanks for all your suggestions.
Now I can concentrate on rebuilding the steering cylinder. |
