Overheating problem

I just put in a reman long block and it is running hot. It is a 1984, Crusader 270 (GM 350 block). Freshwater cooled. It runs around 160 at an idle, with or without the thermostat in. (It is now out) The faster you go, the hotter it gets, but it takes a couple of minutes to get up to around 200, at which point I throttle back, so I don't know how bad it will get. I replaced the impeller. One exhaust manifold was sometimes hotter than the other, so I replaced it. No difference. Raw water flows. Raw water filter is clean. Antifreeze flows back to the heat exchanger from both manifolds. (so I know both pumps are working and fluid is circulating everywhere it should) I have flushed everything I can and as far as I can tell both systems flow freely without obstruction.
I don't know what else to check or replace. Any suggestions? Does anyone know what the flow rate for the two systems should be? Is there anyway to pin down the source of the problem by measuring the temperature at various places, e.g. either fluid going in/out of heat exchanger?
I thought it might be the "new" block, but if there was some blockage in it that prevents enough flow at high temperature it doesn't make sense that not enough would flow through at idle to keep it cool then. Right?
In short, all components of the cooling system seem to be fine, it is just not quite pulling away enough heat from the engine.
I would appreciate any suggestions. Going everywhere at 6kts is getting to me.

did you use new exhaust elbows? Install the gaskets correctly? oil cooler's condition?

by all means, get an IR temp gun and measure things. You can use the search function and find several posts on this topic.

Assuming the reman house is competent, your issue is likely to be inadequate raw water flow...you need to make some measurements to find the root cause and then fix it. Also, put the thermostat back in...I'd bet omitting it will eliminate any warranty you may have.

Was the previous engine also running hot before it was replaced? As you will see when reviewing some of the various threads on this site for engines running hot, the fix could be an air leak somewhere in the water intake, a worn cam or back plate in the pump (you only replaced the impeller), a partially clogged oil cooler, a partially clogged heat exchanger (remove the end caps and check/clean the tubes), etc, etc. Do you have twin engines where you can swap one part at a time to try to isolate the problem?

Erich

I did not use new exhaust elbows, but did replace them a couple of years ago. Yes, I have had overheating issues before with that engine, which is why I replaced the elbows (but it didn't seem to make much difference at the time). The inside of the raw water pump (which is also only a couple of years old) looked shiny and new inside (as did the impeller, but I replaced it anyway). I disconnected the raw water hose coming out of the heat exchanger and there seemed to be a lot of flow. Since the flow from the disconnected hose seemed to be more than the flow from the exhaust (although I didn't measure either flow) I also ran the engine with that connection loose and leaking, thinking if there was a restriction in the elbow (or anywhere between the exhanger and the end of the exhaust) leaving it loose would increase the flow through the exchanger, lowering the temperature. It didn't seem to make any difference.
All gaskets are correct, as far as I know, but there isn't really any flow through that area anyway. The oil cooler is right after the raw water pump so if it was restricting flow there wouldn't be much coming out of the heat exchanger (which is downstream from the oil cooler).
Since letting the raw water leak didn't help, and the raw water didn't seem that hot coming out of the exchanger (i.e. hotter than I would shower in but not so hot I couldn't hold my hand in it), I am inclined to think raw water is not the problem. On the other hand, there also seems to be plenty of flow on the antifreeze side.
I didn't have any luck with the seach function (suspect I am doing something wrong). I did read the "similar threads" the site referenced below, but they were not helpful.
If I make meaurements of flow, or temperature, how do I use that information? (I don't know what they should be, so won't know if/where mine are abnormal.
thanks.

the raw water pump should give you at least 8 gal/min when spun at 1000 rpm with no head. it also needs to be clear (no bubbles) to cool adequately. if its low, there isn't enough cooling water to take the heat out of the HX.

The IR gun will give you temps at various locations in the cooling system "non-invasively"...if you have twins, you can use the 'normal' one as a reference to find the 'hotspot'...that will give you some insight as to where the trouble lies.

I went out this morning to try a few things. Measured water flow coming out of the exhaust (or attempted to by seeing how many seconds it took to fill a (two gallon?) bucket). At 1000 both engines took about 15 seconds. At 600 one was a little less than 30 and the other (the hot one) a little more than 30 seconds. It is possible that the hot engine flow was a bit less at 1000 too, the measurements were not precise. With both engines running about 160 the raw water in/out was running about 78/109 in the hot one, 78/97 (all measurements approximate average because I took mulitiple readings and they varied a bit), coolant in/out was about 170/120 and 166/108. I don't have a degree in phyics but it seems the only way the raw water could heat up more while cooling off the coolant less is if there is less flow. Since I trust the heat measurements more than the raw water flow measurements, I am leaning toward thinking I have a reduced raw water flow in that engine.
Now I just have to confirm that, then figure out why.

I had a very similar issue with one of my 502's. the issue was the oil cooler. at idle the engine ran fine at normal temps. Once we took it out and put the engine under a load she would overheat. What I did was remove the hose leaving the oil cooler and poured muriatic acid (available at any true value hardware store for under $3.00)into the oil cooler (remove the zinc before doing this) then replace the hose. wait 15 minutes and start the engine. you will probably see lots of junk flow out of the exhaust. this solved my problem and every year i repeat this on both oil coolers and have not had an overheating issue in years.
an old crusader tech once told me we boaters always startg at the wrong end of the cooling system when we have an overheating problem. we should always start at the intake, and work back from there. Seems to have been good advice.
good luck and let us know how you do.

Thanks for the suggestion. The cooler was clean in the spring when I installed it, but I will check it anyway.
I understand how a restriction in raw water flow would cause it to heat up at higher RPMs, but I don't understand why it would run hot (160+) at idle (with no thermostat). If there was so much restriction that there wasn't enough flow to keep it cool at idle, wouldn't it over heat very quickly at higher RPMs? (it doesn't, the temp climbs very slowly and it is clear that more raw water flows through at higher RPM so it would not seem to be a physical limitation).
Could it be belt slippage? It is tight and there is no whine that usally indicates a slipping belt but that makes more sense to me from the symptoms. Is there any way to check that (other than checking tension and listening)?

If the blockage is in the bottom of the oil cooler where the zinc is you can't see it. For the small investment of the acid, I would just do it and see how it goes

KAG: the oil cooler is a well known issue like bkair suggests...given its construction, how do you know it was 'clean'?

Also, the temp measurements are great but you need to better define WHERE they are taken from for any of us to help...tooo many inlets and outlets in a cooling system, on either side. Remember, you are there and we are not...those little details can make a HUGE difference.

I can't try the acid in the oil cooler until the weekend, because our hardware store closes at 5. But, I disconnected it and ran a hose directly from the pump to the exchanger (so nothing is going through the oil cooler so any blockage in it can't affect anything). (figured that was okay at idle speeds in neutral at the mooring) It ran about 5 degrees cooler. But, it still got up over 150, at idle, with no thermostat. So the cooler may be a contributing factor, but I don't think it is THE problem.
With hoses off both ends you can see through the cooler and it looks pretty good inside to me. I don't know of any zinc in the oil cooler. There is a brass (?) plug (similar to the one in the heat exchanger which has a pencil zinc in it) in it but there are no threads on the inside of the plug where a zinc would screw in.
While I was out there, I put a tee in the hose that runs from the exchanger to the exhaust. The idea was that if there was blockage in the elbow this would allow more flow through the exchanger. If anything it ran a few degrees hotter.
So, I don't think it is the elbows and don't think it is the oil cooler. The heat exchanger got a good flushing in the spring. The raw water pump seems to be putting out a good flow of water.
I can try and better describe where I measured temperatures, but I did it in the same places on both engines so the comparisions should be good. I think my heat exchanger set up was a bit of a selfmade thing by a prior owner but bascially, the readings were at the pipe fittings going into and out of the exchanger, both in and out and raw and coolant. None were made on the engine, manifolds, etc. (I did some there but didn't report them here, there didn't seem to be any useful information, they were very similar for both engines)
I appreaciate the responses and am willing to try just about anything as I am out of ideas.

DUH!!! The small blocks DON'T use the U-shaped (zinc piece trapping) oil coolers.

Is the 'bypass hose' you used on the raw water line clear? if so, any bubbles?

would you post a pic of the 'homemade" appearing heat exchanger setup? non-standard configurations are always a challenge...

Should I still do the acid thing on my (straight) cooler?
The "bypass" hose was not clear, but the one I used to connect to the tee was. No bubbles visible in (raw water) flow coming out of exchanger.
I will be travelling for work tomorrow so any pictures will have to wait.

It won't hurt to flush out the cooler but I would defer that task for now. I'd be inclined to get a clear hose on the output of the raw water pump

As for the belt, I had one slipping on a Crusader 350 due to an "equivalent" belt (not factory) being slightly narrower and bottoming out in the pully. If you can turn the water pump by hand then it is too loose. I found I could even when the belt felt tight. But in my case, the slip was only at higher RPM and your issue is also at idle.

With the correct belt, new pumps, clean heat exchanger, no thermostat and 78 degree seawater in, my temps were as follows:
After 10 minutes at idle: Oil filter 129, top of intake manifold by temp sender 106, Exhaust manifold coolant exit to heat exchanger 109
After 5 minutes at 3000 rpm (no load): Oil filter 142, by temp sender 107, Exhaust manifold coolant exit to heat exchanger 110
I don't have detailed measurements for underway at 3000 rpm but the temp sender was only showing about 130. I did put a pressure gauge on at that point and saw wild fluxuations due (I think) to cavitation issues of running the water pump without the back pressure of the thermostat, so the no thermostat option is not a good long term solution.

As you can see, if your numbers are accurate, this engine cooled a whole lot better than you are seeing. And there is (or should be) a huge amount of cooling capacity in your engine's cooling system and it does not seem to be there. So I agree that chasing flow problems is your best course of action at this point.

Good luck!
CaboJohn

CABO:

You need to put that t-stat back in there. Bad news running an engine that cold: moisture forms and then acid and then sludge.

Jeff

@Jeff Oh it is back in (with a couple of extra bypass holes). But I thought KAG might benefit from seeing the no thermostat temps he should be seeing if his engine had proper flow.

CaboJohn

The pump belt did not seem to be slipping but since it was replaced this spring I thought just maybe. I took the belt off the other engine. It ran a bit cooler initially at the mooring but heated up at higher RPM and did not cool down much (still over 160) at low speed ( 800-1000) on the back in.
No bubbles.
No idea what to do next.
Any suggestions? Please. Thank you.

Look for an air leak before the raw water pump. It doesn't take much to cause overheating.

Jeff

@KAG I'm not clear on whether you got an IR gun or not. They are about $60 on the internet and essential for finding overheat problems. When you get one, first be sure your sender/gage are accurate. The temperature of the intake manifold next to the sender should be within a few degrees of the read out at your helm. You would hate to find out a month from now your problem is a bad reading. Then use the gun to check temps at all points compared to the good engine to see if the bad actor jumps out.

As an aside, you will note from my temp readings in a previous post you look at least 50 degrees too high in the idle temp with no thermostat. That is a huge difference and if correct it would seem likely there is restriction somewhere in either the raw water or fresh water side, as others have advised. You will also note in my readings that higher RPM at the dock (no load) should not bring any real temperature increase. The additional fluid flows more than make up for any additional heat generated. This is not true when under load, however. 3000 rpm under load (pushing the boat) generates a lot more heat than any dock side test. It was not clear what situation you were discussing.

Any marine growth at the raw water intake or in the raw water filter? Can you do a test with the raw water filter screen out? Any possibility that the antifreeze mixture has exceeded 50/50? Antifreeze does not cool nearly as well as water so too much with definitely cause overheating. Some boaters with cooling issues run 25/75 or less antifreeze/water, some warm water boaters use plain water with an additive package thrown in to lubricate the pump and reduce corrosion.

Have you flushed the raw water system with fresh water? Have you checked to make sure the feed hoses to the pumps are not collapsing? The hose feeding the fresh water pump should have a wire coil in it to prevent the suction from collapsing it (I am not sure if this is true for the raw water pump). Have you checked to see these are in place (sometimes they move down to one end of the hose)? Have you taken the ends off of the heat exchanger to be sure you don't have minerals or crud that have built up that might insulate the coils containing the fresh water? In such a circumstance you might get flow from both fluids but poor heat exchange between them. I would ask if your thermostat is correct but you believe that you have the problem with or without. In my system it is essential it is a marine type with the bypass holes to get flow from the hot engine to the cold thermostat during warmup. But some older Crusader systems had some sort of trick bypass that the thermostat, when it opens wide, eventually blocks off when experiencing a high temp condition so all the flow goes to the heat exchanger. Someone else on the forum may be able to explain it, but I would think running the wrong type of thermostat as well as no thermostat could cause an issue in these systems.

I hope somewhere in here is an idea as to where to go next. Good Luck!

CaboJohn

I am guessing (because I don't know) that any scale could be taken off the same way I clean swimming pool stuff or shower heads. Buy a gallon of swiming pool acid (I have never found the type much matters) and put 2 or 3 "glugs" in a bucket of water (always add acid to water, not vice versa). Submerge the part and if it bubbles it is working. Most stuff cleans up in 20 minutes or so. Wear glasses.

CaboJohn

Repeated tests yesterday.
Raw water flow on the hot engine (HE) was two gallons in 18 seconds. On the normal engine (NE) it was 17 seconds. Both measured at 800RPM. That is less than a 6% difference. Given potential inaccuracies in timing and engine speeds I don't think the difference is significant, and certainly does not seem enough (if it is even real) to make one engine run so much hotter. Conclusion, the problem is not from low raw water flow (since both engines have essentially the same flow).
Inserted a section of clear hose between raw water pump and heat exchanger. No bubbles.
Temperature measurements were different from above, but lead to the same conclusion: raw water on the HE is not taking away as much heat as it is in the NE. (raw water is not heating up as much and coolant is not being cooled as much)
HE: raw in/out 80/100 coolant in/out 160/130 manifold near sender 150
NE: raw in/out 80/107 coolant in/out 180/122 manifold near sender 153
(Note: one of the exhaust manifolds on the NE was very hot, about 220, which seems to be raising the temp of the coolant going into the exchanger well above the engine temp. Engine temp is still fine on that one so a problem for another day. I did recently flush that manifold and flow through it seems fine so I don't know why it is so hot.)
I did not measure coolant flow rates. One engine has a thermostat, the other doesn't, which would make a comparision near useless and I don't really like the idea of messing with 160+ degree coolant. Also, it seems to me that if low coolant flow were the problem the coolant coming out of the exchanger would be cooled off more (a low flow would allow more time for heat be absorbed by the raw water, not less as per the numbers I got).
So the only thing that makes sense to me is that, somehow, dispite plenty of flow through the heat exhanger heat is not in fact being exchanged (or at least not enough).
CaboJohn suggested that possiblilty. I have a hard time believing that there could be scale or whatever that would affect the transfer of heat but not fluid flow. But, I guess the next step is to pull the exchanger and take it apart. (I couldn't do it yesterday because the Admiral decided to come out for the day so the boat had to stay operational.) Truth be told, it is a very small space and I am not looking forward to it but unless someone has another thought that is my next move.
Thanks again for the suggestions and imput.

the raw water measurement does NOT indicate you have adequate raw water flowing thru the system. It does indicate your raw water pump is in a functional state and the clear (bubble free) product means the intake system and pump are functional, too.

I would NOT be too concerned about the flow rate on the closed side...issues there are possible but not common.

you noted a hot exhaust manifold on the NE...did you get the IR gun on the exhaust elbows? A restriction there will limit the raw water flow thru the system (independent of what the raw water pump can deliver) and will show up as an overheat issue.

You can use the acid solution to flush out the HX without removing it...I'd be inclined to get the IR gun first.

makomark: Thanks for the response, but I am not sure I understand. I measured the raw water flow at the exhaust outlet (at the transom where it dumps into the ocean). Flow there, which is obviously through the entire system, was two gallons in 18 seconds, which is 6 2/3 gallons per minute (at 800 RPM). Are you saying that is not adequate? It is about the same as the other engine, which is fine. (Looking back I see that I didn't mention where I measured. Maybe you thought I measured the flow as it comes out of the pump, which could be different from what gets through if there is blockage downstream? If so, sorry for the confusion.)

The hot exhaust manifold is on the engine that is not overheating. I did measure the manifold (and everything else reported) with an IR gun. I did not measure the elbows. I don't know how much the raw water discharge cools the elbow but I suppose if one of them was blocked (I don't think it is) it could heat up from the exhaust and some of that heat could be transferred back to the manifold. The hot manifold appears to be a problem and I will have to deal with it at some point. For the moment I am more concerned with the other engine but I will check the elbows next time I am out.

The only way scaling makes sense to me as a source of the problem is if it is on the coolant side of the tubes, which I can't flush out in place because anything dislodged would go into the engine. I could run some acid through the raw water side if I disconnect the intake hose and put it in a bucket. Either way, much as I hate to, I think I have to open it up. Otherwise I will always wonder the story was.

Agree, you appear to have adequate raw water flow

You should be able to touch the elbows without a problem...though you won't want to keep your hand there for a long time...going on memory 130 deg F is about the upper limit.

The only way I know of scale building on the closed side is for the coolant to be poorly (if ever) maintained. Flushing that is easy once you have drained the coolant and capped the hose nipples. Scale buildup is much more common on the raw side. removing the end caps will permit inspection. They make a brush for cleaning the tubes though an acid bath will get a similar result.

Up before the dawn this morning to pull the exchanger and bring it home. Will take the end caps off tonight and let you know how it looks. Feels weird to hope it is bad, but at least then I would know what the problem is (I hope).

If it is, you may want to visit the local radiator shop...quite possible they can clean it, repair it, leak test it and painted for a reasonable sum. Just make sure they have experience and aren't learning on yours.

Thanks, but there is no local radiator shop. Oh, the joys of island living.

You've got two sides to this cooling system, as you know. The sea water side, and the E/G coolant side.

First, follow the sea water path, and make sure that all is clear, and as mentioned, there can be ZERO suction breach here.

This may also mean inspecting the manifold-to-riser sea water transfer ports, of which if restricted, will cause a diminished sea water flow.

Look for any interior hose de lamination. It's rare, but hoses can delaminate at the interior.
Make sure that all suction hoses are "collapse" proof. Wrong hose type, and the pump suction can collapse these causing additional restriction.

Look for crustaceans that have grown within the sea water path.
These enter when small, grow to size, and then die off leaving their shells behind causing a restriction to the sea water flow.


Look for worn thrust surfaces within the sea water pump. If the thrust surfaces are grooved or worn, the impeller will not function correctly.
If bad, consider replacing the belt driven sea water pumps with the crankshaft style pumps.
You'll get to eliminate one belt, and two pulleys, and it will make life much easier, IMO.
NOTE: this works only if you have the space in front of the engines.


Inspecting the sea water side of the H/E tube bundle is protocol, IMO.
You can gently push rods through the tube bundle as to clear them.


Next would be your engine circulating pump. This will be the GM pump on the front of the engine.
Long shot, but if the metal impeller is bad, it will prevent proper E/G coolant circulation.
With a Closed Cooling system, the short body Automotive version Circ pump works just fine, and will save cost.
You can purchase this GM pump for around $30 or so.
Your Closed System Marine engine won't know the difference unless you tell it.


And yes..., definitely run a correct temp range thermostat in your system.


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