M30 overheating

[bradpb]

Recently my new to me sailboat with an M30 engine (5424 universal diesel) has began to overheat – that is the temperature is pushing 220 F.

I have taken a couple of steps to try and solve the issue with some, but unsatisfactory, success:

1) The Mechanical survey mentioned that my heat exchanger was need of repair. I did a bit of research on this and found that the unit that came with the boat was flagged as being on the small side at 2 inches. I replaced the exchanger with a new 3-inch unit. Disappointingly, I found that the new exchanger didn’t help keep the temperature in check, so I embarked on other avenues of investigation.

2) I checked the Flow of water through the heat exchanger – all is good. However, it seems that not much water is spitting out the exhaust. I inspected the impellers on the raw water pump – all looked good. I checked to see if there were any blockages by forcing water through exhaust system on the off chance this was the problem – none found.

3) Next I turned my attention to the thermostat. I pulled it out and threw it into a pot of water to see if it opened, and it did. However, I should have stuck a thermometer in the pot to see what temperature it opened – I’m expecting it to open at 160F

4) I thought that maybe the block water pump was maybe operating incorrectly but I was hesitant to remove it to check the impellers as I didn’t have a new gasket if the existing was not salvageable. I did take the belt off and give it a good spin listening for anything unusual and to see if the water drew down in the open Thermostat body – there wasn’t any unusual noise and the water did move when spun.

5) I decided to see how the engine would run without the thermostat - well it runs cold, 100 F.

So where am I:

1) I don’t want to run the engine at a cold temperature for too long. I could partially close the raw water seacock to restrict the cold water coming in and causing the engine temperature to rise – but that’s not really a solution.

2) I failed to notice if the Thermostat was mounted in upside down when I initially inspected – it does have a couple of 1/8 inch holes that do allow for some water to move through, presumably enough water would flow through the small holes to activate the thermostat if indeed it was mounted incorrectly.

3) I could measure the temperature that the thermostat opens and replace if it doesn’t open at the correct temperature of 160 – I think this is a long shot, but I guess it should be crossed off.

Anyways, if somebody has some suggestions feel free to ring in.
Thanks

[model 10]

Unless you are in almost frozen water the engine will heat up enough to run safely for a good while. You should be able to trouble shoot the problem knowing that with no thermo it will not overheat even at full power.

[bradpb]

Thank you for your response Guy - I though the same but I motored for a few hours and the engine temperature never got above 100 deg F. The water in my area is quite cold - 60 deg F.

[model 10]

so 80 deg water would be 120. I can get 140+ in 85deg with no thermo. Sounds like you are good core engine wise.

[DeepFrz]

Does your thermostat have a small hole through it? It should have about a 1/16" hole. This will allow a small flow of hot water through the hole and will activate the thermostat. Some thermostats don't have this and they never open properly.

[Pete7]

I wouldn't bother measuring the thermostat, I would just pop a new one in and a new raw water pump as the same time and take it from there. Cost minimal and removes two possible problems in one go.

[bradpb]

DeepFrz, yes it does have a hole through the thermostat, two to be exact about an 1/8 inch.
One of my thoughts is that if indeed the thermostat was mounted incorrectly and that the business side of it was not getting any hot water, even with the two holes, because the pump was just not in good enough shape to move the water effectively - but this is pure speculation from me an non-mechanic.

[DeepFrz]

Have you checked the injection elbow to ensure it isn't partially blocked?

[bradpb]

Pete7, I believe that the Raw water pump is operating correctly;

[bradpb]

DeepFrz, I forced water through it and it came out the end in a rush.

[jimbunyard]

Well, if it runs cold without the t'stat and hot with it, check again that the tstat opens fully and at the right temperature. Simplest things first, accurately and methodically done, always seem to work best...and save money.

[cherylca]

I assume that you have controlled that you have your heat exchanger filled properly with the anti-freeze used in this closed part of the system.

After you check or replace your thermostat, and you are still overheating, do not assume that the exhaust pipe (might be elbow shaped) out the back of the heat exchanger which leads out exhaust and raw cooling water is not causing the problem. It could be sufficiently blocked to cause problems, incl. severe pressure build-up in the heat exchanger chamber to eventually cause serious problems more proximally in the engine, for instance blown gaskets ----EVEN IF you see water coming out the back of the boat. This exhause pipe ( elbow shaped pipe) has a limited life and needs to be replaced every 6-7 years
.

[a64pilot]

Originally Posted by jimbunyard

Well, if it runs cold without the t'stat and hot with it, check again that the tstat opens fully and at the right temperature. Simplest things first, accurately and methodically done, always seem to work best...and save money.

This makes the most sense to me, and I trouble shoot one at a time, or you never know what the problem was, but if it runs cold without a T stand and hot with it in, it sure seems to indicate a bad T stat.
May be someone put in a 195 degree auto T stat? Ought to have the temp number stamped on it though.


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[a64pilot]

Usually an inadequate cooling system will operate fine, at cruise power and won't overheat until the engine is run hard for quite awhile, but a bad t stat will cause overheat at cruise RPM.
What does it take for you to see it running hot?


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[MarkSF]

Two points :

1) You mention not much water is flowing out of the exhaust. This cannot be caused by a faulty thermostat - that affects the fresh water circuit only. The most common reason is that the exhaust elbow is blocked. However, the best thing is to measure the flow. I use a bucket under the exhaust. You should get about 2 gals per minute at 1500 rpm, maybe a little less if you have an Oberdorfer raw water pump. 2 gals is for the Sherwood.

2) The engine overheats with the thermostat in, doesn't with it out. Time to replace it. The thermostat in my 5424 didn't close properly, or open fully. I bought one for the Kubota tractor engine for about $10 on Ebay.

My experience is that with the 2" heat exchanger, the cooling is very marginal and anything non-optimum (exhaust elbow slightly blocked, raw water strainer not clean, and so on) the temps start rising, and 220F is quite possible.

With the 3" it simply sits at 170F always, even at full throttle.