Overheating problems in H37C Yanmar

[emilbec]

I am the owner of a 1981 H37C. The Yanmar QM3 was originally raw water cooled and lately after running for two hours at 2000 rpm overheats. I had everything checked and it seems there is corrosion in the engine block which is restricting flow. Any ideas other than repower.

 

[Benny]

I would think you need to go further. Open up the engine by removing the cylinder head. This will expose the head gasket as well as the cooling passages in both head and block. A thin and long, flexible wire brush can be used to clean out cooling passages. A new head gasket should be installed when reassembling the engine. In extreme cases the cylinder head may need replacing. If the problem lies in the block then you may consider repowering but with the knowledge that you have exausted your possibilities. Make sure the thermostat has been thoroughly tested and that it is opening and closing propely at the prescribed temperatures. Good luck.

 

[Steve Dion]

I would try some Oxalic Acid first. Just get some powdered Oxalic acid and put it in a bucket with water (couple of gallons). Use the raw water intake to suck it into your engine and let it sit in the block for an hour or two. Restart the engine and try that out.

The real stuff was called Marsolve. I do not know if it is still available, but this was what was originally used to flush out the raw water passages in a raw water cooled engine.

Here is the stuff that is supposed to replace Marsolve, it is callled Rydlyme.

http://www.rydlyme.net/index.htm

 

[Ed Schenck]

When you say "everything" was checked did that include removing and examining the exhaust elbow? That is generally the source of corrosion and restricted water flow. Were you present for the work and confident that nothing was missed? I just never heard of repowering for that reason.

 

[kloudie1]

There was a note on the 2 QM recently that may be relevant..?? There is a cover plate on the aft end of the cylinder head that can be removed and some of the cylinder head water jacket cleared with a probe and/or rifle cleaning brush.. Search on overheating and you’ll find it.. Don’t know if the 3 has that same plate, but it probably does.. I’d pull the head only as a last resort.. but if you do, you should be able to probe out most of the water jacket in the block and head.. Let us know what ya find..

 

[sailbode]

I think Steves idea sounds great. I'll be keeping that one tucked in my good idea folder!
D
PS: Hi Steve< it's been a few years

 

[txmilke]

<snip>
Here is the stuff that is supposed to replace Marsolve, it is callled Rydlyme.
</snip>

Hi emilbec,
I have a jug of the Rydlyme that you're welcome to if you want to go that route. I had symptoms similar to yours on my Renault RC8D that turned out to be an obstruction at the outflow to the exhaust manifold. Never needed to use the Rydlyme and don't know what to do with it.
I'm in Mayo and could leave it out if you want to pick it up.
Tom
txmilke@aol.com

 

[Bill Roosa]

check the heat exchanger

Pull the input end of the raw-fresh water heat exchanger. any little rubber bits? or scale?