Yanmar 3HM head leak

[garvellachs]

Our elderly Yanmar 3HM is leaking coolant slightly from the area around the head gasket edge on the inlet manifold side. It has only done 900 hours but dates from 1984 and was raw water cooled until 2008. I fitted a Martec fresh water cooling conversion.

I suppose I could put up with it if I knew it wasn't going to get worse, but it's messy, and it's annoying to have to top up the coolant regularly.

So the question: if I take the head off and try to sort out the leak what might I find? Could this be a corrosion problem - do 3HMs or 3GMs (they are similar) corrode at the head/block joint? Is it likely to be fixable by skimming the head lightly perhaps?

If corrosion is unlikely to be the culprit, I would hope that skimming the head (if necessary) and a new gasket should fix it?

Otherwise the engine runs starts and runs well, no smoke to speak of, stable temperature, coolant stays clean.

Thanks for any advice from anyone who's been there or thereabouts.

 

[savageseadog]

It's probable that the conversion has increased the cooling water pressure. The first thing I'd do is check what the pressure actually is, also ensure that it's running at the correct temperature, ie about 90 degrees. If it's leaking there's probably nothing you can do other than replacing the head gasket. I don't know about skimming, I doubt if there's any warping or significant corrosion.

 

[TQA]

I would hate to disturb this running engine. You say 5 years ago you say serious corrosion and that the engine was raw water cooled for many years. Unfortunately I do think that there is a pretty good chance that either the head or block is corroded [ maybe both ] and causing the leak. I suspect that the long term prognosis is not good as the leak my well get worse with time.

Skimming the head or block to a significant amount to deal with corrosion may result in the valves coming into contact with the pistons. It is possible to skim the pistons to deal with this on some types of diesel. It depends on the design of the piston crown.

If the cylinder head gasket is the old fashioned copper sandwich type you might get some benefit from using ' hylomar ' a sealant with the gasket. This can help. I know that the use of hylomar with other types of gasket is somewhat controversial.

You could try to reduce the pressure in the system by changing the radiator cap for a low pressure one. They range from 4 psi up to 15 psi in my experience.

You could also try some Holts Radweld, this again is a controversial treatment but does work on small leaks in my experience.

If it were mine I would try the low pressure + Radweld for this season and pull the head at the end of the season, being prepared for the possibility of a new engine if the damage was bad on inspection.

 

[NickRobinson]

Sound advice from TQA- That's what I'd try after trying getting the engine to working temp by running under load for a good while with the radiator cap off.

It may boil and throw water out but is equally likely to do not very much other than remove the pressure on your leak which may then stop. You may have a simple leak to the outside but if you have combustion gases bubbling up in the header you have more complex problems.

BTW (and like back pain, everyone's an expert!) I always sought out Holts Wondarweld (sic.) instead of it's stablemate Radweld. Wweld is a bit more rigorous but harder to find. Kseal on the other hand- might as well use brown sauce!

Any sealer will have more chance of working if you remove your afreeze and use plain water as the afreeze unhelpfully reduces surface tension and seeks leaks out. Replace afreeze after your leak is fixed by adding it to the gloopy sealer/water mix which can stay in indefinitely.

Nick

 

[garvellachs]

Thanks for the input. I'll fetch the head off at the end of the season, and look at the pressure meanwhile. Thanks for the tip re Wondarweld too.

 

[alahol2]

I don't think you are anywhere near it yet...
Our old Volvo developed a coolant leak into one of the cylinders and died. The water had carved a channel across the top of the block and there seemed nothing to do to fix it. Rather than lose the season's sailing I just blocked the offending waterway with high temperature JB Weld epoxy. The engine carried on working for the rest of the season with no obvious hot spots or problems. It would probably still be working (in that respect anyway) had I not replaced it the following winter.

 

[garvellachs]

A follow-up on my 3HM head gasket leak. I took the head off a few weeks ago and took it to an engine specialist in Sheffield who agreed that there was some marking where it had been leaking and slight distortion. He skimmed the head back to clean metal (valves and injectors still in it), tested the valves and cleaned out the passageways for £30 and I re-installed it with a new gasket. So far (70 hours or so) no more leaks. It was quite straight forward to do it, just time-consuming.

I got the name of the engine man from a local garage I have dealt with for 40 years: he said they always skim heads when they take them off, just to be sure they will seal when replaced. I'm guessing they took off about 5 thou maybe.

Thanks again all.