Oil Leak

Hermit

Hermit

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Hello,
As forewarned is forearmed can anyone give me some ideas of what may be wrong before the engineer comes tomorrow...

Yanmar 20GM20 raw water cooled. Within about 30 minutes of running (on the mooring but in gear) all the oil in the sump goes. I suspect it is going into the exhaust as there are traces of oil in the outlet water and lots of white smoke. Engine has not been used much over the past 18 months or so. Last time it was run I had a short duration overheat/no water which I suspect was an external blockage to the sea water inlet. Plenty of water in the exhaust now.

A phone call with an engineer has ranged from problem with the oil cooling system to bust head gasket (there is no water in the sump) to damaged head.

Any ideas would be helpful so I can ask the right questions of the engineer.

Many thanks,
Rob
 
I don't know your engine sufficiently well to point a learned finger, but suspect a gaskit. No doubt your engineer will check out in sequence before engaging in heavy engineering.

Suggestion for the future - engines do seem to love being used, perhaps a little more often that has been the case...?

PWG
 
That oil's go to be going somewhere so if it's not in the bilge it's either being burnt or getting out into the exhaust. Generally oil mixed with diesel will create a black smoke, rather than the white you mention, but a cracked head or gasket does seem the most likely cause. And the finger of suspicion is bound to fall on that short blockage you mentioned....
Good luck sorting it out.
 
Don't forget to take your cheque book - this is going to cost a bit!

I can't think of any simple explanation for this one and freely confess it's a new one to me. I have some doubts about it being a failed head gasket as I don't think the oil loss could be that fast. Losing litres of oil in half an hour requires quite a flow. And I would definitely have expected the smoke to be black, not white if it was being burnt. The only explanation I have is a crack somewhere, the block seems more likely than the head, so that oil is being driven at pressure into the coolant and out through the exhaust. With a fresh water cooled engine the flow would be the other way, i.e. water into the sump, but low raw water pressure could probably allow oil supplying either the bearings or rockers at supply pressure to flow into the water.
 
My Yanmar 1GM10 emptied its oil into the bilge in about 30 minutes at the start of last season. This was due to a tiny hole under the oil feed pipe, caused by corrosion, where it passes below the water pump. The engine was only 2 years old but when I raised it with the Yanmar agent, I was told it was a very common problem! The solution was a new transfer pipe.
 
As has already been said, the oil has to be going somewhere. If it's not in the bilge and not being burnt in the cylinders it looks as if Vyv's prognosis of a crack in the block is the favourite. If that is the case ( and I hope it turns out to a simple fix) it might be worth weighing the potential repair cost against a re-powering option,
 
The oil isn't going into the bilge. Could it be going past the piston somehow and through a faulty exhaust valve? Suggestion from elsewhere...
 
I can tell you without a doubt that there is a corroded hole going betweet the exhaust port and the pushrod cavity.
It is a very common fault with the head on this engine and is caused by exhaust elbows inner wall disintergrating and allowing the water and corrosive stuff back into the head. the engine oil will disapear rapidly.
The same happens on 1gm10 engines as well
 
Steve, what is the prognosis for a repair on this - possible, unlikely (undoubtedly expensive?
 
Agreed, head corrosion is a strong possibility, but I would have thought that a litre or more of lub. oil passing to the exhaust in 30 mins. would create a very visible slick, not just traces. Perhaps grasping at straws to explain a most strange problem, is it possible that the rear crankshaft oil seal has failed in a big way? I think there is a drain hole, but this might be blocked. The fly- wheel housing has a screwed plug for the tacho sensor, if fitted. This would provide easy viewing to see if the flywheel etc is heavily coated in oil.
 
<< Could it be going past the piston somehow and through a faulty exhaust valve? Suggestion from elsewhere... >>

If it passes the piston it will burn, causing clouds of black smoke. Remember Ford Anglias and early Escorts that frequently suffered burnt pistons due to ring seizure? Clouds of black smoke for miles.
 
Having just substituted

A 3YM20 for the 2GM20, I can make a shrewd guess (especially if yours is raw water cooled) as to the problem.

It's a leak from the pressurised oil-gallery into the cooling water jacket.

The GMs are notorious for head gasket blows (mainly because the bore has been increased over the years in an attempt to upgrade the engine) because of the minute lands between water and oil channels.

Rectification might just involve a new head gasket or, more likely, milling the head to get rid of a burn-score.

Don't leave it, salt-water in the bore leads to corrosion and pitting of the cylinder wall.

I changed the gasket on mine about 3 times over it's 18 years of hard work - the only reason I got rid of it was because it desperately needed a re-bore, and was blowing oil through the rear seal.
The cost of parts only for rebuild, excluding gearbox, was about £1700 (doing all the stripping and assembly myself) and a new engine, with new gearbox, was <£3000. For that one got new mounts, new gearbox and 21% more torque as well as a balanced engine.
All vertical twins are basically a buggers' muddle.
 
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