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Discussion Starter · #1 ·
Yanmar 2GM raw water cooled with 900 hrs suddenly started leaving a sheen on the water out of the wet exhaust. Confirmed it was motor oil, not diesel, as I was losing 1qt every 30 mins. Will put out noticeable and sheen large billowing clouds of while smoke @ idle & while in gear @ ~2,500 rpm cruising @ 5 knots. Though, NOT smoke when taken out of gear and run up to ~3000rpm, yet still spews out sheen from exhaust.

Motor will run through all 2 qts in an hour. Though luckily have not sounded the alarm or over heated while trouble shooting.

No trouble starting or loss of power. At the rate of oil loss seems like turbo or oil cooler failed—-neither of which are installed. Mixing elbow has been inspected and found no issues and was replaced. No leaking into the bilge or milky oil.

Could this be piston ring failure?
 

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Could this be piston ring failure?
yes it could be.
But it could also be valve stem seals, or broken or burned valve, etc. Combined with white smoke, it certainly points towards a head gasket failure .... either as the root cause or as a contributing cause. I'd start with a compression test to get an idea of what is going on, it wont conclusively answer all questions but you could at least rule out (or in) the rings as contributors to this.

2qts/hr is a hell of a lot of unburned oil, so much so that I'd fear that "diesel run away" is a real possibility. I would not run her to hard or for too long in this state until you can get to the bottom of it.
 

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Oil leaks into the combustion chamber upwards from the sump/ crankcase ( caused by worn rings or very badly worn or scored bore or both)

Oil leaks into the combustion chamber downwards from the rocker/ valve gear ( caused by worn valve guides.)
Once it is in the combustion chamber it combusts,
This results in blue smoke with a clear odor of burnt oil.

You have a lot of oil being pumped out the exhaust without being burnt.
So oil is mixing with the cooling water and exiting by the exhaust.
As Bristol has suggested the likely cause is the head gasket.

This is not a put off till later job.
If the oil is leaking into the seawater coolant passages, there is a very high chance that seawater can leak into the oil passageways and into the crankcase and other parts of the engine.

Step 1 is to drain the seawater from the engine.
Step 2 is to get hold of a new head gasket and fit it.
You will find plenty of assistance on youtube.
NOW!!!

Gary
 

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I've got a 2GM20F that has some hours on it and burns a little oil. But what you describe is well addressed immediately above - 2 quarts in an hour; you have a material failure (head gasket most likely). That said, if you are going through the trouble to pull the head to replace the head gasket, may as well get the head checked (valve guides, vale seats. Won't address the piston rings unless you want to pull the block. But these yanmars do tend to keep ticking if you give them proper attention. Offered from the old adage that you don't replace one brake on your car if it has a problem, you replace all four to just get the job baselined. But then your bank account and if you are married, your spouses thoughts...
 

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If you found that the exhaust elbow or connected hose had what appeared to be standing, or not burnt oil in it, then you may want to pull the valve cover and inspect the area where the pushrods pass through. It is a common fail point when a hole will develop and allow oil to drop directly into the exhaust manifold passage of the head, bypassing the cylinder. There would also be evidence of the hole by examining the smoke coming from the oil fill hole while running. It is often confused with piston ring wear but piston ring wear doesn't allow for the passage of oil to the exhaust.
 

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Discussion Starter · #6 · (Edited)
I removed the head today and found a large hole thru to the elbow. I imagine far to large to repair- will look for a replacement.
139723

139729

139730
 

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Have to wonder why so many holes.
 

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Exhaust elbows are a wear item. No point repairing, they will wear through elsewhere. Time for new.

After market stainless steel elbows are sometimes less expensive and last longer.
 
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