Yanmar 2GM20 oil comes out of dipstick hole after stopping engine

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crown22

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New to me boat and after ninety minutes running there was a strange single "crack" noise from the engine before normal service was resumed. An hour after stopping
decided to check engine oil level.Oil comes up and out of the dipstick hole and into the bilge.About a pint. Engine was supposedly serviced just before I bought the boat
and I now regret not servicing the engine myself.Crew suggested that the engine had been overfilled with oil?Occurred to me later that it might be diesel fuel in the sump?
Any ideas appreciated.Thanks
 
Was it running normally and during running you heard a crack or after stopping it and starting it again? How long did it run normally for after the crack?

Is the oil normal looking viscosity and smell? You could probably tell if a pint or more of diesel was mixed with it smell wise. If its runny but no diesel smell maybe water. If it hydro locked it could crack the cylinder but probably not run normally for long after.

Possible someone overfilled with oil though you'd think the level would be confirmed at some point in a service. You didn't check the level before running? Obvious thing to do is drain and refill yourself and hope for the best. If it happens again will need some surgery
 
Last edited:
crown22 said:
New to me boat and after ninety minutes running there was a strange single "crack" noise from the engine before normal service was resumed. An hour after stopping
decided to check engine oil level.Oil comes up and out of the dipstick hole and into the bilge.About a pint. Engine was supposedly serviced just before I bought the boat
and I now regret not servicing the engine myself.Crew suggested that the engine had been overfilled with oil?Occurred to me later that it might be diesel fuel in the sump?
Any ideas appreciated.Thanks
Click to expand...
Over filled or possibly the crankcase of feather locked or both. Anyone hope hvykh get soeted
 
Thanks guys I checked the oil level before using and the oil was not black but clear which I thought slightly unusual
because whenever I change the oil on my diesel car it goes black instantly. Because the oil was clear maybe I didn't read
the dipstck correctly.After the crack the engine ran perfectly.I kept the power to a minimum until I got on the mooring.
This engine doesn't have a rev counter so I was trying to take it easy on it's first outing.Old Harry are you talking about the crankcase breather?That rings a vague bell from my youth.Thanks again
 
bare in mind it could hydrolock with any fluid so diesel, water or oil. If a pint of oil flowed out of the dipstick tube later purely because it was overfilled it seems likely you'd have noticed it coming out when you checked it earlier. As anyone who changes oil by suctions knows it is significantly less viscous when hot so it might not have ran out when cold but surely some would have come up the dipstick tube if it was that much over filled. Unless it was a very quick check perhaps, literally out and back in, but as you questioned the colour I bet it was a few seconds pause, it would have come out.

Hydrolocking with cooling water from a head gasket fail is most common after a pause so the water can run in, when the engine is running the higher pressure is in the combustion chamber so it keeps the water out until its stopped (as far as I know). If there is a crack somewhere that leaks water into the lower part of the engine though?

The look and smell of the oil will give a big clue I bet. Let us know what it was when you find out. If theres a crack in the block surely the seller must have known, there are some proper w***ers about. If the oil was that clean maybe he'd flushed it through to get the mayonnaise out from previous water in oil so he could sell it.
 
Another thought - after the oil had finished coming out did you check the level? If its low it would be gas pressure forcing it out, if its still high on the dip stick then something adding to the fluid level
 
I can't think why oil would come out of the dip stick unless pressurized or over filled. Not over filled, as you checked it. So, check if oil, not diesel/oil mix. That it was clear, is a big head up. Like you, after any oil change on a diesel, the oil is black straight after.
The 'crack' is worrying..
 
Thanks Athompson and Downwest. I was a bit fed up and had to get off the boat before the tide went out otherwise
I would have been dragging the dinghy across the mud.I'm going back tomorrow the day after or the day after that. Definitely
no oil came out of the dipstick hole when I checked before leaving. Forgot to mention the black soot or oil on the transom noticed
on arrival at mooring .Everything went perfectly for the first seventy minutes of running and then the "clack" or "crack" and one of the crew
noticed oil or diesel on the water.Cut right back on the revs for the final ten minutes to mooring.Also forgot to mention that because of COVID I was using some three year old red diesel in the tank mixed with brand new diesel.Oh and by the way why do these engines not have a rev counter to discourage crew who are in a hurry to be re-united with their girlfriends? What a carry on I will report back and thanks again
 
Wouldn't be too down on the clarity of the oil. On my boat, especially if I have been really diligent draining the oil from the sump, the new oil looks rather clear for the first dozen hours or so, and only visibly black around thirty.

Other than that, nothing to add but watching with interest. Please let us know what you find.
 
When you get back to the boat re-check the oil level. If you've lost a pint then it should show lower on the dipstick now. If it shows the same, or higher, then you have fuel draining in to the sump (very unlikely to be water as you'd see emulsification in the oil). Capacity is approx 1.9lts.

Engines are more often overfilled rather than the reverse so that possibly could be the issue, especially if the crankcase breather is faulty - the cases become pressurised and so the oil if pushed out. The 'crack' may be unrelated if the engine continued to operate normally, but certainly warrants investigation.

Small diesels often have no tacho; they're governed to operate within designed RPM so there's little danger of it being pressed too hard. Tachos are useful though, especially if you're matching the engine to a new prop. Yanmar ones are wired to the alternator I think.
 
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