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Old 25-08-2012, 16:00   #1
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Sustainable? Diesel Engine Blowby

I am attempting to get up the nerve for final acceptance of a sailboat after survey and inspection. Survey revealed nothing surprising, but after the sea trial there was oil in the bilge. Surveyor discovered it was coming from the dipstick. He reseated the dipstick and we ran the motor at full power (though in neutral) for a few minutes and the dipstick stayed seated. He concluded he did not reseat it firmly after the pre-flight check.

The surveyor said that this degree of blowby was common in an older diesel, and gave anecdotal experience of motors he'd lived with for many years in a similar state. He didn't call it out on his report as a major finding. He is very well respected and has very impressive experience. The only thing I question about his judgment is his being quick to assume that he didn't seat the dipstick well, because he seemed to perform every small task in routines established in accord with best practices. He was that sort of guy.

A compression test was beyond the scope of this general survey, but the engine ran strong and the boat made good speed.

I like the boat and would like to proceed, but not if an engine rebuild is eminent, or I have to constantly fear the dipstick backing out on its own and losing all the oil into the bilge.

Engine is a Universal M-25XP, 1987, 1500 hours. Good news is this motor should be among the cheapest to overhaul when the day comes, as it is based on a Kubota engine.

I'm trying to line up a mechanic for a compression and crankcase pressure measurement. I don't expect anyone has a crystal ball and can forecast how many months the motor has to live. What I'm seeking to confirm here is that piston ring blowby does not generally portend a swift decline, and it is not unreasonably optimistic to expect a few happy years of light duty. I do know there could be other reasons for the oil coming out the dipstick; a clogged breather or overfilling. Let's just assume it is worn rings, for sake of argument.

Can the community share experiences with motors in a similar state, whether they align or conflict with the surveyor's experience? Were you able to squeeze long service out of them, despite perhaps less than optimal efficiency and performance? Can I lash the dipstick in place if it pops out again, and go about my merry way?
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Old 25-08-2012, 16:36   #2
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Re: Sustainable? Diesel Engine Blowby

Greetings and welcome aboard the CF, Saqqara.

Your surveyor’s explanation sounds “plausible” to me; but further investigation (Leak Down & Compression) may be justified.
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Old 25-08-2012, 16:58   #3
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Re: Sustainable? Diesel Engine Blowby

Thank Gord.

Spoke to surveyor again, he said he put his finger over the dipstick hole and only felt any air escaping when engine was at full throttle. He continues to be reassuring.
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Old 25-08-2012, 17:04   #4
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Re: Sustainable? Diesel Engine Blowby

There are two things that I would require as a must do at this point.

1 - Drive the boat again and see if the fault repeats.

2 - A differential compression test. If your engine guy doesn't know what that is find a new engine guy.

Some leakage past the rings will always occur. Especially at high throttle settings.

I would not be overly concerned as the explanation sounds plausible but I would definitely run this to ground before I paid the money.

An engine with bad compression can last a year or a week - You won't know.

PS - I don't know what relationship you have with this surveyor but without offending him I would get a second opinion - i.e. engine specialist.
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Old 25-08-2012, 17:39   #5
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Re: Sustainable? Diesel Engine Blowby

I think a compression test and oil analysis should be routine in any assessment of a boat engine and gearbox. Try to find a good diesel fitter. Your surveyor is unlikely to be a diesel fitter, and should not be offended at your bringing one in.

its important for your diesel man to test compression at dead cold , and observe engine startup from dead cold...thats when problems of hard starting/low/uneven compression are most evident. Oil samples should be taken hot, with the oil well circulated. In my view, oil analysis can tell an enormous amount about the state of an engine. Test the gearbox oil as well.

As other posters have said, depending on the results above, I would not be unduly perturbed about how the survey went, from your description.

Lee
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Old 25-08-2012, 19:02   #6
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Re: Sustainable? Diesel Engine Blowby

+ 1 for banjos statement !! right on the Mark
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Old 25-08-2012, 19:03   #7
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Re: Sustainable? Diesel Engine Blowby

SORRY banjoship !!
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