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Old 23-12-2020, 14:50   #1
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Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

I am doing research in old threads and elsewhere but I'd like any ideas you guys might have.

My Yanmar 3JH with 6500 hours has been running fine since earlier this year when I changed the rear main seal and the oil pressure has been fine since I changed the oil pressure sending unit (and installed a secondary mechanical gauge).

Today when we advanced the throttle to 2500 to motor up the coast we got massive smoke (oil smoke, not steam, not carbon) out the exhaust. Of course we slowed to idle.

We found oil had also flowed out the dipstick, the oil level was down about 1/2 quart, and clean.

But oil pressure was OK, and at low speeds there was no smoke and no oil loss out the dipstick or anywhere else.

Advancing the throttle again the problem re-occurred and now the oil pressure became low, almost zero.

During all of this the engine continued to sound perfect, smooth (as smooth as any three cylinder engine sounds) started easily, idles smoothly. No excessive or strange noise.

I thought of a broken ring allowing oil to be burned or a damaged valve guide allowing oil to go down the valve, but neither of these would result in loss of oil pressure.

So we're back at the dock. My plan for next moves is to check the oil breather system, remove the injectors and check for low compression or an oily injector.

Any other possibilities?
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Old 23-12-2020, 16:53   #2
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

The probability that you have lost a lot of oil (from a relatively small reservoir) would possibly explain low oil pressure. Check that first to at least give a little comfort

High crankcase pressure is never a good sign but that it is happening with no disturbing noises is a puzzle. A damaged valve guide would not create such pressure, a broken ring(s) would but both would have audible indicators.

Have wracked my brain, canít think of a condition that would combine all those symptoms. Good luck.
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Old 23-12-2020, 16:59   #3
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

Quote:
Originally Posted by CassidyNZ View Post
The probability that you have lost a lot of oil (from a relatively small reservoir) would possibly explain low oil pressure. Check that first to at least give a little comfort

High crankcase pressure is never a good sign but that it is happening with no disturbing noises is a puzzle. A damaged valve guide would not create such pressure, a broken ring(s) would but both would have audible indicators.

Have wracked my brain, canít think of a condition that would combine all those symptoms. Good luck.
Oil level is OK (down about 1/2 qt from full.)

We completed a further inspection including crankcase breather system, and conducted a test run (at the dock). Up to 3000 RPM, symptoms not repeatable. Engine runs fine , smooth and quiet. No smoke, no oil loss, and reasonable oil pressure.

We will run a sea trial over the weekend.
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Old 24-12-2020, 14:20   #4
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

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Oil level is OK (down about 1/2 qt from full.)

We completed a further inspection including crankcase breather system, and conducted a test run (at the dock). Up to 3000 RPM, symptoms not repeatable. Engine runs fine , smooth and quiet. No smoke, no oil loss, and reasonable oil pressure.

We will run a sea trial over the weekend.
Sounds frustrating. Oil rings can be shot or cracked without making any noise.

Did you test it under load at the dock? Perhaps under load and with the boat rocking, there is enough additional oil splash to get some blow-by-aided oil loss out the breather?

Could your injection pump be malfunctioning (drifting or shifting out of time?), so that you are running rich and thinking the smoke is crankcase oil rather than excess fuel? Could the stop collar on your dipstick have slid, so that you are overfilled when it is reading full? Something flopping around in the air filter housing causing intermittent high vacuum?

You have no doubt tried to correlate this with anything that has been done to the engine recently. It sounds like a sudden onset. At 6500 hours, the engine is probably overdue for a rebuild... but the onset of blue smoke from loss of ring tension would have been gradual.

Wish I could help.
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Old 24-12-2020, 14:26   #5
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

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Sounds frustrating. Oil rings can be shot or cracked without making any noise.

Did you test it under load at the dock? Perhaps under load and with the boat rocking, there is enough additional oil splash to get some blow-by-aided oil loss out the breather?

Could your injection pump be malfunctioning (drifting or shifting out of time?), so that you are running rich and thinking the smoke is crankcase oil rather than excess fuel? Could the stop collar on your dipstick have slid, so that you are overfilled when it is reading full? Something flopping around in the air filter housing causing intermittent high vacuum?

You have no doubt tried to correlate this with anything that has been done to the engine recently. It sounds like a sudden onset. At 6500 hours, the engine is probably overdue for a rebuild... but the onset of blue smoke from loss of ring tension would have been gradual.

Wish I could help.
Thanks for the suggestions. I will follow up on all of them.

Right now I am of the mind that since it is not repeatable (at the dock) I think maybe the cyls and rings are sloppy and full power when hardly warmed up (5 mins at idle) allowed excess blow-by.

Will try it this weekend outside the marina.

Low (zero oil pressure is certainly a separate issue since the mechanical gauge shows decent pressure, the electric gauge has a wiring issue I think,

Again thanks for the ideas.
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Old 24-12-2020, 14:29   #6
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

Oil pressure bypass valve acting wonky?
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Old 25-12-2020, 06:29   #7
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

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Oil pressure bypass valve acting wonky?
Yeah, I've been wondering about that. I just can't imagine the scenario where it would cause the symptoms of smoke and oil overflow.

I haven't a clue how to test it. I once had it out I think about 9 months ago, and it seemed clean and the spring was not broken.
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Old 25-12-2020, 07:38   #8
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

This is probably a long shot, but have you had your oil analyzed? I had a similar problem and it turned out that my lift pump was leaking fuel into the crankcase, diluting the oil. That made the engine lose oil through the seals. New pump fixed the problem.

Good luck, Bill
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Old 25-12-2020, 08:05   #9
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

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This is probably a long shot, but have you had your oil analyzed? I had a similar problem and it turned out that my lift pump was leaking fuel into the crankcase, diluting the oil. That made the engine lose oil through the seals. New pump fixed the problem.

Good luck, Bill
Yes, thanks for that suggestion. I've had that problem previously, once from a pinhole leak in the fuel pump diaphragm, once from a defective injector which was dumping excess fuel into the cylinder which got past the rings into the sump. Both years ago.

In both cases the presence of fuel in the in the crankcase oil was easily detectable; the oil became thin, smelled of diesel, and the crankcase filled up. You can pinch the end of the dipstick and feel the viscosity and stickiness.

There is no outfit here to check the oil but I can watch for those symptoms myself. So far, this time, they don't appear to be present.
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Old 25-12-2020, 08:07   #10
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

Possibly a stuck ring, rather than broken. Sometimes carbon buildup in the ring groves can cause the rings to hang up in a "compressed" state, allowing blowby and oil consumption. Sometimes rings unstick themselves... I'm trying to imagine a scenario with enough blowby past stuck rings that it foams the oil in the sump and/or causes the oil pump to cavitate thereby also causing low oil pressure and a pressurized block... seems unlikely, and even more so that it would fix itself.

The other possibility I can dream up is a cracked block between an oil passage and a cylinder, opening up due to thermal expansion of the block when the engine is hot/under load and closing again when it's cooler. I don't recall if that engine has sleeved cylinders or not. If sleeved, then this is very unlikely.

Please let us know what you find!
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Old 25-12-2020, 08:12   #11
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

I was goingto suggest maybe a stuck ring also - could be that if symptoms intermittent?
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Old 25-12-2020, 09:44   #12
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

Quote:
I thought of a broken ring allowing oil to be burned or a damaged valve guide allowing oil to go down the valve, but neither of these would result in loss of oil pressure.

So we're back at the dock. My plan for next moves is to check the oil breather system, remove the injectors and check for low compression or an oily injector.

Any other possibilities?
A broken ring could account for pressurizing the crankcase and oil smoke out the back but it should do it all the time. A stuck ring can account for your symptoms but again not just at high RPM, it should be across the range with more the faster you go.

A clogged breather vent can account for all your symptoms as at high RPM you can actually keep the oil that goes to the top of the engine from flowing back into the crank case. Puking out the dipstick is a classic symptom of too much crankcase pressure. Excess crank case pressure can be the result of a clogged breather system or poorly sealing rings. Very minor possibility that a head gasket could do this but if it were a head gasket issue there are usually other symptoms. Compression test would be helpful in regards to head gasket integrity.

A leak down test would be the best diagnostic tool if looking at the breather trap and vent system do not reveal the source of the problem.

Knowing what the pressure on the crankcase at various RPMs would also be helpful information. It should be close to zero at idle and at max under 2psi with about 1 to 1.5PSI about right.

I assume when you back off to 2000 RPM or less the smoke out the back eventually goes away and the oil pressure comes back to normal?
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Old 25-12-2020, 10:55   #13
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

Scuba seas is correct. Make a simple manometer and the crankcase pressure will tell you a lot.
Merry Christmas.
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Old 25-12-2020, 13:23   #14
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

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Yeah, I've been wondering about that. I just can't imagine the scenario where it would cause the symptoms of smoke and oil overflow.

I haven't a clue how to test it. I once had it out I think about 9 months ago, and it seemed clean and the spring was not broken.
Yes, I have a hard time imagining it too. However, here is a far-fetched possibility: the underside of pistons are oil-cooled. The relief valve fails open from a piece of crud under the seat. (or it it is poppet type, from crud between the poppet and its little cylinder) Pistons overheat, going out-of-round. Lots of blowby, and lots of oil smoke. Relief valve eventually reseats, problem disappears.

Clogged cooling passage causing something that should be round to go out of round.

Key for oil pump rotor sheared: enough slippage causes micro welding making is just barely work again... naah...

As someone else suggested, a leakdown test might reveal a lot. One cylinder significantly different than the others would be worrisome. You can play with (keep fingers out of the way) different positions of the engine, so that different locations on the cylinders are sampled. You probably have a lot of wear at the top of the cylinders, (and little at the bottom) so the readings on cylinders can be suspiciously different, depending upon piston position at the time of test.

With high hours, piston rings can have very low wall tension from simple wear -- the end gaps in an old engine can be very large, meaning the cylinder is not squeezing the ring with much force.

Worth considering that the two issues are not causally related.

Is your temperature gauge reliable?

I like to imagine that there will be a solution that, once revealed, get's the Oh!!! Of Course!! reaction.

If it's any consolation, we all feel your pain. I hope your Christmas has been merry in other respects.
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Old 25-12-2020, 14:13   #15
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Re: Low oil pressure-Heavy Blow by causes oil loss-and Smoke!

[QUOTE=wingssail;33047

So we're back at the dock. My plan for next moves is to check the oil breather system, remove the injectors and check for low compression or an oily injector.

Any other possibilities?[/QUOTE]

I think till those are done we are just wagging. But the loss of oil pressure and then its return seems a separate problem to me. If you really lost oil pressure the engine would be toast now.
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