Excessive oil consumption in my Yanmars?

[Captain Bill]

When I bought my boat my 2 yanmar 3JH3CEs had 525 hours on them and that was 8 years ago. They now have about 2100 hours. Ever since I've had the boat the engines have dependably used a quart of oil every 16 hours. Reading some recent posts this would seem to be a bit excessive compared to other's experience. Since this is my first diesel boat and as Captain Ron Said "Diesels love their oil", I really haven't had too much concern. The engines start on the first turn, even in cold weather. I don't ever see any smoke or oil sheen.

I change the oil twice a year or every 250 hours, per the manual. I think I only actually hit 250 hours once between changes. Since this has been constant since I've owned the boat, I don't think it's anything I've done to the engines. The only oil I've ever put in the is Rotella 15w-40.

Is this really excessive or should I ignore all the cruisers that say their engines never use any oil between changes?

[DeepFrz]

It certainly seems excessive to me. I would think 1 quart every 100 hrs. is more normal. I wouldn't be concerned at 1 qt. every 50 but 16 hrs. is a lot of oil to burn. Less than a day of motoring.

[sailorchic34]

It's a lot. Mine was using that amount, but I had a broken piston. Well a piston with all broken rings and two broken ring lands. But mine was HARD starting and had high blow by.

So with the engine running, pull the crankcase breather hose off, the one that goes from the valve cover to the intake manifold. It should be clear with no excess pressure or bypass. If you get lots of grey smoke out of it. It is most likely rings. Could also be a blown head gasket, which is good news as that at least a $1000 less expensive.

I assume you have checked the water tank">fresh water tank for bubbles and or oil. too. Bubbles or oil in the fresh water tank isa sign of a blown head gasket.

Could also be bad valve guides but probably not with that amount of oil consumption.

[Wraith_Mac]

Bill,
It would be worth checking the valve stem oil seals and caps.
Yanmar modified the inlet valve stem seals to part no. 124460-11340 yet the exhaust VSS have remained the same, 121400-11340.
I don't know specifically why they did this but usually a supercession involves an improvement in materials or design and therefore a need for same.
Just a thought,
Cheers,
Mac

[d design]

I would do a dry and wet compression test and go from there

[Wraith_Mac]

Originally Posted by d design

I would do a dry and wet compression test and go from there

+1
Never a bad thing.
Cheers,
Mac

[twinboat]

One other thing is if, you have an oil cooler, they can leak oil into the raw water, if it has a pinhole. Test that, before tearing engine down.

[Captain Bill]

Originally Posted by sailorchic34

It's a lot. Mine was using that amount, but I had a broken piston. Well a piston with all broken rings and two broken ring lands. But mine was HARD starting and had high blow by.

So with the engine running, pull the crankcase breather hose off, the one that goes from the valve cover to the intake manifold. It should be clear with no excess pressure or bypass. If you get lots of grey smoke out of it. It is most likely rings. Could also be a blown head gasket, which is good news as that at least a $1000 less expensive.

I assume you have checked the fresh water tank for bubbles and or oil. too. Bubbles or oil in the fresh water tank isa sign of a blown head gasket.

Could also be bad valve guides but probably not with that amount of oil consumption.

It was actually your rebuild thread that got me concerned. I've checked the coolant and never found any bubbles or oil. There is no oil cooler on this engine. I've had the heat exchangers apart twice for cleaning in 8 years and seen no sign of oil in the exchangers. I'll check the breather today. The engines have no trouble reaching their 3800 max RPM when the props are clean. I don't do it often but I occasionally run it up to max RPM as kind of a health check. I guess the good thing is that it hasn't gotten any worse in the last 1600 hours. I don't know how the previous owner used the engines or how well he did the break in. 525 hours in 3.5 years did not seem excessive. I mostly motor on one engine these days so I'm not building hours as fast as I used to. I never run more than 12 hours a side without checking the oil, and I'm down 3/4 of a quart when I'm running at normal cruise RPM (2950). On occasion I motor sail at 2500 RPM or less and at 12 hours I'm only down half a quart so the consumption is somewhat proportional to RPM. I'll let you know the results of the breather test this afternoon.

[a64pilot]

OK, if they are making good power, don't smoke and are easy to start, what's to fix?
The symptom of oil going past the valves via valve guides and seals is almost always excessive blue smoke at initial stat-up, you don't have that, do you?
What I bet you have is rings that didn't seat, if the proper cross hatch wasn't honed into the cylinders during overhaul, rings are very difficult to seat, or if everything was done correctly during overhaul and the engines were babied, the rings didn't seat.
Rings that haven't seated well will have excessive blow by, about the only thing that can be done to seat rings that have been is service for awhile is to tear the engine down and properly hone the cylinders. A lot of misery and money to fix just oil consumption.
Often running an engine at high manifold pressures will seat the rings over time, in other words, run them hard, don't overheat them, but high cylinder pressures will force the rings against the cylinder walls causing them to wear in or seat. This won't happen in a short time, but if the engines were run a lot at lower RPM and load, like being used to charge batteries for instance, that will not allow the rings to seat.
You want to load the engines up and run them hard, it's very common on new engines to put them on a Dyno and run them hard, to seat the rings, it's not so much a high RPM thing, it's actually a load thing that seats rings.
But back to my original sentence, if oil consumption is the only concern, I'm not so sure I would spend a whole lot of money on that, run em hard for a few hours first, of course keep an eye on temps and oil level, but I've seen many engines that don't break in until run hard

[djmarchand]

I agree with most of the comments. That the engines start easily from cold is a good indication that the rings are ok. Another is little blow by out of the breather tube. Don't bother with a compression test.

One long shot possibility- is your oil level right. Sometimes the dip stick gets marked wrong and other times an engine installed with a lot of fore and aft rake will not indicate properly.

If the oil level is down a half quart, does it still use oil at the same rate as when at the indicated level. If oil consumption drops off then the oil level may be too high. High oil level gets blown out quickly.

David

[Captain Bill]

Ok I'm reporting back. There was no smoke coming out of the crank case breathers. I opened the oil fill ports and shined a flash light through the area and could see no smoke, so I don't think I'm getting excessive blowby.

A64pilot: The engines have never been overhauled. They were in service 3 years and 10 months when I bought the boat and had 525 hours on the meters. On possible hint at previous use was that the lady the previously owned the boat pointed out that the engines were much more effective at charging the batteries than was the genset. The genset had 93 hours on it when I bought the boat. I may have put 10 hours on each engine charging the batteries since I've owned it and that was only because I nedded to do some charging when my genset died. I almost always run them at 2950 when motoring and 2300-2500 when motor sailing, so they almost always have a load on them.

The engines are saildrives, not shafts so the engines sit on the level. The book says the capacity is 5.5 liters. When I put in 5 quarts at an oil change the dipsticks read about 3/4 Qt(L) low. This would seem to indicate that the dipsticks are correctly calibrated.

Does anyone know of an easy way to check the valve seals or should problems be ovious from just looking at them?

[sailorchic34]

Well not too much wrong with the engine then. Could still be a stuck oil control ring, but just as likely to be intake valve seals or an oil leak at a front or rear seal or a leaky exterior oil line. But then you would see oil in the bilge. Hum, long odds would be a clogged crankcase breather.

[DeepFrz]

If the oil seals are bad you would likely see smoke out the exhaust. When you had the filler cap off did you notice puffs of air (gas) coming out the filler pipe? You may not have seen anything (depending on oil temp.) but you might be able to feel a significant puff coming out which would indicate blow by.

[Wraith_Mac]

Quite often when intake valve stem seals are leaking slightly no blue smoke can be seen when under constant load as the small amount of oil is combusted.
The easiest test I know is to run the engine/s under load at high revs, quickly reduce the revs to near zero, wait a couple of seconds then punch the revs up again to near max, watch for the tell tale puffs of blue smoke from the exhausts.
They may not be huge either.
If anyone has a better or more accurate method I hope they can chip in and advise you.
This is the best pictorial guide I could quickly find and I do know it's a gasoline engine but the principle's the same AFAIK.
Product & HowTo Info | | | INSPECT | AutoZone.com

Cheers,
Mac

[BriaF]

I have a cat twin inboard diesels
One used oil from new 1Ltr per 50hrs
I was advise to run it at full throttle
which would seat the rings.
I did this for 15min problem solved

I would advise you to try this before
pulling anything apart.
Possibly as long as 30min
The engine needs to run at redline
To be effective

I now run my engines at redline
10 min every 50hrs

I have driven trucks all day (10hrs+)
at redline. diesels can handle this

Hope this works for you