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Old 11-05-2021, 10:11   #1
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When is burning oil too much?

We have twin Nanni 135hp TDI 2002 engines that were marinized from Kubota base engine. After about 700hrs port engine doesnít burn much oil at all and no smoke even at start up. The starboard engine however does smoke at start up but not much underway. On a recent trip we went 16hrs and burned about 2 quarts of oil on the starboard engine. The engine tends to be harder to start too, probably indicating a compression problem. Power from the starboard engine seems about the same as the port side.

My question is how much oil burning is excessive? When do you decide to rebuild the engine?
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Old 11-05-2021, 10:25   #2
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Re: When is burning oil too much?

A quart in 8 hours is definitely excessive. But it may not require a rebuild to correct. It would be worth getting a mechanic that knows those engines well to go over it.



Are these turbocharged engines? If so, it's possible you have a bad turbo seal feeding oil into the engine.
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Old 11-05-2021, 10:41   #3
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Re: When is burning oil too much?

How much? two litres of oil in a day

That needs looking at because you just know it isn't going to get better.

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Old 11-05-2021, 10:53   #4
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Re: When is burning oil too much?

It is possible that you’re overfilling the oil sump, and the perceived “burning” of oil is just a result of that.
Many automotive or industrial motors that are marinised use an oil sump designed for primarily horizontal crankshaft orientation, and are then installed at an angle, and further complicated by the running angle of the boat.
You might find that if you let the oil level drop a bit, it may stabilize at a significantly lower level than the marks on the dipstick, without sacrificing any integrity.
Hard starting diesels most often are suffering fuel supply problems.
700 hours should be a drop in the bucket to the life of the engine, rebuilding seems like an unlikely necessity.
Find a GOOD mechanic to troubleshoot your motors!
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Old 11-05-2021, 18:41   #5
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Re: When is burning oil too much?

A compression test would give some answers. If in the past someone used too much ether, you could have broken rings. Rings are designed so the pressure of firing forces them against the cylinder, making a tight seal. Once they become broken, they're just along for the ride.
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Old 11-05-2021, 19:24   #6
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Re: When is burning oil too much?

Quote:
Originally Posted by Marcsailcat View Post
we went 16hrs and burned about 2 quarts of oil on the starboard engine[...]


My question is how much oil burning is excessive?

On a smaller diesel a quart in 25 hours is kind of a lot.


On the other hand it might go for another 1000 hours or more without getting any worse as long as you keep putting oil in it.



Quote:

When do you decide to rebuild the engine?

When and if it makes sense given your goals for the boat, the availability of time to do it or money to pay for it as the case may be, when the engine cannot be run any longer, when reliability becomes more critical than cost and the short-term downtime for the repair.


My advice would be to get an estimate on repairs. Though unlikely it may be something simple and easy to repair.
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Old 12-05-2021, 08:51   #7
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Re: When is burning oil too much?

For sailors with their smaller engines running hours at low revs ("motorsailing"), high oil consumption can be stopped by doing what the small print in the manual says: every four hours run a few minutes at maximum revs, cleaning the engine. It hurts, but tough love essential here.
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Old 12-05-2021, 09:26   #8
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Re: When is burning oil too much?

My westerbeke 42b burns about half a quart every 100 hours with rotella 15-40 t-4 oil. Last oil change I just decided to try full synthetic Rotella T6 Iíve burned a quart and a half to 2 quarts this hundred hours.. might be oil you used. Iíd like to find a 20-50 to try but no luck finding any.
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Old 12-05-2021, 09:39   #9
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Re: When is burning oil too much?

I'd check the turbo charger first. Some other sources could be bad valve guide, valve stem seal, broken rings, stick rings. 1qt/8 hours is too much.

Agree with Lepke that a compression test is a good idea.
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Old 12-05-2021, 12:06   #10
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Re: When is burning oil too much?

Quote:
Originally Posted by Marcsailcat View Post
We have twin Nanni 135hp TDI 2002 engines that were marinized from Kubota base engine. After about 700hrs port engine doesnít burn much oil at all and no smoke even at start up. The starboard engine however does smoke at start up but not much underway. On a recent trip we went 16hrs and burned about 2 quarts of oil on the starboard engine. The engine tends to be harder to start too, probably indicating a compression problem. Power from the starboard engine seems about the same as the port side.

My question is how much oil burning is excessive? When do you decide to rebuild the engine?
You may only have a bad ring or valve guide.. I'd see about it before having major problems.
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Old 12-05-2021, 14:47   #11
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Re: When is burning oil too much?

Do the simplest diagnostics first.
Take off the oil filler cap (carefully) while the engine is hot and idling to observe crankcase pressure. What grade of engine oil and what spec?
Have the valve clearances ever been adjusted since the last dealer service?
Airfilter problems should show on the filter service gauge.
And more obscurely, if one engine is working harder than the other, the oil consumption may be more .... and sometimes less by comparison.
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Old 12-05-2021, 15:09   #12
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Re: When is burning oil too much?

Diesels love oil like a sailor loves rum.
~Captain Ron
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Old 12-05-2021, 16:28   #13
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Re: When is burning oil too much?

To diagnose bad rings you need to do a compression test both wet and dry. A leak down test would also be helpful. At 700 hours I would be surprised if you have a ring issue. A bad turbo seal would account for your oil loss as would a loose or dropped valve guide.
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Old 13-05-2021, 06:39   #14
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Re: When is burning oil too much?

A sure sign of needing a rebuild would be if the amount of oil used increases. That is from my experience with a GM 12VN71.
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Old 13-05-2021, 06:55   #15
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Re: When is burning oil too much?

I agree with the consensus so far here... 2 quarts in 8 hours is HUGELY excessive. It means you are probably routinely running with an oil sump that is quite short on oil which will pretty quickly cause other problems.

This is VERY unusual for a Kubota with only 700 hours. That is barely broken in! It is most certainly NOT routine wear and tear. Something is broken. Before you think about a rebuild, be sure all the other issues have been chased down. Oil can leave an engine lots of different ways.
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