Diesel content in oil

[bill424]

I am trying to buy a boat with a ~2010 Yanmar diesel. The surveyor's report included oil analysis which shows ~15% diesel in it, which seems bad.

The yard has started taking it apart for diagnosis and don't see anything wrong and think that an oil change is all that is required. Given all the awful things that I was considering as possibilities, I'm relieved but apprehensive.

The boat has been on the hard for two years in NY. Is it plausible that diesel in the fuel lines (or tank) made their way into the engine and thence into the oil?

Any other theories?

Thanks

[fregata]

I would look at it this way:

There is diesel in the oil and the mechanics are stumped as to why. I’d be thankful that’s not my boat because it sounds like an expensive problem to troubleshoot.

[barnab]

It sounds like you didn't buy the boat yet - either negotiate the price to be reduced for a new engine or walk away

[Statistical]

That is a crazy amount of diesel to have in the oil. Even trace amounts like >0.1% is something to be concerned about.

I agree with others this would be a walk away type situation because there is no common explanation for that much diesel in the oil. If one or more rings were bad you can get diesel forced into the oil during compression but not 15%.

Depending on the engine size that is anywhere from a half quart to a full quart of diesel mixed into the oil.

[Bellinghamster]

Diesel dilution in oil isn't uncommon, which is why it's usually part of a "standard" oil analysis. Anything above 4% fuel dilution is considered abnormal and the cause should be found and remedied. 15% is a lot, but that means the cause should be easier to find . If the compression test and oil analysis otherwise came back OK, I woudn't consider it a deal breaker, but does need to be addressed.

Typical paths for diesel to get into the oil are:
Leaking lift pump seals or diaphragm
Leaking injection pump seal(s)
Leaking injector high pressure line connection (engines that have the injectors are under the valve cover)
Malfunctioning fuel injector
and to a lesser extent, worn piston rings.

Worn rings should be evident with a compression test
Injector testing in common, not too expensive and injectors are easily replaceable
Leaking injection lines should be evident to a competent mechanic
Lift pumps are fairly inexpensive and easy to replace it if suspect
Injection pump can be removed and bench tested for leaks, re-sealed if/when necessary.

[Cheechako]

Bellinghamster's list is good.

Stuck valves could do it as the high pressure blows fuel past the rings into the crankcase.
What Yanmar model is it?
Is it a Turbo?
Some Yanmars have a oil passage which is susceptible to a leaky head gasket, maybe fuel could get in the oil via that?
Some models have had piston issues.

[bill424]

It's a 4JH5E, no turbo.

The thing I should have mentioned is that in spite of its age, it hasn't been used much; estimated at 100hrs or so.

Estimated because it has that lovely Yanmar panel that reports hours on an LCD display. As is normal for that panel after a few years, it probably knows the hour number, but can't display it.

I'll fix it if I buy the boat & put a mechanical counter in there too.

[dannc]

The used oil reports I get from Blackstone Labs says that the oil should have less than .5% fuel. I have had diesel in the engine oil due to extensive idling in the truck and slightly low RPMs, say 1500-1600, in my tractor's Yanmar engine. Once I stopped having to travel a certain route that had lots of traffic in my truck, there was no more fuel in the oil. I increased the RPM on the tractor to 1800 and no more fuel in the oil. In both engines, the amount of fuel in the engine oil was less than .5%. 15% is quite a bit of fuel in the oil...

[Tupaia]

Is the fuel tank above the engine? Left with taps open and a failed lift pump seal/gasket will constantly top up the oil with diesel.

[grantmc]

Walk away quickly, walk away!

[Marathon1150]

Originally Posted by Bellinghamster

Diesel dilution in oil isn't uncommon, which is why it's usually part of a "standard" oil analysis. Anything above 4% fuel dilution is considered abnormal and the cause should be found and remedied. 15% is a lot, but that means the cause should be easier to find . If the compression test and oil analysis otherwise came back OK, I woudn't consider it a deal breaker, but does need to be addressed.

Typical paths for diesel to get into the oil are:
Leaking lift pump seals or diaphragm
Leaking injection pump seal(s)
Leaking injector high pressure line connection (engines that have the injectors are under the valve cover)
Malfunctioning fuel injector
and to a lesser extent, worn piston rings.

Worn rings should be evident with a compression test
Injector testing in common, not too expensive and injectors are easily replaceable
Leaking injection lines should be evident to a competent mechanic
Lift pumps are fairly inexpensive and easy to replace it if suspect
Injection pump can be removed and bench tested for leaks, re-sealed if/when necessary.

We are going through the process of identifying the source of diesel in the oil of the Perkins 4.108 in our boat. So far we have:
1. removed and resealed the injector pump - $$$
2. Removed and replaced the mechanical lift pump with an electric pump - $$$
3. The injectors are in the shop as I write and the injector shop believes that this is the source of the problem. Reinstallation will take place next week and I will know if this was the problem and I will know the cost.

One item not in the above list is the cold start device. Other web sources have indicated that this is potential cause. If the injector rebuild doesn't work, that will be the next item to be examined and likely blocked off because we have never used it.

Our experience suggests that you be wary regarding the diesel in the oil problem. It can be a very difficult and costly problem to diagnose and repair.

Good luck.

[skipperpete]

Originally Posted by bill424

It's a 4JH5E, no turbo.

The thing I should have mentioned is that in spite of its age, it hasn't been used much; estimated at 100hrs or so.

Estimated because it has that lovely Yanmar panel that reports hours on an LCD display. As is normal for that panel after a few years, it probably knows the hour number, but can't display it.

I'll fix it if I buy the boat & put a mechanical counter in there too.

I can understand why the mechanic is a bit perplexed, that engine ( usually) lacks a mechanical lift pump and uses an electric feed pump… plus the MP2 injector pump isn’t prone to leaking fuel into the crankcase, but it seems to be the only candidate, the injectors are external so unlikely to be them either. Change the oil and do another oil sample at the next change.

[Island Time O25]

Pardon my naivete but what is the worst case scenario of diesel in the oil? i.e. the engine will die today/tomorrow, in 1 month, in a year or what?

[bill424]

My understanding is that it interferes with the proper lubrication of the engine and can let bearings get hot enough to damage/destroy them, which can lead to catastrophic failure.

As to timetable, I don't know, but my surveyor felt it was a disaster waiting to happen.

[skipperpete]

Originally Posted by Marathon1150

We are going through the process of identifying the source of diesel in the oil of the Perkins 4.108 in our boat. So far we have:
1. removed and resealed the injector pump - $$$
2. Removed and replaced the mechanical lift pump with an electric pump - $$$
3. The injectors are in the shop as I write and the injector shop believes that this is the source of the problem. Reinstallation will take place next week and I will know if this was the problem and I will know the cost.

One item not in the above list is the cold start device. Other web sources have indicated that this is potential cause. If the injector rebuild doesn't work, that will be the next item to be examined and likely blocked off because we have never used it.

Our experience suggests that you be wary regarding the diesel in the oil problem. It can be a very difficult and costly problem to diagnose and repair.

Good luck.

The injector pump on the Perkins 4-108 can and will leak into the crankcase if the return line is blocked or returning to an elevated point on the fuel tank although more commonly on day tanks than on engine level tanks, the shaft seals on the DPA pump are very fragile and unlike most lip seals , these ones are secure on the driveshaft and spin in the housing.
The coldstart is definitely a possibility but usually has other symptoms like …. A lot of smoke at startup and sometimes at idle. The coldstart is adjustable and relies on the ball being held onto its seat by the adjusting screw or it will leak.