Diesel content in oil

[Shaneesprit]

Originally Posted by 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

Change the oil and insist on a sea trail - 1 hour at near full throttle, this not only gives you confidence, it’s also most likely the cure.
Diesel in the fuel is either caused by a leaking mechanical lift pump -if it has one have it replaced with a genuine Yanmar pump or have it removed and an Electric version fitted - again buy quality (pay for this yourself if you have to I would not make a small pump a deal breaker)
The other cause is simply engines that have been used to charge batteries while at anchor, doing this means the internal engine temperature does not get up to temperature and the piston rings don’t seal and they sweep fuel into the sump, the good news is the best thing for this is a sea trail - 1 hour at near full throttle, which is exactly what you need to have confidence in the engine.

[Cheechako]

Here's an oddball thing that caused getting diesel in the oil for me: A rocker arm pushrod had popped off the rocker arm. The 4 cylinder Perkins 4-236 ran fine. We didn't even realize it was running on 3 cylinders!
We tried all the usual things, lift pump, injectors rebuilt etc.
After a lot of messing around, finally we popped off the valve cover and there was the pushrod, sitting off to the side of the rocker arm! So one valve never opened and thus forced fuel into the crankcase past the rings when the piston would come up! We ran the boat for a couple days before finding the fuel in the crank case.

[Dockhead]

Originally Posted by 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?

It could mean that the engine needs a complete overhaul because the rings and bores are shot -- $$$.


If it's been run with that much diesel in the oil for a long time, it could have ruined bearings, again -- complete overhaul -- $$$.


I wouldn't necessarily walk away just yet, but you will need a really thorough engine survey to determine whether it's damaged -- leak down test, oil pressure, etc. Besides finding and correcting the source.

[Dockhead]

Originally Posted by NYSail

Failed fuel lift pump diaphragm would be the first place I would look. Easy to check for a mechanic….

Not on a 4JH Yanmar. The fuel pump is at the end of the injection pump and doesn't have a diaphragm.

[Scubaseas]

What SkipperPete said. There is an electric lift pump on the 4JH5E. I have on in my boat. I would say most likely cause would be seal on injection pump. Not cheap but not deal killer IMHO.

Change the oil, Run it a while and then retest after maybe 20 hours? Keep an eye on the oil level checking after it's shut down and at the same temp. Like before starting each morning. If there is no rise in the level worry less. If it rises noticeable in the first hour or three and smells like diesel take the injection pump out for repair.

[dannc]

Take an oil sample and send it to a lab like Blackstone oil labs. The sample should show if there are other problems besides the fuel in the oil.

[Mickeyrouse]

If that engine is out, no point in it going back in without rings, valve job, bearings, gaskets, and seals. That would be a mere fraction of a new engine and would extended its useful life many years. And you know for sure everything will fit and line up properly, not so with some other kind of engine. And that diesel in the oil will disappear.

[Bloodhound]

Originally Posted by dannc

Take an oil sample and send it to a lab like Blackstone oil labs. The sample should show if there are other problems besides the fuel in the oil.

Before getting too excited about this, I'd have the oil re-analyzed. 15% fuel in engine oil is absurd and analysis errors (and reporting errors) have been made before.

[Icarus]

Leaky injector pump or lift pump?

[Icarus]

It's not about 'walking away'..It's about finding the issue..

[lifeofreilly57]

Not sure on that particular motor but quite often a leaking fuel pump with a failing diaghram can put diesel in the crankcase like your seeing, i've experienced this in the past.
Otherwise it gets more expensive, glazed or worn cylinders, injector pump/fuel system issues, and the list goes on.
Unfortunately my diesel was badly overheated by a transport crew and caused the #4 piston ring lands to disintegrate blowing the ings into the crankcase. Fortunately I've rebuilt a number of gas and diesel engines, so I was able to fix it affordably, unless your capable of doing that you should either negotiate a price allowing the engine to be replaced/repaired or walk away.
My other concern is if the engine was badly maintained, how well was the rest of the boat maintained? Rig, systems, electrical?

[lifeofreilly57]

Originally Posted by Bloodhound

Before getting too excited about this, I'd have the oil re-analyzed. 15% fuel in engine oil is absurd and analysis errors (and reporting errors) have been made before.

When the fuel pump started failing on one motor I noticed it on my daily dipstick check, it put abou 3 quarts of diesel into the oil pan. still ran fine and only showed a slight change in oil pressure, so 15% isn't that absurd.
That motor wasn't damaged by the diesel in the oil but the issue was found right away. Its still running fine 15 years later with the current owner.

[Statistical]

Originally Posted by lifeofreilly57

Not sure on that particular motor but quite often a leaking fuel pump with a failing diaghram can put diesel in the crankcase like your seeing, i've experienced this in the past.
Otherwise it gets more expensive, glazed or worn cylinders, injector pump/fuel system issues, and the list goes on.
Unfortunately my diesel was badly overheated by a transport crew and caused the #4 piston ring lands to disintegrate blowing the ings into the crankcase. Fortunately I've rebuilt a number of gas and diesel engines, so I was able to fix it affordably, unless your capable of doing that you should either negotiate a price allowing the engine to be replaced/repaired or walk away.
My other concern is if the engine was badly maintained, how well was the rest of the boat maintained? Rig, systems, electrical?

The other issue is how long was the engine run with diesel diluted oil. Maybe the leak happened after the last usage maybe it was only a few hours maybe it was hundreds of hours without sufficient lubrication.

Even if you find the source of the diesel intrusion, fix it, drain and clean the crankcase, and refill it with new oil what unknown excess wear happened when the engine was run without proper lubrication?

[lifeofreilly57]

One other thing I forgot to say, get a compression test before going too far with troubleshooting, it can often prevent a lot of unnecessary work being billed. Yards love billable hours. Compression check, check fuel pump for leaking, check high pressure distribution pump for leaks into the crankcase, then and only then, go further into the engine.

[lifeofreilly57]

Originally Posted by Statistical

The other issue is how long was the engine run with diesel diluted oil. Maybe the leak happened after the last usage maybe it was only a few hours maybe it was hundreds of hours without sufficient lubrication.

Even if you find the source of the diesel intrusion, fix it, drain and clean the crankcase, and refill it with new oil what unknown excess wear happened when the engine was run without proper lubrication?

True, thats why I have an oil filter cutter, and several magnets, in a situation like that I'd pull the existing oil filter, cut it open and inspect it under my lighted shop magnifying glass, also run a magnet through the oil that was drained.
In this case the oil analysis that found the diesel should have picked up any metal that was present. Of course it depends on what they paid for and who did the testing.
Diesel does have some lubricating properties but not the film strength properties of oil, this would effect the crank bearings more than the cylinders, a decent oil evaluation would be able to discern between ring/piston metallergy and bearing material, which if the crank is still in spec would only require a journal polish and new bearings.
The bearings are softer than the journals, I've pulled cranks where the bearings had small amounts of metal embedded in the bearing material but no damage to the crank journals, in those cases the journals got polished and new bearings installed.
Always interesting getting in those cans of worms.