35d Engine Oil Dilution by Fuel?

[Rich807]

Anyone seen diesel getting into the crankcase on these motors? I've done a couple of searches on the forum but nothing is popping up for me.

ETA: I've seen an issue where 2x now in as many years where I believe my oil level has risen after prolonged higher speed highway driving (at least as best as I can tell).

Did oil analysis after last episode of high oil level appeared & the O/A confirmed fuel dilution. Nothing that degraded the viscosity enough to compromise the engine (according to the lab), but definitely enough to validate why the capacity had risen to an extra half to 1-quart of fluid in the crankcase.

I don't let the car idle much, especially on cold starts. Wondering if I may have an injector issue or perhaps something within the DPF regen system that's dumping extra fuel at higher sustained speeds & it's ended up in the crankcase?

[Thecastle]

Fuel dilution is an issue in all engines. IT's a question of how bad.

How long does it take for your engine to raise the oil level? Intriguingly, my diesel burned about 1 qt every 5-7K miles. How many miles on your car?

Diesel fuel dilution of the engine oil occurs due to internal leakage of the fuel injection system. Causes vary, but can be related to sealing ring failure, loose connections, faulty fuel injectors, or even the result of extended periods of idling.

Not enough info to say the cause of your issue. But I'd take it to a diesel mechanic and get those injectors checked. One is probably leaking. Low fuel rail pressure would generally throw an SES light.

I'd also check the operating temp of the engine, to see if you have a bad thermostat. Which means your engine never gets to operating temp, runs the glow plugs all the time which eventually burn out then you won't get proper combustion especially at cold start.

My powerjoke when it had bad glow plugs/module. If you could get it started blew huge clouds of white smoke due to incomplete combustion it also has no dpf. The 335D has a much higher pressure fuel system so the fuel better atomizes and combusts without glow plugs. Which is nice not waiting 30 seconds for that glow plug light to go off.

[Rich807]

Far as I can tell the fuel dilution in the oil isn't happening at all as long as I don't take the car out on sustained highway driving trips. For instance, my normal around the city driving involves mostly what I'd consider faster than normal / typical city street speeds (people driving 45-60mph) to running the freeways around the outskirts of the city. This type of driving *might* be up above 65mph as a norm, but hardly ever for more than 15-20 min stints.

My car has 141k mi on it.

This is like my 4th diesel vehicle I've owned over the years & I've been driving company/Gov't diesels routinely for 30+ years. I'm not stranger to them by any means, but the DEF-based emissions ones are kind of a mystery to me.

No CEL lights, no codes thrown. When it's happened I've ended up with a quart of diesel (or thereabouts) in the crank case.... kind of all at once or nearly all at once.

I also had a non-DPF powerstroke (owned it for 10 years), so I know about cold running characteristics of some of those (sounded like a busted ass washing machine until it warmed up).

I haven't checked the operating temp of the engine temp yet. Will have to try & do that if my Foxwell has that ability. The thing that's got me scratching my head is I'd think if it was a cold start/cold condition thing I would expect to get building levels of fuel dilution over time in my daily driving cycle, but I'm not getting that.

[Rich807]

Originally Posted by Thecastle

I'd also check the operating temp of the engine

Just checked it after driving around town a bit: 74C/165F