Gasoline in Oil

An oil sample shows severe fuel dilution. The dealer didn’t do anything since he had no codes in system and the sensors were reading correct. Of course it was my fault for not changing the oil on time (over by 1200 miles - 100% synthetic oil)

Year and miles?
1200 miles over the change time is not a big deal, and is not the problem here.
I think that the main suspects would be leaky injector(s), leaking fuel pressure regulator, or some defect causing misfires.

Volvo XC-70 purchased at 22000 miles, used. My first change was at 26000, second at 34500 after long trip to west coast. The filter was changed about midway and oil topped off. The car starts easily and runs great, no misfires. Highway milage was just under 30 mpg with full vacation load.

I’m with Tardis on this. The overdue oil change is not the cause…unless perhaps the car has a long history of long overdue oil changes and that’s caused premature wearing out of the cylinders…

The only probable path from the fuel deivery system to the oil is past the rings, and severe dilution is a symptom of excess fuel being poured into the cylinders. Or a cylinder (or the cylinders) not firing reliably, often leaving the fuel in the cylinders in a fluid state. I agree with Tardis’ suggestions.

Do you drive short distances w/o the engine getting fully warmed up? Do you live in a cold area? It can be a problem in the winter, especially. That causes the blowby accumulation of fuel in the oil not to be evaporated when the oil warms up. Friend was able to light his ‘oil’ with a match, it was so bad! Are there any drivability symptoms?

Car milage a mix of highway and local. Car runs great. Current milage 37300. If the problem is grit in the injector it should run like it has grit in the injector but it doesn’t…thus no computer codes to lead the dealer’s mechanic. The dealer wouldn’t do a bottle test on the individual injectors…they just replace them but wouldn’t without a computer code.

Runs great, no misfires, no codes, 30 mpg loaded…I can understand why they’d be reluctant to spend time & money.

The two things I’d ahoot for is a compression check and a check of the fuel pressure regulator. If you have any mechanical aptitude you can do these yourself at low cost. The instructions will be with the gage. You may also want to see how the plugs look. A wet plug could be a clue.

I’m sort of surprised it runs so well with the oil being diluted by fuel. The two seem inconsistant.

How did the establish there was “severe fuel dilution”?

Oil Analyzers, Inc. tested the sample taken at the last change. Test kit purchased from Amsoil. I’m doing another test with the same folks for “false positive” but have to take the first report at face value until I get that result. Oil changed when weather still kinda warm and fall-like. No cold weather here until I changed the oil.

OK, good info, that leads me to the others’ ideas about a defective injector, regulator, etc. letting gas by the rings after shutdown. But being used, I’d also suggest TSM’s compression test, who knows if a piston’s rings or cylinder is bad…

Here’s the questions no one has asked just yet:

How long do you let the car idle for after you first start it up before you start driving?

How much time does your car spend idling in stop and go traffic on your way to work in the morning?

And what was the percentage of fuel dilution?
Trace? .2%? .5%? 1%? greater than 2%?

And what oil was it? Mobil 1 is not very good at dealing with higher levels of fuel dilution in comparison to other synthetic oils, like Castrol Syntec.


Unless all your driving was freeway in a mild climate, I would say you did not change oil often enough! When you changed the filter why did you not change the oil as well?

Short trip driving in an engine that has not had frequent oil changes usually results in gasoline and water working its way past the rings and into the oil. If you have leaking injectors it would guarantee gas in the oil.

Do you have any history as to how often the previous owner changed oil?

It’s time to have a compression test done on the engine to determine what is getting past the rings. If you’re lucky it’s the injectors leaking.

Please let us know what the test shows.

P.S. What viscosity synthetic oil were you using?