Question about fuel dilution in oil

[SLCraig]

This is a topic I don't know much about.

I have recently had what MAY be a cause for concern with my current fill of oil, which is coming up due to be drained anyways, but riddle me this..

Is it a problem that a few days ago my car was operating on 3cyl, dumping gas (assuming the injector was still running on that cyl) into the cylinder during a period of about 15-20km (10-12 miles) where I had to limp it home?

The problem was a bad coil, which was fixed right away and its working fine now.

But, should I drain the oil out early because of this? It was probably a good 30 minutes of running on 3 cylinders, the whole time dumping unburnt gas into my #1 cylinder.

Thoughts?

 

[HTSS_TR]

You should at least smell the oil dipstick, if it has any gasoline smell than dump the oil.

 

[PT1]

Change the oil.

 

[SLCraig]

Originally Posted By: PT1
Change the oil.


Even if it were just the beginning of an OCI?
I just want to understand if this is a potentially harmful (to the oil) thing to have happen.

 

[JAG]

The biggest risk is huge viscosity loss. Over time as the fuel evaporates from the oil the viscosity will rise again. Then there is the matter of the permanent chemical effects that significant fuel dilution causes. The onset of engine deposits will happen at an earlier OCI than it otherwise would have.

 

[SLCraig]

Originally Posted By: JAG
The biggest risk is huge viscosity loss. Over time as the fuel evaporates from the oil the viscosity will rise again. Then there is the matter of the permanent chemical effects that significant fuel dilution causes. The onset of engine deposits will happen at an earlier OCI than it otherwise would have.


Alright, that is fair and makes sense. Since I'm due for an oil change probably now or within 500mi anyways, I will just go ahead and dump it tomorrow.

 

[Pablo]

It does make sense, but also having fuel in your oil causes an acceleration in oxidation of your oil leading to ring deposits and other nasty effects.

 

[440Magnum]

I'm going to go a little bit against the grain here.

If this happened with the engine and oil fully up to temperature, then I don't think you have much (if any) fuel contamination. The fuel would never even go into solution in the oil with the engine metal and the oil itself fully heated up- most of it would go out the tailpipe (you might have a well-overcooked catalyst) and what did go past the rings would have gotten pulled right back out by the PCV system.

Fuel dilution happens primarily during COLD engine operation when the engine is running at an enriched A/F ratio and the oil is too cold to keep even the much more volatile gasoline from condensing. If you drove the car this way for several days, including when cold, then you'd have a ton of fuel dilution.

Since you're near an oil change anyway, go ahead and do it for good measure. If this had been right at the start of an OCI, I'd have just taken it for a long highway run at gentle throttle after fixing the coil to get the oil good and hot to evaporate out the dissolved gasoline.

 

[SLCraig]

Thanks a lot for your insight Magnum, that also does make sense when broken down.. And yes, the car was at operating temp. Luckily I had restarted the car after only 15-20 mins of not running and that is when the problem occured (but not close to home) so the drive home was basically at full temp 90% of the way.

Also, just cleaned my PCV valve and hose so was crystal clear for the evaporation to occur.

Going to do an oil change anyways, have some PP 5W30 to go in

 

[benjamming]

440,

Not everything is burnt when high levels of fuel dilution are present. It will irreversibly damage the oil.

 

[Eddie]

Take the vehicle out for a long drive like 15 miles to heat up the oil and forget it.

 

[mechtech2]

Most of the gas [if any] was blown out the exhaust.
If your oil level did not go up, and does not smell, you have no immediate problems. Normal driving will pretty much fix a small amount of fuel in the oil.
Maybe shorten your next OCI.

 

[SLCraig]

Originally Posted By: Eddie
Take the vehicle out for a long drive like 15 miles to heat up the oil and forget it.


I have to drive 90 miles a day to work secondary highway (60-70mph) every day, so thats not a problem.