Gasoline in a Crankcase

[Danh]

Two things seem pretty clear to me:

1) Gasoline is less dense than motor oil
2) If left in open containers, gasoline will evaporate fairly quickly, motor oil will not

If these things are true, when fuel dilution occurs and the engine is off for a period of time, why doesn’t gasoline separate from engine oil, float to the surface of the sump and evaporate, reducing fuel dilution? Does the gasoline/oil combination result in a homogenized mixture so no separation occurs? Does the closed sump prevent gasoline vapors from escaping?

It would be nice to think that a sump full of fuel diluted engine oil would heal itself with time, but it doesn’t seem to work that way. Thoughts?

 

[OVERKILL]

Two things seem pretty clear to me:

1) Gasoline is less dense than motor oil
2) If left in open containers, gasoline will evaporate fairly quickly, motor oil will not

If these things are true, when fuel dilution occurs and the engine is off for a period of time, why doesn’t gasoline separate from engine oil, float to the surface of the sump and evaporate, reducing fuel dilution? Does the gasoline/oil combination result in a homogenized mixture so no separation occurs? Does the closed sump prevent gasoline vapors from escaping?

It would be nice to think that a sump full of fuel diluted engine oil would heal itself with time, but it doesn’t seem to work that way. Thoughts?

Gasoline is a hydrocarbon, engine oil is a hydrocarbon, they mix. So the light fractions aren't sitting on top of the oil ready to evaporate.

 

[JohnnyG]

Think of a two stroke engine. No separation in the gas/oil mixture.
Fuel dilution doesn't normally happen when an engine is not running, unless there's a leaking injector or some other issue.
The biggest problems seem to occur when a car prone to dilution, is not operated at a high enough temperature, for a long enough period of time. Think short trips and cool weather.

 

[BMWTurboDzl]

Two things seem pretty clear to me:

1) Gasoline is less dense than motor oil
2) If left in open containers, gasoline will evaporate fairly quickly, motor oil will not

If these things are true, when fuel dilution occurs and the engine is off for a period of time, why doesn’t gasoline separate from engine oil, float to the surface of the sump and evaporate, reducing fuel dilution? Does the gasoline/oil combination result in a homogenized mixture so no separation occurs? Does the closed sump prevent gasoline vapors from escaping?

It would be nice to think that a sump full of fuel diluted engine oil would heal itself with time, but it doesn’t seem to work that way. Thoughts?

Naw. Gasoline mix in the sump and it's essentially a closed system when not running.

 

[tasch72]

 

[benjy]

its well noted fuel in the oil can be quite common with modern direct injected engines + even a port injected like my aunts 99 cherokee has issues from short trips, not gas but WATER!!