Sample temperature

[Sonataman]

Is it better to take a hot sample, why?

What differences would you see in a used oil analysis if you took a sample with the oil fully up to temp, then a sample after the oil was at ambient? Would there be a fuel difference?

The reason I ask is I am getting 3% of fuel dilution on a vehicle which never sees short trips. Each use is at least 50 miles and the oil does not smell like fuel.

 

[Donald]

A cold sample might show water from condensation which is not really a problem.

For fuel dilution, is it a DI engine? Have you checked the compression?

Has this issue been seen on two used oil analysis? Always could be an error at the lab if only seen on one.

 

[Corvette Owner]

I would be more concerned about settling of oil when cold. I think the "mixing" of oil by running engine would give a better sample. Does fuel settle to the bottom?

Gasoline should float on the top of oil.

 

[Donald]

I was thinking the OP was talking about warmed up a bit and hot. Obviously cold is not good due to settling as the prior poster mentions.

 

[dparm]

The thinking behind taking a sample when the oil is "hot" is this:

1. You've had sufficient time to burn off or filter out any contaminants that may have temporarily accumulated since last driving
2. The oil will drain/pump out better as it will have thinned out
3. The oil will have circulated sufficiently to ensure you don't get a disproportionate amount of sludge or heavier contaminants that settled to the bottom of the pan


If you're consistently getting fuel dilution, you may want to check if there is a mechanical problem such as a leaking or faulty injector, or perhaps a flaky oxygen sensor that is causing the motor to over-richen the mixture.

 

[Sonataman]

Originally Posted By: Donald
A cold sample might show water from condensation which is not really a problem.

For fuel dilution, is it a DI engine? Have you checked the compression?

Has this issue been seen on two used oil analysis? Always could be an error at the lab if only seen on one.


Carb'd motorcycle engine, compression is good. Seen on two used oil analysis, one at 2.8% and this last one at 3.4%. After the first one I suspected a float seat but wanted to be sure something was amiss so waited for this uoa. Pulling the carbs apart tomorrow to find out.