We just had a used oil analysis performed on stargrrrl's Sunfire. Everything came back OK with the exception of 3% of the oil being fuel. My question is, what causes that. The lab says that short city driving trips can cause this as well as changing the oil right after it's been started and left to idle. She has complained about gas mileage lately. The car is mainly a commuter car, doing a 12 mile non highway round trip to work 5 days a week.

I would not be worried about 3% fuel. That is easily caused by blow-by& wash down, of which I would say that percentage is completely normal amount.

How long had the oil been in the car before this analysis was performed.....and why did you have it performed btw??

Oil had 4,000 on it. Mobil1 5w30. We did the test just to check the overall health of the engine. She'd like a new car and we wanted to see if we could wait a little or maybe we should speed the process up. Engine seems fine so we need to figure out how much longer her tranny is going to last. Here's the entire report:


JONATHAN: 3.0% of this sample was gas, which can come from lots of city driving or it can also be from taking the sample right after starting the engine and letting it idle. Since engine wear and oil viscosity both looked good we doubt your have a fuel injector problem. The universal averages show typical wear for the GM 2.4L 4-cylinder after 5,200 miles oil use. Your oil was in use for 4,000 miles and all wear metals read close to those averages. Silicon & insolubles were low showing good air and oil filtration. Try 5,000 miles next. Wear should still look good.



Unit Universal Ave.
Aluminum 3 4
Chromium 0 0
Iron 14 12
Copper 2 3
Lead 2 1
Tin 0 0
Molybdenum 70 60
Nickel 0 0
Manganese 1 1
Silver 0 0
Titanium 0 0
Potassium 1 1
Boron 45 87
Silicon 7 12
Sodium 5 13
Calcium 2236 1910
Magnesium 13 54
Phosphorus 624 617
Zinc 781 747
Barium 0 0


Acutal Should be
SUS Viscosity @210F 55.6 55-62
cSt Viscosity @ 100C 8.96 8.8-11.1
Flashpoint 305 >365
Fuel % 3.0 <2.0
Antifreze % 0 0
Water % 0 0
Insolubles 0.3 <0.6

Bah that didn't post right.

yeah, I see nothing to worry about at all.

John Benham wrote:That is easily caused by blow-by& wash down

I agree with that, I cant think of any where else oil and fuel are close enough for one to leak into the other. The injectors, fuel rail, and fuel lines are all external. A crack in a valve "cup" would cause it to burn oil or fuel.

I wouldn't worry about it.

You mentioned in your original post that she'd complained about the gas milage lately. What has it been and is it a dramatic change from the past?

She feels it's lower than it should be. She just got 19 MPG on her last tank. I realize that that number is affected by the winter temps right now. That's actually right inline with what the new EPA estimates for that year, engine, and trans. I guess in the past it's been a bit higher. On top of that, my car get's usually upwards of 25-28 MPG routinely. That sees much more prolonged highway than her car does.