For several months (3 - 4), my exhaust has been very thick after a cold start. This continues for about 10 - 15 minutes until the engine warms up, and then everything is okay. During this time, the car passed the Illinois emissions test without any problem (I actually thought it might fail). I can smell gas in the exhaust, and some might say that the emission is not completely white, but a little bluish white.

I was concerned that I had a head-gasket problem, but carefully monitoring coolant levels indicated they were not changing dramatically. Maybe I've lost 20 ml to 30 ml in the reservoir since my last coolant change (October '01). The engine oil is not frothy/milky, which also argues against head-gasket failure.

But the thick exhaust has been bugging me. So I got the coolant tested for CO, and it came up clean. They guy that did the testing suggested that I try a different brand of gasoline.

I have been using 93-Octane brand "C", and my tank needed a fill, so I switched yesterday to 93-Octane of another brand yesterday. I've had 3 cold-starts since then, and the volume of the thick steamy exhaust has diminished considerably, and it goes away completely in 5 minutes. So, the good news is that it probably was steam, and not burning oil or coolant.

I have never believed that different brands of gas make any difference -- always choosing the cheapest 93 octane I can find. Probably a coincidence -- but noteworthy anyway. Has anyone else noticed brand of gasoline making a difference in performance or any other measurable parameter?

Curious,
Ashok