The weather is beginning to change here in NJ and as I pulled into traffic this morning in my 98 E430 (85k miles) I noticed a trail of vapor behind me. Dashboard said it was 62 F outside and it brought up the question that gnaws as me every winter.

Why in the world does my car put out so much vapor?

I wouldn't describe it as real smoke, although I have seen my car put out some sooty smoke in the past (and no, it is not a diesel) after sitting for a few days. But when cold my MB seem to generate more visible vapor than other cars I have had and other cars around me in traffic. And even when it is at normal operating temps it is putting out vapors into the cold air while other cars don't seem to be doing so.

I have my oil changed on a regular basis, neither my mechanic nor my onboard computer has ever said anything about the oil being low (which presumably would happen if I was buring oil). Call me sensitive or call me curious, but why does this happen?

 

If you dont smell antifreeze in the exhaust and the smoke does stop after the engine warms up ,then it's sounds like condensation in the exhaust burning off.The amount of condensation will depend on humidity as well.

 

Vapor is ok. Smoke is not.

 

Sounds like you are referring to the water vapor in the exhaust. The warmer the engine get's the hotter the exhaust the more will burn up before it exits the exhaust system.

 

I believe in an internal combustion engine for every litre of fuel burnt there is a litre of water vapour produced (steam) until the whole exhaust heats up you see it as water out the back

 

All excellent explanations, but what is it about the MB that causes it to emit vapor longer than other cars?

This morning I warmed up my wife's Disco and my E430 at the same time and then we left together. A mile later the Disco wasn't putting anything out while sitting at a stop light but I could see a faint trail behind my MB.

 

Bens engines have a higher compression ratio than most other cars=higher exhaust temp.