WRAL WeatherCenter Blog

I dont know why every morning when it is cold (20*-40*) outside i see white smoke comming out of my car muffler why is it?

Posted February 3, 2007

MIKE MOSS SAYS:      Mike,    One of the components of automobile exhaust is water vapor, and when the temperature of the tailpipe is still cool enough to reduce the temperature of the exhaust to the dew point of that exhaust, the vapor condenses out into tiny droplets. In some cases, the water may remain in vapor form (invisible) until it leaves the tailpipe and mixes with cool ambient air. If the resulting mixture has a dew point equal to or greater than the temperature, again droplets will form and you will see the "white smoke." This is not smoke, of course, it is the same sort of condensate that becomes visible when you exhale on a cold morning and can "see your breath."

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