A leaky head gasket is bad news for several reasons: Besides causing the engine to lose coolant and overheat, antifreeze entering the cylinder can wash away the oil that protects the rings and pistons against wear. Antifreeze in the crankcase can also dilute and contaminate the oil, which may lead to bearing wear and failure too.
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All engines produce a small amount of visible steam in the exhaust when they are first started on a cold morning. If you see white smoke when the engine is running at normal temperature (and it is not below freezing outside), there could be coolant in the exhaust from a leaky head gasket. The exhaust may also have a sweet smell.