"Blowing up" is usually used to describe a severe and expensive failure. It will not actually explode.

If the head gasket is leaking coolant into the cylinder you have a problem. Cranking the engine with one cylinder full of coolant can "hydrolock" the engine, usually resulting in a broken piston or bent connecting rod. You will have just "blown up" the engine.

There are many other types of headgasket failures (recently classified by Stevebfl, I think) that may take a while to become serious. Try a search and you'll find a lot of info.

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D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.