is you engine light on? Is it throwin any misfire codes, & is there white smoke from your exhaust? Check your engine's oil, is it thinned out or milky? AND, does the car have trouble cranking? If so, then its most likely the headgasket.

Grab a really good flashlight, open up all sparkplugs, and shine light down the each cylinder & check if theres moisture or leaking coolant in there.