headgasket ?

how would i know when its gone?? i took the car to 3 diferent shops and every single 1 tells me different crap the thermostat, the head gasket and so on but the last place told me it was this. he said that u could smell the combustion fumes when u open the cap on the radiator but thats it. i c no water in my oil or anything i just want to know for sure b4 i take it in for this prob thanks

I think compression test will give the answer.

Sam