No not necessarily, thermostat only opens once coolant reaches certain temp. Normally around 185F.
A failed head gasket will normally cause engine to idle slightly rough and you may also find coolant mixed into the engine oil. Easy way to check for cracked head gasket is to remove radiator cap WHEN COLD, then start motor and if coolant shoots up out of radiator cap opening then most likely head gasket is bad.
Wednesday, May 19th, 2010 AT 7:06 PM