White smoke when i start up my car but doesnt keep blowing smoke.?

I have a 1989 camaro IROC Z28 and when I start it up after I let it sit a day it shoots white smoke but when I drive the thermo says it isn't overheating or even that its hot and it doesn't shoot smoke when I'm driving or if the car is warmed up and I start it again. I know my first response was head gasket but as I sayed no overheating or any other engine probs.