I started My 2005 Pontiac grand am 3.4 had a bunch of light grey smoke come out the exhaust I drove it about a mile down the road an it over heated.now its running fine what could cause this

Thermostat may have hung up should be changed? When was the last time it done. Flush the system with a good system flush, New thermostat and new coolent with 50% water, 50% coolent.

I changed it back in October but I haven't did a system flush. But would that cause it to randomly blow light grey out the exhaust smoke after sitting all night.

The grey or blue grey smoke, is an indication of oul being burned. White smoke is antifreeze/water

Um going to take my thermostat out return it an do a flush today

Good luck

The morning smoke is due to valve seals/guides leaking by and collecting on top of the piston. So when u start it up in the morning its burns off the excess oil.