over heating 1988 gmc v1500 suburban 4wd 8cyl k 5.7L?

[kiki]

it started over heating all of a sudden and pushed steam out the defrost vent when the heater was off what could this be?

 

[Molson02536]

it started over heating all of a sudden and pushed steam out the defrost vent when the heater was off what could this be?

Could be a stuck thermostat in the close position and your heater core has a leak in it and will need to be replaced. Before taking your heater core out, inspect the heater core hoses and clamps. If your luck, it's just a bad clamp and if your not. Then your going to have to replace the Heater core and don't forget to replace your thermostat.

Good luck and keep us posted.