no heat when driving

hello i have a 1990 olds calais and it runs great i get a little heat when the car is at idle in park then when i put in drive and get going there is
no heat. does anyone know what is going on here. thank you

put a peice of carboard in front (towards headlites not cooling fan) of your radiator.

Make sure there is enough coolant.

10 to 1 says that your thermostat has failed open and your water pump is contantly moving the water from your block through your radiator. If the water in your block doesn't have enough time to warm up, you will not get any heat. I'd say check your thermostat.

i had a 94 cutlass do the same, i was told the thermastat was stuck open, sold it before i fixed it though

Thought about that too but its getting heat while idling though?

trust me, I bet its your thermostat. My wife's sunbird was doing the same thing, does your temp needle even move at all? I spent 6 bucks for the new part, and now she has her heater back, and especially her defroster, and the needle moves as well.

put a peice of carboard in front (towards headlites not cooling fan) of your radiator.

"djnoname" is correct about using the cardboard to diagnose the problem. If blocking the air through the radiator corrects the problem then it 100% sure it's the thermostat. Just make sure you don't block all the air as the car will overheat.