97 gmc safari mini van, heating problems?

[scorpio6969]

when the van is fully warmed up and temp gauge shows it is warmed , at idle heat blowing out of vents is luke warm, but if u raise idle or drive it gets really nice and hot and temp gauge stays the same as when it was idleing and luke warm air ? any ideas? thermostat should regulate heat once warmed up whether at idle or driving ?
when increasing the idle , even just a little , why would heat get hotter even though motor isnt ?
aaron, the heat should be constant , the thermostat regulates it whether driving or idling
i think i just answered my own question, must be thermostat?
not low on coolant, just changed coolant

 

[Aaron M]

At idle the rate of warm anti-freeze going through the under dash radiator is slower than if it is reved because only so much heat can be pulled from so much liquid.