sick94

I searched but did not find the answer I was looking for. The car is a 1997 Pontiac Firebird, 3.8L, 82,000 miles. I replaced the water pump, installed a 180* thermostat (stock was 195*), and replaced the coolant on 10-30-2010 at 72,000 miles. Went through the winter without any problems and the heat worked great. Now that it's starting to get cold again, I turned on the heat and it worked perfectly fine.....the first day. The next day, I noticed that while the car was running and warmed up, the heat would only blow hot when the engine was revved up. In other words, at idle, the system would only blow cold air but as soon as I gave it throttle the heat instantly returned. Just a couple days ago, I noticed that the engine temperature gauge was really high for no reason. As soon as I revved up the engine the temperature went back down. I turned on the heater and to my surprise, it would blow only cold air no matter if the car was at idle or revved up. What's the deal? Do I have an air bubble in the system, stuck thermostat, clogged heater core, etc?

Z28Noob

Check the coolant level sounds like it is low and when you revved it up it would push through the heater core, hopefuly its just low and not that you either have a small leak good luck

rv93

id say your system is clogged somewhere. thats why at first, higher rpm (higher pressure from the water pump) would make it flow and give you heat.