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I have a 2003 Monte Carlo SS 3.8 engine not super charged.
Problem one: Changed the thermostat because I wasn't getting heat in the car and thought it was sticking open. Now, at idle it will go up to normal temperature idling in the driveway. If I drive down the road the temperature gauge drops about 25 degrees and stays there. The thermostat is a 195 degree thermostat but it runs well below that, by about 25 degrees, driving down the road.

Problem two. When the car is at normal temperature sitting idling, if I turn my heater fan on, the air is warm about a minute at most and cools down to about 45 degrees. The temperature control lever works. If I turn the heat down, the air gets colder. If I set it all the way up, I get 45 degree air. The only time I have any heat is by letting it idle to running temp and then it lasts about one minute. Driving down the road when the temperature gauge is down 25 degrees, there is no heat.

Any help greatly appreciated....


   
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no heat from the heater is usually a sign of low coolant. you get air stuck in the heater core, so no heat.

engine running too cold is usually a poor thermostat. and you get a code P0128 for too cold too long.

is this thermostat doing the same thing as the old thermostat?

This is where a thermal imager would come in handy.


   
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carriedi wrote:
> no heat from the heater is usually a sign of low coolant. you get air
> stuck in the heater core, so no heat.
>
> engine running too cold is usually a poor thermostat. and you get a code
> P0128 for too cold too long.
>
> is this thermostat doing the same thing as the old thermostat?
>
> This is where a thermal imager would come in handy.

Top heater hose is cool to the touch. The bottom one is warm. Top radiator hose is warm to the touch. With the heater fan on 1, it blows warm air constantly. On 2 it turns cool after a few minutes. On 5 it goes from warm to cool in about thirty seconds. The thermostat has been replaced with a new 195 degree thermostat. Engine is about 195 at idle. Driving down the road it fluctuates between 160 and 180. That makes no sense to me...


   
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even 160 to 180 should give you heat from the heater core if it has that temperature going through it. 130 out of the vent will feel hot to your hand. (not burning hot but it will feel like it will heat your car. If you aren't getting hot air from the vent there are a few things to check. The heater hoses to the heater core. are they both hot when the car is all warmed up? can you check their temperature? You could have an air pocket that gets caught in the heater core. you could have a partially plugged heater core. The GM coolant can plug up the heater core if there is air in the system over time.

the heater will always have hotter air coming out at lower speeds. the same goes for air conditioning. it will come out colder at lower fan speeds. It's because at lower speeds the air has more time going through the heater core or evaporator so it can transfer the heat. At higher speeds the air pushes through much faster so it spends less time pushing past the heat or cooling fins.

the next thing is the blend door. is the blend door moving to the correct position. you can scan the hvac system to make sure the blend door is operating correctly. Sometimes the motor will get stuck or lose the position setting. with a good scanner you can check and move the door to see if it is going all the way through it's cycle.


   
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