I have a 2002 Chevy Venture that the heat doesn't seem to work well now that it is getting cold. We had this issue last winter as well. It would take a very long time get the heat to finally come out warm but not very hot. I have tried the heat several times throughout the summer and fall and it worked fine ( pretty hot ). Now that it is getting into the 30's it is acting up again. I was wondering if there are any easy checks to find out what is happening. The coolant level is full and I never seem to lose any coolant. The cooling system appears to be running fine and reaches temp. on the gauge fairly quickly. Blowers are working. This has rear climate control so I am assuming there is a blower/heater core in back as well. I don't think it is hot back there either. I guess the question is what would be the steps in troubleshooting this. Thanks

 

I know this is a couple days old, but oh well.

I would start by replacing your thermostat. It may be defective and not allowing the coolant to heat up suffuciently.

 

Another thought is plugged heater cores I had one that just wouldnt put out any heat no matter what I did. The heater core began leaking and after replacing it there was all kinds of heat. You might back flush it and see if that helps.

 

Has anyone ever changed the thermostat in the Venutre with 3.4l engine. Looking at the repair manual it shows removing the exhaust manifold and a bunch of stuff just to get at it. I looked under the hood quick and it looks like it is buried under there somewhere.

 

I'm showing it under the air cleaner duct. Follow your upper radiator hose to where it attaches to the engine, the thermostat is under it.

 

One thing to try is, let it get to normal operating temperature, turn heater on with engine at idle, and feel temperature of heat coming through vents, then rev the engine a little and keep it at a steady rev and see if temperature feels hotter when engine is revved. If yes, that's usually a good sign of restriction in core(s), or a weak water pump, but I'd lean toward restriction in core. I had a Caravan experiencing same thing, and ended up circulating "CLR" through the core, with a drill pump, then letting it sit in the core overnight, flushed it again, then switched hose and back flushed as well. Re-installed hoses on core, topped up coolant, bled system, and had 75% better heat at idle, or low speeds. Much cheaper to try than replacing a heater core.