No heat until engine runs at 2500 rpm or more,temp gauge up when at idle,

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Low coolant level, water pump impeller worn or slipping on the saft inside of the engine are a couple of things that come to mind!!!!

I changed my water pump thinking that was the problem, it wasn't, but the pump is easy to replace, could also be the thermostat sticking open, going to change that tomorrow, just saw an article about a heat door , going to research this, but it requires taking the entire dash apart

My car has similar issues, but I have notice that my cooling fans will not engage unless I have the A/C engaged. Otherwise, the engine will overheat with the cooling fans off. Changed both relays and that did not solve the issues. My car overheats sometimes at idle or stopped in traffic, over heats a low speed, stays cool at high speeds, unless going up hill. Strangely, if I run at high RPMs going up hill the engine does not overheat as fast or not at all. I am wondering if the 280,000 miles has a lot to do with it. Engine wear causing it to run hotter than normal.

I have a 2006 Pontiac torrent. The heat is not working but the air works when I am driving but now my fan is not coming on to cool the engine off because it runs hot when its stopped for a period of time. Would really appreciate some help. I have codes showing p0030, p0201, p0443, p0481

What is causing the cooling fan to not work Thanks