I'm a new member to MCF, and I have to say congrats on the forum its great!

I'll get to the point, for the last several weeks I've noticed that my 99 LS is overheating while in idle or in heavy stop and go traffic. Once I get up to 30 MPH the temp goes back to normal. I have decent general mechanics knowledge and I noticed that the radiator was corroding and needed to be replaced. I've replaced the radiator, the radiator cap, and the thermostat is only 1 year old. However the problem still persists. I read in some of the post that it could be a problem with the electrical fans, but I can hear the fans kick in and the air conditioning works fine. Ive inspected the car for leaks and haven't found any. I'm out of ideas. Any suggestions that can help me out?

Thanks
MR

 

Is your thermostat opening? Sometimes a brand new thermostat can be bad/defective. Ive seen it happen. There could also be an air bubble in the system somewhere. You could also have a blockage in the system somewhere or it can be all gunked up inside. Here is what I would do. Drain the coolant, pull the thermostat out and bolt everything back together so coolant can still flow. Get a pot of boiling water and drop your thermostat in. If it opens, its fine. Next, geta hose and flush your radiator, with the petcock at the bottom open, just run hot water through it until only clean clear water comes out the bottom. Close the petcock and start your engine. Let it run the water through for a bit then shut the car off. Open the petcock then restart the car. Keep the hose in the radiator and keep it full of water, Just let the clean water flow through your engine until all the gunk works itself out. One thats done, reinstall your thermostat, close the petcock and fill it back up with coolant. Be sure to bleed the system of any trapped air.

 

Normal 0 Thanks for the advice! I didn't feel confident doing the work myself and took it to a shop. The result was that the catalytic converter is plugged and that is what’s causing the car to overheat. Who would have thought? To make maters worse the catalytic converters are back ordered and as of July 1st California passed a new law that says aftermarket converters can't be used unless they meet OEM Specifications.... What could have been something simple turned out to be an ordeal. So I have to wait for GM to make more or drive the car until it dies.

 

Not sure if this applies to your car but I know for the 00-05 montes gm has a problem with the cats plugging. Same thing happened to me with my car and after hours of searching the internet found a recall that covers the plugged cat if the car has under 100,000. I took mine into the dealership and got it back the same day. Don't have emissions where I live though.