Thermostat

Hi Guys,

My SUV's heater is not getting any warmer like it use to have it. It is just a little bit warm that is it. I check my anti freeze and it is full, one thing that I knew while checking the anti freeze is that my upper hose is warm and lower is kind of cold and it's been running longer than 30 minutes already. I don't know much about heater system but I think my thermostat is not open. Can any one help to diagnose this heater system. How difficult to replace a thermostat in my SUV if it is bad "1999 Isuzu Rodeo 3.2" Thanks for advance.

I'm not sure how difficult it is in your year, I do know it's under the intake manifold.

Does sound like you need to replace the thermostat as well as radiator/coolant flush, sounds like the cooling system may have a blockage as well.

Make sure you ABSOLUTELY use an OEM Isuzu thermostat ONLY.

If its not heating up the t'stat would be sticking open, not closed. A t'stat stuck closed would make it over heat. What does the temp gauge say? One hose should be cooler then other, thats the job of the radiator. If your gauge is getting to normal but you arent getting heat, check the 'doors' on the heater core. These dont have valves on the heater core, just doors that mix the hot and cold air, they can come out of adjustment.

I havent done a t'stat on a rodeo yet but on 2nd gens ('98+) the t'stat is indeed under the intake plenum. Which means the plenum has to be removed to get to it. That means you probably will need new gaskets for it as well.