4.2l running hot, reduced power

[RedMonte85]

My 2003, 4.2l envoy seems to be having issues. Reduced power, lower mpg, and the temperature gauge is reading at 1-2 ticks above the 210 mark whereas all the years I have owned this vehicle, it always read at 1 tick below 210. Last year I replaced the fan clutch and water pump and about 40K miles ago I replaced the thermostat. I am thinking the thermostat probably needs to be replaced again. I have read about folks needing to have the PCM flashed for a fan clutch update but I feel like my fan clutch is working properly, roars at start for maybe 5-10 seconds and idles down after. Does this sound like a bad thermostat to you guys?

I have switched the headlight relay and the fan clutch relay to eliminate the possibility of a faulty fuse. I have also made sure there is no air in the coolant system. Thanks for any help

 

[Matt]

My guess is that the thermostat is stuck closed...very unusual as they tend to stick open, but it happened with mine. Change it out.

 

[Sparky]

Also just for kicks check the cat. A plugged up cat can lead to it running bad and maybe even hot. I know a plugged cat can get ridiculously hot in of itself (friend's plugged cat on his old car years ago was scorching his carpet and burning the weeds in the gravel driveway where he parked).

 

[RedMonte85]

How exactly would I check for a clogged cat? Exhaust seems to be moving out of the tailpipe freely

 

[Mooseman]

A backpressure test. Exhaust shop should be able to do this.

If you previously had low temperature issues, it may have clogged it. Check that the lower hose from the thermostat is getting hot. If not, it may be defective.