91 toyota 4runner 22re manual 4 cyclinder. Having Problems with my thermostat gauge fluctuating up and down. Also, when i go to the mountains or im on a steep incline for a long period of time changing from first and second frequently engine will start to get hot. Changed thermostat yesterday but still having the problem. Any suggestions on things I could check? Or maybe you know the problem? Thank you

 

Possibly an air bubble in the cooling system. Do a search for "burping" the cooling system. It can apparently be tricky to get all the air out.

 

I had a similar problem with the 3.4 when going up into the mountains, that one turned out to be as simple as a radiator cap.

 

First: familiarize yourself with how the cooling system works: http://www.arrowheadradiator.com/pre...aintenance.htm

then read the other articles that address overheating.

Fluctuating coolant temperature indications most likely malfunctioning indicating system, but possibly the thermostat.

Climbing hills that require first and second gear is hard work. You will be sweating. Your car will be putting lots more heat into the cooling system. My guess: your radiator isn't up to the job. Clogged arteries and weak lungs. At really low road speeds, maybe the fan isn't moving enough air across the radiator.

 

I have had my truck almost overheat a couple of times from just a simply dirty radiator (Lotttts of mud) I sprayed it down for $0 and no more overheating