cooling problem

hello, i have a 97 lumina with 120xxx miles, and ive recently had problems with the cooling, for some reason my car overheats even when in idle, 75% of the way up the gauge. what could this be? is it the coolant or the thermostat. i was also thinking about changing my differential fluid ans well as my tranny fluid, but was told i could harm the tranny if oil wasnt changed in a long time. any advice would be appreciated. thanks.

Welcome to AF. Do you loose coolant, does the fan come on at 222 degrees, What is the actual temp it reaches before the fan comes on if it does? The trans and diff fluid are the same thing, is the fluid burnt?

I changed my tranny fluid and filter for the first time at 115,000, no problems...if the tranny is acting strange you may help it or you may ruin it by changing fluid, it's a toss-up. But if doing it just for maintenance, go for it. I reccomend only partial change, just what comes out with a pan drop and filter (should be 6-7 quarts), no full fluid exchange or flush...seems to aggravate them when they've been let go until higher miles like you have.

Are the radiator fans running while it's showing hot?

If using the A/C are both fans running contiuously?

Any sludge in the coolant tank, or air bubbles backing up into it when running?

First thing to do is verify that it's completely full, by checking the radiator itself, the coolant tank won't siphon correctly if there's a leak someplace, it could just be low and needing a fill and bleed, then find the source of the leak.

If it proves to be full already, then a thermostat may be your next best option...but generally when they fail, they fail completely, locked up and the motor overheats violently within a few minutes of running. When a 'stat is partially stuck, they'll usually run fine around town, but the temp will climb the longer it's driven at higher speed (reduced opening/flow can't keep up with demand)

Fan problems usually will cause it to get hot very quickly at idle, but cool off to normal as speed increases...if I understand you have high temp all the time?

Make sure you didn't suck a plastic bag or something up into the radiator opening under the front end, blocking airflow...