Thread: Coolant temps 2007 Grand Prix SC - Normal?

Are these temp readings normal for the stock temp gauge? Blue line to orange line is the range the car stays in during cold day (40 degrees or so) highway driving with heat on, car will go up to red line when idling before the fans kick in, will move down to orange line, then repeat. The car will normally stay between the orange and red marks while crusing at highway speeds in warmer (80 degree) weather.) I don't have a scanner to check the actual temps for the motor, although I don't remember the gauge ever going this high last summer.



Car is bone stock, 195* thermostat, no PCM mods. I already replaced the thermostat, temperature sensor and bled the cooling system, none of which seemed to make any difference.

When I'm taking trips on the highway I also normally see transmission temperatures in the range of 217 to 228, and have seen the thing go as high as 240 after driving up a steep hill with a loaded car. Is this really normal???

I'm really thinking that the radiator in this car might be partially clogged or have been replaced with a lesser model's (non-SC) part before I bought it (the front bumper and hood were resprayed but the radiator support has not been replaced. The bolts look like they have never been removed but I'm not sure).

Is there any way I can tell if the radiator was replaced (part numbers, thickness.)

What's the best way to flush the coolant on one of these things (drain & fill radiator only??, professional stealership flush??, use additives??, switch to non-Dexcool worth the hastle??)

Am I missing something or just being really paranoid?

Sorry, I know there are a lot of questions here.

I have a 2007 with s/c I put a aerogauge on it , the fans kick on at 220 and kicks off at 200, trans temp runs a little over 200.

Originally Posted by Liquifire

First off, are your fans working correctly? Second, it is hard to tell if there is no problem if you are not sure that your gauge is accurate? Maybe try switching to a 180 degree thermostat? I prefer non dexcool coolant in my vehicles. I don't know the best way to flush these systems. I just ordered aeroforce gauges today, so I don't know what tranny temp my car is running at now. Maybe only one of your fans are running? Maybe the gauge is off? is there proper voltage at the fans when you are up to running temp? Is it under warranty yet?--Mine is older so I don't know if I can help you otherwise.........

Both fans will run at low until it reaches about the red line marked above, then they will turn to high and the car will cool back down to the orange line above. I highly doubt that both the coolant temperature and transmission temperature gauges are inaccurate (1 or the other maybe, but both?) My larger concern is about the transmission baking at 220+ (usually it stays rock solid at 228, goes down if I slow down, goes up if I'm pushing the car harder) every time I take it on the highway for 30 minutes or more doing around 75mph in warmer weather (80 degrees plus.)

Car's voltage is always between 12.5 and 14.8 volts, I don't think there is anything wrong with the charging system (no dimming lights, always starts strong.)

Car is out of warranty.

i was having a heat problem too not to severe but cooler therm an a trans cooler will fix

Thats pretty much what my 04 non-sc does. I have been told by several gm dealership techs. that those readings are nomal. I had the scanner put on mine and the exact middle of the gauge (just a little above your blue) was about 201 degrees and about where your red is about 222 degrees (fans kicks in at 223).

I was worried too because the gauge was so jumpy when the car was stationary. Also i plan to have my fan turn on point dropped to 210. As far as the t-stat I would keep the stock one all 180 degree one will do is open earlier your car can still get up to the same temps.

The 3800 III is designed to run at hotter temps. for emissions, gas mileage, etc. If your vehicle runs too cold its actually bad for the motor. once warm the temp should not go below 195 degrees.

got a 05 and my trans started running at 221 is that normal