Engine cooling issues - need help [Archive] - GrandAmGT.com Forum

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builderofstuff
08-28-2010, 06:09 PM
I have a question regarding the engine cooling system in my 99 GT. I replaced the thermostat a while back and one of the radiator hoses and I've noticed that the car seems to run a bit hot, around the 215 range. However if I turn on the AC the engine seems to run cooler. Why would running the AC make the engine run cooler? If anything I would think it would be the other way around.

Chris

Malaclypse
08-28-2010, 06:46 PM
Your cooling fans do not turn on until the engine reaches about 216. That is, unless you turn the A/C on. In which case they'll run constantly.

That explains your car's behaviour. Perfectly normal.

AaronGTR
08-28-2010, 06:47 PM
That's normal. These engines are designed to run hot. The cars computer doesn't normally turn on the fans until you are over 220. If you turn on the A/C though it will turn on the fans to draw more air through the condenser in front of the radiator to help the A/C stay cold. Side affect of that is more air through the radiator and cooler water temps when you have the A/C on. ;)

builderofstuff
08-28-2010, 07:03 PM
thanks for the replies. what confuses me is that it never did that before, it would stay right on the 200 mark on the temp gauge.

Chris

turdstangjunk69
08-28-2010, 09:13 PM
I have noticed this on my car also. Only when I don't turn my a/c on and I goes in the over the 200 mark the trans shifts really weird. It shifts real hard. Kind of strange. I know my trans is shot but if it is cooler like under the 200 mark it is fine.

builderofstuff
08-28-2010, 09:15 PM
I haven't noticed any change in the shifting, just the temp change.

chris_gt_74
08-28-2010, 10:40 PM
I have noticed this on my car also. Only when I don't turn my a/c on and I goes in the over the 200 mark the trans shifts really weird. It shifts real hard. Kind of strange. I know my trans is shot but if it is cooler like under the 200 mark it is fine.


That's likely because of the fluid masking the transmissions failing. The cooler and thicker the fluid is the better it will shift. Once the heat gets in it and thins it out all the wear begins to show it's self in the shifting and roughness. I bought a car once in the fall and it ran like a champ, but the first summer I encountered I had nothing but transmission problems. All of which really showing themselves when it was hot.

AaronGTR
08-29-2010, 12:36 AM
^That definitely could have something to do with it. Especially since the trans cooler lines run to a core inside the radiator. That has two purposes... 1) to keep it from overheating if running the trans hard, and 2) to help warm the trans up to temperature faster since the engine coolant warms up faster than the oil or tranny fluid. Of course if the coolant is cooler then it cools the trans as well, and if you change the temp you change the viscosity.