Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
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Not a "modern GTO owner," but I noticed you have had the car 10 years. It has been my experience with these newer cars, that the radiators will eventually clog up and the free flow of coolant is not what it used to be. Learned this on a Toyota. Fans would come on when I thought they really should not and stayed on longer as well. Temp needle was just slightly over the mid line, so never thought much about it until it got progressively worse over time. Did the thermostat as well thinking it was going bad, but not much help. New air filter thinking it was restricted causing a possible lean condition.
Installed a new radiator (about 150,000 on it) and problem fixed, temp needle dropped below the mid point and fans generally never came on again. Put another one in at about 260,000 after I had a head gasket go bad and put oil in the water, and no water into the oil. Sold the car with 271,000 on it still running well. Have a 2015 Hyundai bought new with 90,000 on it now, and I will replace the radiator as it closes in on the 130,000 - 140,000 mark when I get there - just as a maintenance precaution.
So, it could be the radiator. Purchase an infrared laser temp gun at your local auto parts store (they are inexpensive) and you can "shoot" the cooling system at different points which may pin point any area that could be a hot spot and the problem area to look into.