The thermostat on the car is an 87C thermostat. That means, according to specs, that it starts to open at 87C. It will not be fully open until 102C is reached.

The reason that the car was running at 80C is that as the thermostat gets older, it gradually starts to open earlier and earlier. I replace my thermostat almost every time I change the coolant. When new, it always runs at 90C and up. Byt the time it gets to be about 3 years old, the engine starts running a hair below 85C if it is winter on the highway.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record