Your engine is now operating where it should operate.

Looks like you found a properly functioning thermostat. Rated temp is 87C. A proper thermostat should START to open in the 87C range and be fully open by 102C.

If your engine were running under 80C, that was because the previous thermostat was broken. It seems that as the thermostat ages, the opening temps seem to creep down a little bit. When my car starts running 80C on the highway, I replace the thermostat and that brings it closer to 90C 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