I have noticed that if I let the car idle with the heat on the engine temp will drop into the 70c range. Thermostat is fine, I replaced it last spring and tested it in a pot of water before I put it in.

However my SDL does have good heat, once the temp gets past the second line on the guage (50c-60C?) the heat will come on and work well.

Today it is 20 out and she runs at he usual temp, right above the 80c line.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200