It is about -5 to -30C outside and I notice the engine temp usually hangs around 70 at the top end, after a 30 minute 100KPH drive. It hardly ever gets up to 80. I could use a little more heat in the car too. Is the thermostat defective? Last year I did replace that electric coolant pump, and the entire heater valve assembly.

This is a 1989 420 SEL.

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1989 420 SEL