This morning started out okay. Some heat for the first 20 minutes then it was barely warm. What's strange is that the engine was reading half a needle width below 80C when there was some heat and a needle width above 80C (normal) when I lost heat. It usually goes just past 80C and stays there. This is the first time I notice an interim steady state. I mean it went straight to the lower setpoint and hung there for a few mintues of freeway cruising before creeping to the normal temp.

Maybe a faulty thermostat is causing the engine to run cooler until the car sees freeway load. But it doesn't explain why the heat goes when it gets to operating temperature.

BTW, ambient temp as indicated by the car's thermometer has been in the high 40s F thus far.

Dave, I know a good guy for soldering. Are these microcracks obvious to someone who understands electronics? Are there specific traces to check?

Sixto
91 300SE ... brr
81 300SD