I recently replaced the thermostat in my '89 300E. All is well but I have noticed that when the engine is shut off and restarted a few minutes later, the temp. reads above 100 deg. As soon as the engine is started, the temp. comes right back to normal. This never happened with the old thermostat. What is different????

Maybe the old thermostat was bad, engine temp should increase as described for 10-15 minutes after shutting off.