Maybe it is getting to 80, but the indicator is bad? Is there a way to check the temperature with a thermometer of infra-red device?

I have no idea how to diagnose / repair such a problem, but I would start at the temperature sensor. I am guessing it has a certain resistance at a certain temperature. Or could be a corroded wire connector at the sensor?

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport