Try driving it around, and with the AC on.

You may have nothing more wrong than a radiator which is clogging up, aux fans that aren't working, a bad fan clutch or similar.

Of course, the temp sender could be bad or intermittent too.

What I do in these situations is take a cheap $5 digital meat thermometer. Duct tape it to the top hose of the radiator. You can use this to validate temp gauge readings.

Drive it around. See if you can make the temp climb. If it does, verify that it is actually climbing via the meat thermometer.

Once we verify that it is in fact overheating, we go from there.

erhard, welcome to the forum. You should post your additive question in a separate thread if a search has yielded no results.

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition