Not sure how, or why, but some of these cars have Federal measurements instead of metric on the temp and oil pressure gauges. Here's my '79 cluster:

http://i.imgur.com/5EduQuQ.png

yyup... from 77-79 the clusters were SAE... not metric...

Ha didn't know that. What about the latest Mercedes imports to USA, is it SAE or Metric?

The only way the OP's car can go up to 250F idling "for a while" is if the coolant was full and not moving. If the coolant was low (below the sensor), the gauge would get a low (not true) reading.

The latest MBs do not have instruments like the older models.

Starting with the 210 they dropped the oil pressure gauge.

The new models have water temperature in the cluster menu.
My 164 water temp is in degrees C.

The fan clutch can cause overheating. Basically it will be turning, but slipping to the point where it is not turning fast enough to draw the correct amount of air across the radiator and condenser. when engine exceeds a threshold temp (temp sensor/threshold is designed into the clutch), the fan speed should increase. Access to an optical tachometer should show the fan at the same speed as the pully driving it when engine begins to overheat. If it is slower, then the clutch is bad.

good info can be found here:
Diagnose Cooling Fan Clutch

Good to know the years. Mine was the only one I'd seen in person with that cluster. Also, the only non-turbo amongst my friends.

Where did you aim the IR thermometer? If IR was reading 230F after idling a while, then it confirms your engine was at 230F and your gauge in the cluster was not off by a gross amount. Again, how long exactly is "idling a while"?

Your friends aren't true friends if all they drive are turbos :P

I have two and never ever would dirty my hands on a turbo :D


I second looking at the fan clutch...I would also confirm there is a belt on the water pump....You can do the carrot test with the fan.....put a carrot in the fan....if it stops the fan....bad clutch...

Okay so I just ran it for a bit to see how long it would take to get up to where it was at yesterday. After 15 minutes it was at about 175 (Infrared and car thermometer), I ran it for another 15 minutes and this time there was very little variation, it went up a bit but stayed relatively constant. This is not what happened yesterday when it climbed into the 200s and I haven't done anything that would affect this... So I don't really know what's going on... I tried the "carrot test" for the fan, definitely passed that. There is another smaller fan on the other side of the radiator (front of the car) that as far as I know hasn't gone on at all, I'm not sure what this does and if it's supposed to be going on. But given these results I'm not really sure where this leaves me, I'm gonna keep an eye on it to see if it starts running too hot again, but other than that I don't think there's much I can do... Thanks for the help, unless any of you have an idea of why it might've changed behavior I'm just gonna keep watching it and let you guys know if anything changes, thanks so much.

Grab the water pump pulley by hand and try to turn it. It it turns, the belt is too loose.

Really is sounding like you have air in the system. On the early models there is a bolt on top of the thermostat housing, that needs to be undone when the car is idling to allow the air to escape....or do like I do, undo the top radiator house and fill with coolant...then connect it back to the radiator..