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:

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

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

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

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.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

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 OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

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.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

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"?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

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

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


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.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

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..

__________________