brett san diego

It really sounds like a blockage somewhere or poor coolant circulation for some other reason. Why would the temp suddenly rise like that and then the problem persist... assuming the new thermostat is doing its job correctly. Maybe it's worth removing all the hoses and confirming that there aren't any blockages in the hoses or their connections. I'm stumped. And, I don't think this would be a fan clutch thing (and it already doesn't seem to be since a new clutch didn't help).

Yes, the radiator and water pump are expensive guesses. How many miles on the current water pump? At some point, it will fail, and it will likely happen at the worst possible time. It might be worth doing it now as preventative maintenance. My water pump locked up at 115,000 miles. Fortunately, I was less than a mile from home and was able to drive the rest of the way before overheating.

I'm all out of help for now. I know you said you read out the coolant temp. from the sender using the climate control diagnostics (and it agreed with the gauge), but I would still be tempted to put a thermocouple sensor in a coolant hose to get an independent reading of the actual coolant temp. Good luck,

Brett

ijaen

I agree with Brett, when my old car acted like that it was the radiator that had a few tubes partially clogged and that impaired the radiator's efficiency a lot! After I installed a new upgraded radiator, thermostat, coolant pump and coolant temp sensor for the cooling fans the temperature behaved like it should.

sweat

Hi my name is sweat I on a 1992 300se w140 I'm loosing coolant from the back of my block the car has not overheated it has not lost any pressure and it does not burn white smoke my friends say it may be a head gasket but you brought up the T connection what is that and were on the block is it located. If thats the problem I would rather pay to fix that than replace the head gasket.

NZ_Benz

DO NOT DRIVE THAT CAR!!!!!!!! You must have caught it just in time, to be honest I have not looked at the 'T' connection on mine I just know it is at the back of the block somewhere. If you go to www.benzworld.org you should find a thread on it, when the T connection fails all hell breaks loose even if you pull over quick. I'm sorry I wish I was more help to you. You need to get someone who knows what they are doing to look at it ASAP.

Good luck.

doc willy

is the T connection related to heater circulation

a small leak in the heater circulation can cause overheating and coolant loss via the reservoir but since dont need heater in tropics we just blocked the flow to heater

also check for leaks in the windshield water reservoir heating tubes showing signs of discoloration of the windshield water