Today I got a weird overheating problem driving my '94 G350TD. (OM603 Turbo)

I was driving normal highway driving when I discovered the temp gauge a hairline from the red field on top. The gauge has been acting up before (electrical problems), but this time it was "for real".

I turned the heater to max, temperature dropped a little, pulled over as soon as possible, heater on max, let the engine idle and opened the hood. I found the radiator ice cold (ambient temperature around freezing point) except for the tank on the top left where the upper radiator hose enters. Cooland level OK, coolant cap had not vented any.

Tried squeezing the upper radiator hose a couple times, nothing happened, but the hose felt like it was a vacuum inside. Did the same to the lower hose, and suddenly it felt like a plug "let loose" and coolant flow started. Radiator got hot in a matter of seconds and temperature gauge dropped fast to the normal level. Waited for a couple minutes and started driving again. Gauge rised again, I pulled over again when the gauge reached about 100C, did the same, circulation started again ++

Had to do it this way (pulling over every 5 minutes or so) to keep it under 100C the rest of the way home.

What could be the problem? It's not the coolant freezing in the radiator, the coolant is measured to have a freezing point of -35C.. No air/oil in the cooling system.

I'm thinking towards a thermostat stuck closed and the squeezing of the radiator hoses "loosening" it for a while, then it closes and gets stuck again.

Any other ideas? Like I wrote, the problem suddenly occured, never had any overheating problems before, even on hot summer days uphills with heavy loads..

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'95 E36T AMG (124.092)
'98 E200T (210.235)
'00 E430 4Matic (210.283)

Agree with you on bad thermostat. The extra pressure from squeezing the hose probably pushed it open.

Please keep the post updated through and until successful repair. This is an interesting problem...good luck!

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