I have been tracing this car and trying to incorporate the info you folks have provided. I never said the car should run at 80C or below. The car runs around 90C on the road. If we are to believe the mark above the 80C mark is 100C (the guage does not seem to be linear - no Mercedes ever has been in my experience), then my car is climbing to 105 -110 without the auxiliary fan coming on (at any fan speed). I have no doubt that it will continue to climb in excess of 120C if allowed enough time and high ambient temps. Bringing on the auxiliary fan (manually) brings the temp down fast. I have figured out that all the temp switches are on the thermostat housing. One seems to be for the ECM. One is for the guage. The two pole switch seems to be B10/8 for the auxiliary fan. With the engine cold the switch reads 3,333 ohms. At 85-90C it reads 525 ohms. At 90-95C it reads 415 ohms. At 100-105 it reads 331 ohms. There are two relays (K9/1 & K10) in the back of the fuse box that respond and start the fan when I jump the leads at the B10/8 connector. BUT, they do not seem to be "smart" relays that can recognize the difference in resistance at the switch. I think the sensor B10/8 may feed it's signal the the A/C pushbutton unit, and from there the signal goes to the appropriate relay. So far, I can only get the fan to run in high speed. I really need info on the correct readings at the switch to determine if it is at fault, or further troubleshooting help if the switch isn't the problem.