My E320 wagon with 208,000 miles the temp has been a concern since I got it. When I bought it the temp sensor was showing it as running at about 45 c, replaced the sensor and since then have had even more headaches. Replaced the thermostat three times til finally I have one that is a 79c, replaced auxiliary cooling fans with new. What it does now is when I start it and drive down the road the gauge reads at about 82 and stays there like a rock. However, when I come to a stopping point, a light or anything else then the gauge begins rising, once moving again it goes down a bit, but will not read much below 85-90 and the more stop and go driving the more erratic it gets. Went up above 100 yesterday while driving at about 50mph. When I stopped I could hear the cooling fans running at high speed so they are working. If I turn off the a/c it will creep back down but the system should be able to handle cooling with the a/c on. It does til it is at a stop. The water pump and headgasket were replaced at 38,000, a/c pump and related equipment were replaced in 2008. I have read on this forum where temps above 100 are acceptable. It's not the temp so much as the unpredictable rise that worries me. I am shopping for a new water pump and that will be the next project. Is that the cause of the problem or should I also be shopping for a headgasket set?