Started having problems with running hot a few weeks ago--first with the AC on and then pretty much as a regular thing. It's getting warmer here in Texas now, so don't know how long this problem might have been minimized by cooler weather. The radiator was replaced in 2006 so is probably not the problem. (I got this car from my father, who maintained it meticulously, all service intervals met--it is immaculate inside and out with 250,000+ miles. BTW, the engine was replaced at 150K by MB, so the rod bending problem should have been eliminated) I determined that the aux cooling fans were not coming on--did a bit of troubleshooting, cleaned terminals and managed to get the fan to come on when the AC is activated. The high-speed fan does not come on at all, even when quite hot. It has never exceeded 115c but used to run at a constant temp just above 80c. After fixing the AC fan took it for a test ride on a warm afternoon. Seemed to have reversed the symptoms--ran hot without AC, cooled down when AC was switched on. Now it's running hot with or without the AC on, and gets even hotter with the AC. I have verified that the AC aux fan is working. I did a bit of troubleshooting, and shorted across the terminals on the thermostat sensor. Fans powered up on high immediately. So as a stopgap I jumpered the two terminals to make the fans run constantly. Drove back home on the same hilly route I followed to my friend's shop, and it ran nice and cool all the way. But the AC doesn't work now, with the jumper across the sensor. I'm figuring to replace that sensor and the thermostat. Any other suggestions or similar experiences? Seems pretty straightforward to me. ===========