My 1994 E420 has a strange problem with its engine temperature. In everyday driving, the temperature usually hovers between 82 and 100 on the gauge. However, if I have been driving for a while at 75-80, and then hit bumper to bumper traffic, the temp can go as high as 110. At that point, the high speed fans come on, and the temp drops to just below 100, but this can fluctuate back and forth. My mechanic does not believe that our mild climate (San Diego) should cause the temp to rise above 100 in just about any driving condition.

I suppose that my question is really two-fold:

1. What is the "normal" operating temperature range for this car, ie., is an occasional spike to 110 considered normal?

2. If this is not normal, why is it happening?

About one year ago, I replaced the radiator due to the plastic neck issue. At that time, I had the radiator filled with Mercedes red antifreeze at a 50/50 mix. This has probably shifted a little to the water side as I have topped off the reservoir a couple of times, only using water. After this temperature problem started, the mechanic replaced the thermostat, hoping that it would take care of the problem. Just a couple of days ago, he replaced the fan relay, since he believes that the fan clutch is operating normally. He does not know of any other variables which could cause the car to behave this way.

I greatly appreciate any assistance that the knowledgeable members of this forum may provide. FYI, I also started another thread concerning the proper way to maintain the throttle valve actuator, again seeking some good advice. Have a look if you might be able to help.