96 S320 Operating Temperature
 

I am in Northern California and on hot days when it is around 85 degrees outside, my temperature gauge on higways reads around 90 and on stop and go and lights it goes to approximately 102. Is this OK or is the car running Hot.

At Stop-n-Go I usually turn off the AC, the engine temparature gets down by 10F.

Your temp seems to be on the borderline but still looks OK to me.

at 95 to 100C, after having gotten off the freeway and in stop and go traffic, the Aux (electric) fans should be on and the fan clutch should be starting to lock up. you should notice the increased engine sound when accelerating from a stop.

My E300 was right below 100C after getting off the freeway today; it was 98F outside.

Question
 

Let's say you have a fan switch that activates at 99c.
At what temp does it turn off? Just a degree or so below 99c or much lower?

W140s have a five stage electric fan system. Fans will come on with different speeds depending a wide range of scenarios.

It is normal for your engine temperature to rise up to 100c on town driving or after getting off a freeway, more so on hot days. Although, just before reaching 100c the electric fans should kick in and lower the temp back to 85.

The processs will repeat itself if you continue driving on stop and go traffic. Once you get back to high speed the temperature should level around 85.

Dumb question: When was the last time the coolant was changed? I did a flush & refill with a 50/50 mix of MB coolant and distilled water and my S320 was much happier afterwards. I just got back from Orlando, FL (took the Auto Train!) and the car stayed between 80*c and 90*C the entire time we were there. Even in stop & go traffic with the AC turned on.

Alledgedly, water cools better than antifreeze. So if you are running 100% coolant, you might try reducing it to 50/50.

I'm still looking for an answer to my question:
Let's say you have a fan switch that activates at 99c.
At what temp does it turn off? Right at 99c, just a degree or so below 99c, or much lower?

Check out Menu#17 (in the aqua colored table) on my web pages for some common things to do that will lower your engine temperature.