I have an update on my temp issues. I believe that members should write posts telling everyone what the problem WAS so that others can benefit from the thread.

Thus far, I have replaced the thermostat, upper/lower hoses, and the pressure cap. I still seemed to be running hotter than normal, but I have never gotten as hot as I did the first night (when I got to near 250F). Currently, in the heat - without the compressor on - I'm running a little over 180F; it will go up close to the 212F mark at idle at a stop light. This is in the day, in the 110F heat of Palm Springs. At long idle, she seems to go up to about 212F and stay there.

I had a pressure backflush today, figuring it was routine maintenance. The mechanics took a look at the system after the job. They said the water pump and fan clutch were operating fine. If anything, they thought I might have a problem w/ the auxilliary/condenser fan.

From that shop, I immediately drove the car to the shop that replaced my radiator core 8 mos back. They let the car idle for about 20 min and told me pretty much the same thing: the system seems to be running fine, but you might have an issue with the auxillary fan. Last week, I had the opportunity to speak with the owner of MotorWerks - which works on a lot of old Benzes - and he said that older Benzes often run hotter, and he also seemed to zero in on the auxillary fan.

This leads me to some questions:
1) My auxilliary fan DOES come on; but... it doesn't seem to stay on very long; sometimes it starts to turn and then stops; it doesn't seem to come on when the car is getting hot at idle; and, I've had the A/C on the last two days, and pulled over and checked, and it wasn't spinning at all. Does anyone have a clue when these infernal things are supposed to work?

2) I would like to begin by replacing the 212F fan switch.
where is it located? I have a 77 450SEL. Is it mounted on the dryer - which is located on the condenser to the immediate right of the fan? If so, my switch has two prongs.

3) Does an improperly functioning auxillary fan seem to explain my car's running at about 180-185F (maybe plus a couple of degrees) and idling at near 212F?

4) How hot does your car operate in city driving in hot weather? (Keep in mind, I'm in Palm Springs; last week we got to 122F. A COOL day in July/Auguse will run you 106 plus.

5) Does anyone know of a fan switch rated below 212F, and if installing one would be a bad idea? I would be willing to trade a little power for cooler operation.

I'm actually wondering if I really have a problem, or if I'm just paranoid. I may have had a bad thermostat, improperly burped the system when I refilled, and subsequently corrected the issue. But meanwhile my auxillary fan (or the 212F switch) was going out. In any event, I would much rather mess with an auxilliary fan than with a water pump install.
Mike

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Love driving my '77 450 SEL!
124,000 miles