So after having my 1989 560 SEL for 10 years I went in to do the thermostat today. I followed the tech page on here and I am pretty confused .... I don't see a thermostat. Is it actually located on the side of that housing and entering in sideways?

Also, the Coolant Sending Unit (?) plug vanished in the process - it must have already been loose. WTF! My fear is it actually fell into the what I thought was the thermostat housing. I can't find it anywhere. As usual a very simple job turned very frustrating - so essentially situation as normal in car repair.

So I guess the bottom line is, where the heck is my thermostat? And for the Sending Unit harness plug, if it DID fall down in there any ideas on the best course of action? But then again wouldn't it float ...

Thanks in advance for any help.

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If you really didn't have a thermostat, you would have had operating temperature problems that you would have clearly noticed.

I seem to recall reading that the W126 cars had the thermostat on the side, R107 up on top. Having just done the thermostat in my SL, the housing is very obviously different, it has a milled area for the thermostat to sit and a slot down the side for a weird brass rod that attaches to the top of the thermostat body.

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Might be that it was removed to try and "solve" a cooling issue. If you noticed that the car took very long to get to operating temp especially in cold ambient temperature that is a sure sign that you've been running sans thermostat. Not sure what you mean by plug missing as the sender connects to the "212 switch" which makes the fan come on when coolant reaches 212F/100C.

TH:

Yes, the stat is located on the right side of the water pump.
The top housing is only a hose connection and sensor location.

Thanks so much.

Can someone tell me what the single pole sensor is on the housing? The connector to this one broke off and is missing. The two pole is the coolant temp sensor activating the fan and the single pole is the temp sending unit which sends the temp to the dash gauge?

Also does that top housing have a specific gasket or just use gasket maker?

Sorry for all the questions ... I looked all over and couldn't find the answers anywhere!