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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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]