So my 1988 560 does not use normal thermostats, the round ones do not fit because of a screw that is holding the houseing, so the thermostat need a grove in it. Any idea what i might need? My car is from miami, and the 80c euro thermostat did not physically fit. My did not have one installed, so looks like someone earlier ran into the same problem as me, could be its from another m117. Part number on the housing is: 1172012630

I figured out that the previous owner had fitted a 79-85 5L thermostat housing, so found out why it does not fit.
Is this an indicator that the previous owner changed out the whole water pump? He would have to have done the chain as well then?

Sondrusen, what chain are you talking about? As far as I know, no chain is associated with a water pump.

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Fred Hoelzle