Do aluminum housings fitdifferently?

[zhandax]

The bentley shows the o-ring fitted on the inside of the thermostat as seen on the left.

I replaced my plastic housing with aluminum and the only way it seemed to seal was on the outside as seen to the right (this is in the water pump; housing has not yet been installed).

Is the aluminum housing designed differently?

[RallyD]

I am needing to do a cooling system service on my M60.
Haven't looked to see if I have the plastic or aluminum, it may have been changed by the PO. If not, where did you source the aluminum housing from?

[winfred]

the aluminum is a direct replacment for the plastic, the o-ring goes on top of the thermostat

[zhandax]

where did you source the aluminum housing from?
bmaparts.com (or call Peter)