Right side of engine, above alternator - you will see the housing where the big hose goes into it - that is the thermostat housing.

There were two housing types made. The original one is no longer made and if you need to replace the thermostat and yours still has the original housing you will need to buy a new housing too but if you get the PN off of the housing a dealer will be able to tell you if yours is the new one or the original one - there is also a VIN cutoff after which the new one was used too I think. It costs around $25 to replace the housing to the new one, if needed, IIRC.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz