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Tech Article

BMW M20 Thermostat Housing Variations

Last Updated: 05/08/2021
Parts Group: Thermostat housing
This article discusses the thermostat housing (not the cover, but rather the main casting that bolts to the engine) for the BMW E28, E30 and E34 models with the M20 engine, with a focus on the variations.

If you are not here for the technical analysis but would rather buy a used unit from us, guaranteed to work and fit, then please select a link below.
The information herein is based on my own cars and used parts that I have bought from various junkyards.

Thermostat housings for the BMW M20 engine come in at least two variations even though the part numbers are identical on the casting, and in the tech literature I have seen.

For the large coolant hoses, the earlier style has smooth connection outlets and an outer ridge. The later style has ribbed connection outlets instead, probably machined into the casting. I can envision pros and cons to each of the two variations, and they are likely interchangeable.

I found the earlier style on a 1984 325e, and I found the later style on a 325i made in or after 1988. Where exactly the model year cutoff is, I do not know.
style element

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