Thermostat housing fitment

[MrPhatBob]

I have a slight issue with my thermostat housing, the mounting point on the head:

Seems to be missing a spigot ring because the seal on the housing sits in the middle of an empty space...

Have I missed something here, is the housing wrong for the head, or have I lost the ring, or something else stupid?

[1998ccc]

The plastic thermostat housings came on the M44.  Have you tried the Al M42 version??

[MrPhatBob]

I'm not sure that I have one. This is a very late M42 engine from a 318ti which has a lot of the improvements that the M44 had, so...

[MrPhatBob]

Yup, I should have one of these shouldn't I?

[1998ccc]

AFAIK the late M42's still used the aluminum thermostat housing but got the better head and timing bits.  I've read the late late m42's got the lighter M44 type rods.

[MrPhatBob]

You're absolutely right on this, I had better look through my spares, and failing that - buy a new one!

[steel330i]

You're absolutely right on this, I had better look through my spares, and failing that - buy a new one!

I have a spare t-stat housing...let me know, $20 shipped

[DesktopDave]

Aren't those housings directly interchangeable? That later 95deg thermostat always seemed a bit too hot for me; I'd replace it with the early 88deg unit. One more thing - the thermostat doesn't need a bleed hole with the alu housing, it's a small passage cast right into the housing.

Don't forget the o-ring and gasket. IIRC it's thermostat, then o-ring, then gasket, then housing. Be sure the bleed passage on the alu housing is clear. I've seen a few owners cut the paper gasket at that point so it doesn't clog the passage but I've never felt the need. I almost totally avoid RTV with these motors, but I'm quite fond of non-hardening gasket sealer/dressing (Hylomar Blue or M, Permatex #2, etc.). They help a bit with re-assembly and seem to prevent leaks down the road.