Are thermostat housings held in place with 3 bolts? Or 3 studs in the head?

I notice I've fitted bolts to retain mine, but perhaps I did that due to the studs being to short once the passenger side engine stabiliser bracket went on over the top of the housing?

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http://www.youtube.com/user/Hanras

I've seen both! Possibly studs were original though.

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1963 Morris 850 Smoke Grey
1963 Morris 850 Shadow Blue
1965 Morris Mini Smooth Van
1966 Morris Mini Van
1969 Morris Mini Deluxe Resto
5/72 Clubman Gt

Usually studs, but bolts will do it as well. Its more or less the same outcome.
Trouble with bolts is that you will try to sneak the bolt down tight without knowing you are going beyond the bottom of the thread hole in a delicate area, specifically the front hole. You can split the head right there and/or shear the bolt off neat.

Studs you take your time putting in with the thermo cover off nice and gently. Then you can tighten the nuts down without worrying about turning the stud too hard down the hole.

Another thing with the bolts you choose. Be careful of the thread type. The studs holes are UNC, whereas nuts are UNF.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

The bolts I've been using for the last 10years or so are stainless and seem to fit fine, however I do recall many years ago having coolant weeping up the thread and seeping out from under the bolts head. It sort of appears the studs have a non threaded section which may assist blocking coolant? The bolts I have are totally threaded.

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http://www.youtube.com/user/Hanras

Its quite common.

The gap between the water jacket and the bolts are narrow, so water can bleed through the thin bit of gasket and work up the bolt holes to the top of the thermostat cover.

Sometimes this is made worse by corrosion on the surface at this point making it difficult to keep a seal, even with a good gasket and some goo.

The studs aren't meant to fit neatly into the thermostat cover enough to form a seal, this is accidental if they do.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Righteo. I think I'll stick to bolts as I'm concerned once the engine steady bracket and radiator bracket go on, there may not be enough thread left over.....

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http://www.youtube.com/user/Hanras