MKI / MKII S type 240 340 & Daimler 1955 - 1967

STUCK SHUT Thermostat Housing

Old 02-26-2019, 01:45 AM
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Default STUCK SHUT Thermostat Housing

Hi all,

After undoing the nuts and trying to remove my thermostat housing, I cant get the darn thing off! Do I need to remove the studs as well?

Trust me, I've spent a bit of time searching the net, my Haynes manual (which offers not a lot of advice here). Has any one else had any experience with this?

Thank you in advance!


Car details - 1964 Mk 2 2.4L
Old 02-26-2019, 02:10 AM
Glyn M Ruck's Avatar
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Likely corrosion or somebody got clever with the Permatex or similar. Apply lots of penetrating oil & let stand. You might even have to apply some local heat with a gas torch (carefully). Then a stiff clout with a rubber mallet to free. I would leave the studs alone.
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jaayman (02-26-2019)
Old 02-26-2019, 03:38 AM
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Try a wood chisel to pry the housing apart.
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jaayman (02-26-2019)
Old 02-26-2019, 12:22 PM
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Hold off with the wood chisel, you probably have the thermostat housing that has a long stud that passes through the 2 parts, this will be corroded I guarantee it, I will find a picture in a mo and add it to this post.

The stud is steel and the housing is aluminium, the two dissimilar metals react and corrode (galvanic corrosion), if this is really stuck tight you may have to remove the inlet manifold to get it off, if you use a chisel to try and part the two you will most likely damage the housing on inlet manifold.

Firstly are you only trying to get the top section off (81) or both (78 & 81)

Stud 75 is the long stud and passes completely through the thermostat housing (78) and the water outlet elbow (81) this is the main candidate for corrosion, with some penetrating oil and and little effort you can usually remove the water elbow (81) getting the thermostat housing off stud 75 can be a swine. The only way if the corrosion is solid is to remove both studs 74 from the inlet manifold and then gently tapping the thermostat housing rotate it back and forth, this will either unscrew the stud from the inlet manifold or free the stud from the housing if it breaks the corrosion up enough and you can remove the housing.

I have had to remove the housing with stud attached from the inlet manifold and then clamping the stud in a vice keep trying to rotate the housing on the stud and use some heat to help, you will have to get a new stud if you have to get that far. But if the stud has corroded, it is best to fit a new one regardless, when you put it back together put copper grease on the stud to keep water out, you can put an insulating sleeve on the stud but this needs to be thin walled and snug fitting, the idea is to electrically isolate the stud from the aluminium as it is the anode/cathode reaction that causes the corrosion, and there is a large surface area contact on this particular stud/housing.

Last edited by TilleyJon; 02-26-2019 at 12:25 PM.
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jaayman (03-05-2019)
Old 03-05-2019, 12:54 AM
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Got if off with a lot of penetrating oil and a wood chisel in the end. Thank you all for the input!
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littlelic69 (03-11-2019)
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