MGB 77 – 80 Thermostat Housing Components
With the advent of an electric radiator fan starting in 1977, all the thermostat housing components changed. The thermostat housing is a cast Aluminum affair. It has a mounting lug on the outer end for mounting the air injection pump (for pollution control)
More importantly, it has a threaded hole on top. The hole serves two purposes: By taking out a threaded plug, you can fill the cooling system. This will allow you to completely fill the system, preventing air locks. (It is also kind of necessary since the radiator on late model cars does NOT have an opening for a rad capwhere you would normally fill a cooling system).
The original plug was made of plastic. In a severe overheating situation, it was common for the plug threads to fail. The plug would then be blown out of the thermostat housing, thereby relieving the cooling system pressure.
Too bad all your coolant would also “geyser” out of your cooling system though…
MGB Thermostat Housing Studs
The thermostat housing is secured to the cylinder head with three studs and nuts. The nuts are just plain old 5/16” UNF thread so we won’t worry about them. On the other hand, the studs are 5/16” course on one end and 5/16” fine on the other end. Good luck finding those at the Home Depot!
Thermostat studs should last a lifetimebut they don’t. The ingress of rusty water (otherwise known as coolant), leaks into the stud threads and rots them away.
We have new ones on sale now.
Fits any MGA or MGB. Three needed.