MG Tech – MGB Thermostat Replacement

Roger Taylor turns his attention to the thermostat, an occasional source of trouble with MGBs.

If the engine isn’t running hot enough it could be down to a fault with the thermostat so it is one of the first places to start looking for a problem

The thermostat is located in its own housing on top of the engine block close to the radiator and is secured in place with three studs and nuts. Before removing, detach the top hose leading into the radiator and place a tray underneath the car to stop any fluid over-flow.

The nuts and the housing itself, which comes with a gasket seal, can sometimes become corroded or stuck in place so you may need to apply penetrating oil to loosen things off.

Once the cover is removed take out the thermostat itself and examine its condition. The operation of the thermostat can be easily checked by placing it into a bowl of hot water. When cold, the thermostat will be in the closed position and should open when hot to allow water to pass from the engine into the radiator.

Some owners choose to change their thermostats to operate at different temperatures for the summer and winter. A standard thermostat operates at 82 degrees while there is an 88 degree alternative.

Once the correct operation of the thermostat has been established, or a replacement sourced, it should be re-inserted into place, a new gasket fitted and them secured in place using the nuts.

While doing this, it is also an opportunity to examine the condition of the hoses and connectors to and from the radiator for any signs of cracking, splitting or corrosion.

Finally, top-up the radiator with water and anti-freeze at the correct solution and run the engine – hopefully this will have solved the problem.

A new thermostat is a very cheap replacement part at £3.50 and the gasket will set you back all of 50p.