According to Roger, one of the most problems to crop up regularly on MGBs is a poor heating system – one of the prime causes being a blocked heater valve.
The only way to trace this problem is to remove it and check – something which must be done when the engine is cold.
First it is advised to loosen the radiator pressure cap, then place a large tray under engine before undoing the lower water hose (water pump end) to drain down the engine block.
Then cover the distributor to stop water entering from the top when removing the valve itself which is located on the side of the engine between the spark plugs and just above the distributor.
If the aluminium valve is blocked (above right) or shows signs of corrosion it is best to fit a new unit (below) rather than clean out the old one.
Use a new gasket when fitting the new valve and then adjust the operating cable to ensure the value is opening and closing properly. This is best done with someone working the dash knob for fine adjustment.
The other problem with heater valves is water leaking past the seals inside. When checking the engine fluid levels on a regular basis, it is worth running a finger under the valve (when the engine is cold) to check for dampness.
Sometimes a bad leak of coolant drips into the distributor causing misfiring and here again a replacement is required as well as checking over the distributor.
Finally, after fitting the new valve re-attach the water pump hose and refill the cooling system taking care to check the anti- freeze strength. Run the engine and check for leaks.