MG Car Repair: overheating 1500 mg midget, water pump impeller, head gasket leak

Question
Hi Howard,
Im having an overheating problem with my 77 mg midget. so far replaced bad fan clutch, thermostat, reversed flushed system and changed hoses. The car drives fine in city driving conditions. Different story on the highway for 20 minutes at 3000 rpms.It will quickly overheat at highway speeds. Any thoughts or ideas will be appreciated. Thank you. Joe.

Answer
Hi Joe,
First step is to go to any auto parts store and get the dye that is put in the radiator to test for CO in the coolant. This tests for any head gasket leak. If it shows negative accurately set the timing and and if all that is ok check the lower hose inside to see that the inner part of the hose is not separating and closing. Also check to see that the water pump impeller is not loose on it's shaft. If all that is OK you should have the radiator tested by a radiator shop to see if it is partially clogged.
Howard