Replace the radiator cap. If that doesn't help (at least to build
pressure), then have the system pressure tested at a radiator shop. The
overheat is because the pump is becoming air locked. Other
possibilities include a clogged radiator and compression leak (blown
head gasket).
Randall
Mark Purtell wrote:
>
> I just bought my first MGB-its a 1977, and I believe that it is 100%
> stock. The car overheats after driving it for 20-30 minutes, and then it
> will stay in overheat for a 1-3 minutes and then return to normal
> operating temperature, only to have the whole process occur again at a
> later time. I have replaced the thermostat (195 degrees), and the
> temperature sensor. I have noticed that the lower radiator hose doesn't
> build pressure even when the car is warmed up/overheating.
>
> Any suggestions?
>
> Mark
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