Firstly it is not overheating if it isn't steaming or losing coolant, but it
may well be running hotter than it should.
You cannot change a distributor, keep the orientation the same, and expect
the same timing. You must re-time it, and you should have checked the
timing anyway. All MGB distributors are vacuum advance, the only difference
is that prior to 1971 all cars had carb vacuum, after that North American
cars used manifold vacuum. The difference is that with carb vacuum there is
no advance applied at idle, only off idle. With manifold vacuum advance is
applied at idle. But they both work the same way - the more the vacuum the
more the advance.
2nd on all factory cars the electric fans went off with the ignition, so you
have an after-market or PO bodge. Ditto the sensor in the bottom hose, all
factory cars had the sensor either in the head by the thermostat or the top
of the radiator. Likewise you cannot assume a PO temp gauge is any more
accurate than a factory gauge, and is more likely to be less accurate.
Modern cars often have the temp gauge controlled by the ECU, which maintains
a steady reading unless the engine temperature goes outside certain
parameters. This is to prevent owners getting paranoid about small and
normal temperature variations that the MGB shows.
Do you still have the mechanical fan as well? If so check the orientation
of the blades on that, and the orientation and direction of rotation of the
electric fan. A friend has a 1980 MGB that seems to have had similar
problems, as the PO fitted an engine mounted fan, bypassed the thermostatic
switch, and all sorts, but it was still boiling over. The rad cap was only
7lb instead of 15, and when I pressure tested it was only resisting about 4
lb anyway. And the engine mounted fan was blowing the wrong way i.e.
towards the radiator, but since it is so far away from it we decided to
leave it where it is for the time being.
Pt. 2 follows
----- Original Message -----
OK, I've had a problem with the BGT overheating for some time.
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