Heyo, cooling issues aren't typically something you run into in the midst
of winter, but this isn't a bad time for it either- far better now than
stuck on the M5 with your temps at redline.
As I read through the description, I thought immediately a thermostat.
No, you removed that and it tests fine. Hmm.
I next thought water pump as it sounds like we're not getting any
circulation through the system. You pulled the pump and verfied the thing
was working. I had the odd thought the impeller blade assembly had come
off, which is highly unlikely, but has happened before since it's a press
fit assembly.
So, you have no water going through the heater. That's not critical, but
it's a decent indicator of something blocking or no flow. You aren't
losing any amount of coolant, so I'd rule out a head gasket leak or any
leak at all really. That's good.
You might try bypassing the heater core completely and just loop the
heater hose right past the valve assembly. Just don't include the heater
in the circuit at all so it's only got the engine cooling. Check and see
if the problem still remains (high running temps). At least you can
separate the systems and determine which half is causing the problem.
I swear it sounds like the impellor isn't turning on the water pump. When
the engine gets warm, is the upper hose warm and the lower one cold? That
would confirm a blockage or lack of circulation. I don't think a
pressure test is going to help here in this case.
-Vegaman Dan
-1968 Mk III "Giles"
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