Weird cooling issues on 95 90

[Peter Golledge]

List folk,

I've run into a road block preparing one of our Steamboat cars... V6
powered 90.  Has had cooling issues (high temps at times, low at others)
since purchased a few weeks ago.  I figured thermostat, ran at 4 x
Georgetown lake events using cabin heat to keep things under control.

Pulled tstat (Audi... behind the timing belt... sheesh), put in coolant and
bled out the air.  Now the weird part, no hot flow out the thermostat pipe
even after getting more than half way on the temp gauge.  Cabin is getting
heat just fine so I know that coolant is flowing.   The return hose gets
hot from engine coolant back flowing a bit so there is plenty of heat being
generated.

I've tried a second tstat (tested both before after with boiling water,
working).  I've backflushed the radiator, flows well and clear.  The only
thing I can think of might be a water pump with a failed impeller, seems
unlikely given the cabin heat means some flow.

Any BTDT? Suggestions to troubleshoot further.