'87 80 1.8 Heater problem

[Tom Nas]

Hi all,

Just thought I'd run this by y'all...

Patient: '87 80 1.8 carb.

Symptoms: outside temps just below freezing, engine gets hot (water temp
gauge hits 90 C) but heater blows nothing but cold air with knob set to
full heat. I get in a traffic jam, temp gauge goes to 100 C (I get slightly
worried) and suddenly the heater starts working.
Coolant level fine. Heater core doesn't leak. Heater valve appears to be
operational- I left it in the open position from arriving at work, didn't
fiddle with it until it refused to work. As soon as the heater starts to
blow hot, coolant temp goes back to 80 C (pretty cold, it usually hovers
around 88 C).

I'm thinking sticking thermostat. Any other suggestions?

When I drove over to a friend's house tonight (car had been standing for
two hours) the heater blew cold again, only to start working after driving
for three minutes. When I returned home three hours later it was warm from
the start, as I expected it to be. Coolant temp gauge was back to the usual
88 C.

There's no AC in this car, just the regular three-dial heater.

TIA for your replies!

Tom