That heater coolant valve is normally open at rest. Vacuum closes it. System was designed to flow coolant always thru the heater core, except when A/C set to max. Also, the butterfly flap in the valve, when open, is really only open about 30%.
Obs: Just read your car lacks A/C, so maybe there is no valve?
Test (or replace) the thermostat. Extended warmup times and lack of heat in cool weather point to that.
Could also be clogged heater core. Easy to flush. Careful with the hoses and inlet/outlet stubs.
More remote possibility: slipping impeller on water pump.
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1985 744 gle d24t
1985 745 gle d24t
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