It is winter (12-22-23) in Massachusetts. Love my Olds at 138K it drives and runs like new. I am now 68yo and stopped the hands on mechanics, but I do have a top local shop. I am close friends with the owner, who has done my wheel alignments for years.

POOR HEAT. Which does NOT mean none! But lukewarm. Why I do not know. Engine appears to be running cool, temp gauge works, but barely makes it to the first hash mark? Should be just shy of the second mark. I personally change coolant and back flush heater core, just did it this past summer. I seldom drive this car, prefer my pick up as everyday ride. Had AC converted to 134A ....works great, as does everything else. Blend door actuator works fine.

Mechanic went right through the cooling system: new thermostat, back flush heater core, new coolant, checked for leaks & tightened all connections. No change?

Something is weird ? Any help?

LOU

 

Still sounds like a bad thermostat. Check the temp at the thermostat housing with an infrared thermometer. As a guide the inbound hose to the heater core should be too hot to hold at full temp.

 

Check the blower motor resistor.

 

Can I change my response....please? After re-reading this:
If in fact, the engine is running cooler than normal, a blower motor resistor is unlikely the issue.

 

I have had terrible luck with thermostats the last few years in my Tahoe. Always sticking open like yours seems to be doing. I have tried a couple of parts store brands and they work ok for a year or so. I actually bought a new one from the dealer this week and plan on changing it over the weekend.

Only thing else I can think of is the cooling fans being stuck on for some reason but you would hear it. This time of year up in your area the fan should probably never come on.

Do you know for sure that the engine is running cool ? Not sure if a scanner will show it on OBD1 An infrared temp gun should.

 

Are you running straight antifreeze?

 

A scanner will show engine temp on a 93 gm car. Doesn’t matter if fans are stuck on, thermostat controls minimum engine operating temp. If it isn’t fully warming up than the thermostat isn’t functioning properly or you have an air lock. I vaguely remember some cars with the pressurized coolant bottle having this airlock issue and IIRC they have a bleed bleed screw on the engine somewhere. On those, crack the bleed screw when warm until it pees coolant then top it off again once it cools.

 

You mentioned that the blend doors are functioning properly. Why do you say this? I had a blend door go bad on my 96 Oldsmobile 98 and I could only get frigid outside air from the vents even with the heat turned all the way up.