Overheating when "non-working heat" turned on

[wire2power]

My 2000 Ford Taurus overheated the other day. Its fine now. Let me explain, I have no heat, no leaks. That day, I blasted my heat hoping for heat with no luck but thats when car overheated. I let it cool down for hours and ALSO made sure heat was OFF! I drove the car and no problems 1 week later. Last winter, I remember doing the same thing and it overheated. I did NOTHING different other than turn NON-WORKING heat off! What is going on? I put in new thermostat last year.

[shorod]

Welcome to the forum!

So last year you put a new thermostat in. Was that before or after the first no heat/overheating issue? Are you positive that you installed the thermostat correctly? Did the new thermostat have the little jiggle valve that needs to be up?

-Rod

[wire2power]

Rod,
I'm 90% positive. if I did put Tstat in backwards-wouldnt motor overheat often? Like why is it running fine now when in fact I did nothing besides leave the broken heater off? Note that its so cold that I keep hoping for a miracle like heat finally begin working. I'm sure the heater core is shot. Really dont want to spend the money (may be getting newer car soon).
Thanks

I think it was after first over heating issue.

[shorod]

I really have no idea why it seems turning the heater on causes the vehicle to overheat. If the heater core were shot to the point of leaking, you'd be losing coolant and still have a constant overheat issue with the engine, regardless of if the heat is on or not. If the heater core is plugged, then coolant won't be flowing through the core anyway and it would be very much like if the heat was left off.

The only think that would make sense to me is if the radiator cooling fan is not working (which would almost have to be the case anyway for the engine to overheat) and when you turn the heat on, you're actually turning on the defroster or some setting other than "Panel" and the A/C compressor is kicking in and loading the engine. Just about any setting other than Panel will cause the HVAC system to attempt to turn on the A/C compressor. However, depending on the ambient temperature the A/C compressor should attempt to turn on anyway if it's too cold outside. I'd explore the operation of the compressor clutch and the radiator cooling fan a bit more though.

-Rod

[wire2power]

Rod,
Thank you. At this point, I'm gonna just wait and see. As of now its giving me no problem whatsoever. I'm posting another thread regarding travel... If weather or not it would be fine to travel from NY to NJ approximately 350 miles each way highway miles...I easily drive 300-400 miles most weeks in city.