First step - are you sure the valve is actuating properly? What if the cable to the valve is broken and it's in the open position?

 

^^^^^ never saw THAT coming..... ^^^^^

GREAT advice Van !

but what about the overheating issues ?

 

I don't have many bugs in this area so I don't think that is the problem. My reservoir went from "maximum" to completely empty on one 5 minute drive, so it appears that I have a massive leak somewhere. I don't see a drop of coolant anywhere though so I need to do a pressure test I guess to find the leak? I have responded to your possible causes below:

1- switch for radiator fan not turning on early and holding. the fans both come on at the same time with the temp gauge needle pointing about 12 o'clock. My memory tells me that this has historically been where the radiators have kicked in. It holds until temp drops to below 12 then turns off. I suspect that it would immediately get hot again since the coolant had unbeknownst to me at the time, leaked from the system.
2- failing head gasket ( is the car exhaust smoking white or smelling sweet ? ) No smoking or smell is present and oil appears clean.
3- water pump failing ( are there any leaks @ the pump ?) There are no apparent leaks near the water pump.
4- t-stat not functioning correctly. The fans appear to come on at the correct temp so I assume the t-stat is functioning?
5- both radiator fans coming on in synch and staying on long enough
6- plugged or corroded radiator internally. not sure about this.
7- radiator for the heater, more commonly called a heater core, is plugged with aluminum flakes, as well as the coolant passages, due to 'stray voltage promoted galvanic corrosion'. Comes about due to voltage collecting in long term coolant which hasn't been changed often enough. I saw a core plugged so badly with aluminum flakes, not even a trickle was getting thru. Those flakes all got there due to erosion of passageways promoted by stray voltage and old coolant eating away internally. Not sure about this either. I suppose after I find and fix the leak, if I still have issues I will have to investigate the potential for the heater core and radiators being clogged?

Many thanks again

 

I just wanted to close the loop on this one. It turns out that Van was correct - when set to full cold the HC valve actuator still had about .5cm to go until it was fully closed. amazing that the valve being open that tiny bit could produce so much heat! wow. The wire had come free of the clip so it wasn't functioning properly. Anyway, I reattached the sheath/wire, made sure the valve was closed fully and all heat blowing has ceased. As for running hot, I bled the cooling system several times and finally all was well with the temperature.
thx again for all of your help.

 

Glad you fixed it!