12HT cooling problem

If you have done all the normal checks I would stat to look at the gauge
sender and wiring.(maybe colder air temp may not help wiring ie moist air)

Might be a blocked heater core? Test by seeing if heater outlet temp is warm (fan on low) periodically for the first few minutes after start-up. If the outlet air is cool, then "short-circuiting" the water to the heater core would be the definitive proof by removing the restrictive core. It should then warm up normally. If it doesnt then the problem is elsewhere.

The same sympton can be caused by either a blocked or restricted radiator or a faulty fan clutch.
What happens when the radiator is either blocked externally by mud /debris or internally by corrosion/debris is that the thermostat will sense the increased water temp (your heat spike) and open and because the water isn't as cool as it should be from the radiator it stays wide open to maintain engine temp.
When the cooling system is in good condition the thermostat will 'cycle' opening and closing to varying degrees in response to coolant temperature changes but when the cooling system is partially blocked it has to stay wide open to allow enough coolant through.
In your case as it seems to only happen on first startup I would suspect the radiator/cooling system if there is nothing wrong electrically with the gauge.
Going to the trouble of removing the radiator and having it mechanically cleaned by a radiator place would be far cheaper than an engine rebuild.
Peter

WHEN ITS 20 BELOW C!!!!!!!! WHERE DO YOU LIVE!!!!!

What model car is it in?

Sounds like a dodgey temp guage or sender to me.

My GQ did the same with the temp sender was dead... $40 for a new one (ouch), and its good to go.

Maybe get the radiator checked for blockages, and physically remove the rad and hose it out, turn it upside down and hose from the bottom of the rad so it comes out the filler cap..

Lots of thigns you can spend $100's on this, I know I did :(

Lyndon,

I went through all that drama with my old 12H-T. I am 99% sure that your problem is the same as mine.

The voltage regulator which supplies power to the dashboard temp guage is a primitive bimetallic thing, that gets sticky contacts. Now the trick is that this voltage regulator is located within the fuel gauge and supplies power to both fuel guage and the temp guage (check your wiring diagrams).

Two options - remove the fuel guage from the dash and clean up the regulator contacts (a little tricky) or buy a new fuel guage (which contains the regulator).

I replaced the fuel guage and never had a problem since!

Phil

Lyndon, Agree with Phil. Had the same problem but it occured as I was driving along which was a bit nerve racking as I had to stop each time to make sure that it was that problem and not a blown hose. Auto electrican replaced fuel gauge (or voltage thing) and problem solved.