96 F150, 302 4x4 E4od truck. Truck was running hot and temp was rising and falling for a wile. when it stopped falling I replaced the thermostat with a 180 degree stant brand. fixed the hot running but it wouldn't heat up into normal range so I replaced it with a 195 degree stant brand. It still won't heat into normal range. I also replaced the water neck and this one has a rubber gasket rather than the Film type that was original.
So what I think may be happening:
1. There is something I simply dont understand about the engine cooling system
2. Both 180 and 195 degree thermostats are too cool for a 302.
3. the rubber gasket on the New after market water neck is not compressing fully and coolant is constantly flowing around the metal ring housing of the thermostat.
BTW, when I pulled the 180 degree thermostat out it was not stuck open.
Anyone got any ideas?
Thanks in advance for your input!
Best,
Phil

 

Maybe your gauge is reading wrong? Install a different gauge, use an infrared thermometer to see what the temps actually are.

 

195* is correct.
Point an IR gun at the waterneck and check.

If your aftermarket water neck is allowing coolant to pass around the thermostat it may never heat up.

If you overheated the truck maybe you should replace the temp sender.
They're only full of wax anyway.

 

Yup, I am thinking it is the temp sender also now. It was running hot for a while and it is 20 years old.