In my 92' F-350 ( in sig ) the heater gets hot like normal, but the gauge only moves a little between the C and the line where the normal is. When I go up a steep hill or pull something up hill, it will move to the N and O spot but when I level out or go downhill it returns to where it is. This truck has the towing/Camper package and has fresh coolant in it. Is this how the package makes the truck run??

 

Not saying it couldn't be that, but in my experience when a sending unit goes bad, it just opens up so it won't move at all. I also got one once that the resistance wouldn't go past the point of reading 60 degrees but once at 60 it read and transmitted normally with no error. Also in my experience with a 5.0L EFI that had a broken thermostat, the engine temp would get up to about 130-140 degrees which was enough to make warm air. At that point the gauge needle wouldn't even be at the leftmost hash of the "normal" range indicator. Installing a new 195 degree stat got it up to the lower third of the normal range.

 

You could try grounding the sender connector to the block and see if it pins the needle.

 

Dash gauge has it's own sender just behind the #5 injector on the lower intake, I suggest replacing it and be sure not to use too much thread sealer when doing so as it must ground through the intake. Also note that the dash temp gauges typically reads pretty low on these trucks.. often just barely into the normal range at full engine operating temp.

 

I'm pretty sure the thermostat is working fine, water in rad lowers when warming up and heater blows HOT! but not hot where it would be overheating. Would the towing/camper package have something to do with it running on that mark(between C and first notch before normal)? Like I said when going up hill and towing it gets to the normal range, just goes back down when leveling out. Truck doesn't over heat or smell weird or anything. I'm just a worry wart

 

Tow package includes a double row rad if I'm not mistaken and that will overcool a bit in the winter and at particularly cold temps and higher speeds.

 

Did you mean once it warms up? Normally during warm up the radiator level will not move until the thermostat opens.

The thermostat controls the engine's minimum temperature, not the maximum. The radiator should only control the capacity to cool if that makes sense.....if you bolted a radiator the size of a barn door to the front of your truck it shouldn't have an effect on where the needle sits under normal operation if the rest of the cooling system is operating properly. You can hit up any parts store or shop and probably borrow an infrared gun to ping the engine in a few places to see what it's reading and then either decide to correlate your gauge with a known temp, or if it's indeed running cool to change out the thermostat (if not sure of rating) to fix that, or if it's running correct temp to change out the sending unit to see how it affects the gauge.

As an aside, I run a 160 degree stat in my supercharged S10 and my factory gauge does at least have numbers on it (starts at 100). It sits where it's supposed to and the heat is hot, but I know that on the F150 that I fixed, that 160 degree temp would barely register on the gauge.

Not saying one thing is definitely the issue and one thing isn't or anything like that, just throwing out suggestions based on personal experience. You'll get it one way or the other.

 

if the coolant level is dropping once you start it then the thermostat may be stuck open. my 302 was doing that when i had a "fail-safe" thermostat (which, only lasted about 2 months, waste of money). Would be warm, but the gauge would barely move. replaced the T-stat and worked like a charm, even the coldest winter ive ever been in, i was nice and toasty with the gauge right where i like it, almost straight up, but a little to the left. about the...O to R region.

 

I had the exact same thing happening in my F150. The heat was hot, the temp gauge would do the same thing as well. I replaced the temp sensor thinking it too was the problem and nothing changed. So I pulled the thermostat and found it to be stuck open slightly. This caused the truck to run cooler than normal, but still produce good heat from the heater. When I would go up a steep hill or really get on the gas, the temp gauge would rise a bit up to where it normally should be (between the N and O). Now the temp gauge is always between the N and O, but my heat has not gotten any hotter surprisingly.

 

Thanks for all the info. Truck warms up before coolant drops. Ill check and replace the thermostat anyway.

 

Not surprising.
The heater loop bypasses the thermostat entirely.
The slightly open thermostat would make for longer warmups, but once it opened it would not change anything.