My 92 F150 (5.0) 2wd E4OD never seems to get hot. And I suppose that is a good thing. But, I'm wondering if it is running too cool. I just drove about 40 miles on the highway at 75 MPH. It is 90+ degrees today. But, the temp never reached the middle of the gauge. In fact, I don't think it has ever gotten to the middle and certainly not past the middle. Last summer in July I towed a 2000 lb trailer with a 3800 pound car on it for 240 miles. It was 105 degrees or hottter the whole trip. AND it never went past the middle. Maybe the gauge isn't super accurate. But, I'm including a picture.




This picture raises two issues.

1. How the heck did my cluster get so freaking dirty? Can I take it off and clean all that out?
2. It is not even to the R in Normal. Is it running too cool. I'm guess that would be a bad thermostat. That might explain the lack of heat during the winter.

 

1. It could be your coolant temp sensor getting weak. It is a resistor type meaning the resistance changes with temperature. Thus causes the gauge to deflect accordingly.

I have changed mine and got higher readings with new sensors. My new high reading is now on the "M" in NORMAL

2. Does it take a long time to warm up? ​​​​It could be the thermostat stuck partially open.

And it's not hard to remove the instrument gauge cover and clean it. While you have it apart replace the instrument dash light with LED's

 

That looks like it is reading where all these trucks seem too. I say it is normal.

 

my 94 (5.8) has been a daily driver for over 5 years now and i don't think it has ever moved past the "n".
i have never been overly impressed with the heater output on this truck (my 87 chrysler minivan could give you heat stroke if you left it on full heat for too long) but if it doesn't heat up the cab reasonably well in winter it may be time for a flush.

 

I'd say you have a bad thermostat, but the OP's is probably fine.

 

It's always important for any engine to reach the NOT (normal operating temperature) as quickly as practicable even in the tropics, and achieve the design temperature that the engineers want. If you've ever torn an engine down that was ran without a thermostat, or a defective thermostat, too cool, it is absolutely sludge city. The 160° F thermostats were designed for use when methanol was used as antifreeze, before glycol coolant came into wide use.

Engine (cylinder) wear is reduced dramatically, fuel economy maximized, pollution minimized, and the oil temperature (this always lags coolant temperature by quite a bit) reaches a level that effectively boils off condensation and acids. Most everything for decades now, and on the road today, has a 195° F thermostat from the factory. My 1964 operator's says "185-195 degree thermostats usually provide better fuel economy"; 195 degree stats aren't new.

The rated temperature of a stat is roughly the minimum temperature at which the engine will be maintained, not the maximum. Thermostat will start to open (and just as important close at this temperature) Thermostat will be fully open somewhere around 210° F; note too modern computer controlled engines will remain in a "closed loop" engine warmup mode if an incorrectly rated (or defective) thermostat is installed and waste fuel and foul plugs. And your heater won't work worth a dang.

With all that said the gauges on most vehicles are only slightly better than useless. You can use one of those laser pointer thermometers. I'd be inclined to simply replace the thermostat when changing out the coolant. It's getting up there in age and may be getting weak. Use a genuine Motorcraft replacement part here, with the exact same temperature rating specified in the shop manual. Resist the urge to try and outhink the engineers here.

 

I have that gauge, and with a 195-degree thermostat, that is precisely where the needle sits, and yes, it does move a bit on a long upgrade at freeway speed.