As to the original post. If you can see that difference when your thermostat opens, it is quote likely that you are okay. The gauge is not absolute. My temp gauge runs at the bar before the N in NORMAL and I run a 160° thermostat. In the south, pulling a 26' gooseneck you need all the help you can get. I can see when the stat opens and as I am getting 12 mpg pretty regularly in the 460, I am happy. Is the heater hot? Are the heater hoses to the firewall hot to the touch? I understand the need for the best MPG possible with the price of fuel. What kind of mileage are you getting? Is there some reason you feel like the mileage has deteriorated?
Tex

 

The electric temp gauge sending unit location:
Looking at the motor from the front bumper. Notice the location of the distributer. Imagine you are looking at the distributor from straight above it. (view from the top). The temp gauge sending unit is about 3 inches from center of dist. cap at the 2 o'clock position. It has one wire leading to it with a small 90 degree boot over the connector.
The coolant temp sensor IS separate/differant and is a taller "tree type" affair to the left of the distributor about 8" at about 9:30 position.

 

Last time I checked, I was getting 12 mpg, which I guess isn't too bad for an F-250 351. Of course that was before I had a new, much less restrictive exhaust put on, and I've had a few other things done to it, too, but it actually seems like I have to fill the truck up more often now than before. I'm sure there are other reasons for the crappy mileage (like the 3.55 gears), but right now I'm looking for anything I can do to improve mileage until I can afford more expensive changes.........

 

Trying to get better mileage I've found that a low restriction cat-back exhaust system does NOT help at all. The major impediment to free flowing exhaust are the catylitic converters. Low restriction converters are NOT cost effective either. Low restriction air filter systems (read K&N FIPK) will NOT do anything to help improve mileage.
Have the engine tuned to an optimum condition, plugs with less than 30K on them, plug wires in good shape, ignition coil with less than 50K, and good dist. cap with a decent rotor.
The VERY best way to improve the gas mileage is to use 4 tires that have a highway type tread pattern in an effort to decrease rolling resistance. Aggressive, heavy lugged tread patterns have a HIGH rolling resistance (like snow tires).

With highway tires, engine tuned properly and my 302 4x4 5 spd stick in a stock condition I got a carefully measured 17.2 mpg on the highway at 59mph.
I added a K&N FIPK system, a Summit Racing Low Restriction dual cat-back exhaust and new shocks all 'round. Removed the belt driven radiator fan and installed an electric fan from a Crown Vic Police car and put on a fresh coat of wax.
Tested for gas mileage again in approximately the same weather, over the same highway, at 59mph, using the same brand of gas from the same pump and measured 17.2. Mildly dissapointed as it showed no mileage improvement.
A week later I had heavy lugged, winter type tires mounted on my other 4 wheels. With the winter tires on I drove the same test circuit under the same conditions as the first 2 tests and measured 15.1 mpg.

So as far as making expensive changes in an effort to improve mileage--- SAVE your money. Nothing will help until catylitic converters are eliminated and the manufacturers can reset valve timing and the ECM's for maximum fuel mileage. And we are pretty sure that is not going to happen.

 

[QUOTE=wcmo sae] I'm sure there are other reasons for the crappy mileage ( QUOTE]

Another way to improve your fuel mileage. Take off your mud flaps and running boards. I speak from experience.

 

Fuel Milage? LOL. Crockpot man you are funny. Doing a careful 59 MPH...you got 17MPG? lol. If you are that worried about your gas milage buy a saturn or a civic. I don't really care personally. I certainly don't go out and try to calculate wind speeds and aerodynamacy of my p/u. But you are right in a way saying that cats do nothing for milage. They don't. They muffle sound and support emissions.

 

Not that I'm "worried" about gas mileage it's just that keeping tabs on mileage is an indicator of the general state of health of the engine and the peripherals. I also installed a vacuum gauge for even a more immediate indicator of actually what is going on under the bonnet.
If I were "concerned" about getting high gas mileage I wouldn't own a full size 4wd p/u that is able to haul around my camper when I'm on a hunting trip.
I set the cruise control at 59 and I leave early enough to get where I want to go in plenty of time. If I had a small v8 that got less than 16 mpg I would say there was something wrong either mechanically or with my driving habits.
If everyone would do their best to acheive maximum mileage with their vehicle then, maybe, we wouldn't have to import so much crude from the arabs.

 

You get 16mpg thru your 302? That's wack. You must drive like an old man. lol. Kidding. No that's cool for you. But my headers are being installed right now and when I get the truck back I am going to want to open it up. Which means...tears....bad gas milage.... not too worried. Do you ever come onto your truck to burn the carbon out??

 

Putting mudflaps and running boards on your truck doesn't change your milage at all. Of the 5 trucks my dad has had in the last 40 years, he has never lost any mpg by adding mudflaps or running boards. On his 88 F150 he put on running boards that doubled as mudflaps for the front tires and added some nice metal ones for the rear. His mpg held constant and if I remember right, with the tires inflated properly it actually went up.

 

wcmo,
Did we actually address your concern that your engine was running too cold? Have you gotten anywhere with a diagnosis? Just checking.
Tex

 

I was impressed with my Bronco's gas milage. Ive owned numerous V8s and none have been as good as the Bronco.

 

Crockpot

I am curious about your experience with better mileage without mudflaps and running boards. I am doubtful.