Help an old man out. I have searched this forum and on the net and cannot find an answer. My 1983 F250 has the 7.5 460 carb. engine in it,
What fuel range is recommended for this truck, I will be pulling my 5th wheel and would like to know this before I take off for AZ.
I am still on the fuel thhat was in the tank when I bought it. I'm guessing Mid range.

 

It was rated from the factory to run regular 87. That's when it's all original and tuned like the factory had it. Lots of little things if they are changed might make a difference in this. Is it completely stock?

 

Thanks!!!
Stock as a stove with newly rebuilt carburetor. Runs great,

 

The factory sets the timing a little conservative, and the compression ratio is low enough, that 87 should work, and save you some money also.

 

Regular will be fine, I'd avoid ethanol if at all possible. It's not kind to low pressure rubber fuel lines and parts seen on carbed vehicles and it will lower your mpg.

 

I have a 86 300 and get 11.9mpg on 87 ethanol and 13.7 on 87 non ethanol.

 

You are correct about the ethanol on all accounts. But when you are on a trip, it's hard to find non-ethanol fuel. I am surprised the tree huggers still let them sell it.

That's why all these trucks with carbs should have them rebuilt. The newer kits I am told have the upgraded rubber parts to withstand the alcohol in the fuel. It is hard on them.

 

Your vehicle was designed to be able to operate using 87 octane. As vehicles age, sometimes sufficient carbon builds up in the combustion chamber which in turn acts to increase the compression by decreasing combustion chamber volume. As a result, pinging might be noticed and your engine would benefit from using 89 octane. Some people will retard the timing which will stop the pinging, but gas mileage and performance will be adversely affected.

I was taught to make sure the engine is tuned well and then run as low octane as possible without pinging.

Some will say that they get better gas mileage with premium fuel [93+ octane] or that they "know" the engine runs better. Think of it this way... the higher the octane, the more resistant the fuel is to ignition. A high compression engine [>10:1 by today's standards] needs a fuel which does not ignite prematurely as the piston comes up on the compression stroke, so premium fuel resists firing until the conditions are right [high compression = more heat]. On the other hand, a low compression engine [like my 1986 4.9L; maybe 8.4:1 compression ratio] needs a fuel which does not require so much temperature. If 93/94 octane fuel is used in an older low compression engine, it may actualy require more revolutions before it will "fire up" and most likely will pollute to a greater extent due to incomplete burning since it does not get to sufficient combustion temperatures.

The above scenerio changes with more modern computer controlled vehicles. With knock sensors, the engine control system is capable of sensing how much ignition advance can be tolerated and adjust the timing to just prior to preignition. One can operate a vehicle which specifies the use of premium fuel on 87 octane without damaging the engine, but the computer will significantly retard the timing with the resulting decrease in power and gas mileage.

I hope some of this helps.

 

Update:
Made the move to Chloride AZ on Sat June 1. Had no trouble until I hit ile marker 9 in AZ. Truck Over heated in the 106 degree heat/ not bad, but I shut her down and waited an hour. Got about 12 more miles to a rest area and she was hot again. waited another hour and she cooled down and I replaced lost coolant, Made it all the way to 93and I-40 and she heated again. Cooled her down at the stop light at the exit onto 93 and made it to Golden Valley RV Park 5.5 miles from I-40 and 93, then it cooled down on its own. STUCK THERMOSTAT!!!!
Other than that, and she never got to max heat on the guage, there were no problems. Pulled into Chloride on Monday morning June 3rd after spending two nights in the RV park. Nice place.
Choke was found to be sticking open as well. Don't know if that had any effect on the overheating, but fixed that at the same time I replaced the Thermostat with a 195 degree fail safe one.

 

Ahhh, so that's where all my fuel economy is going. We don't have ethanol-free fuel around here.

 

Around here in Texas I haven't seen an ethanol-free station so far. I think OK has some but that's a long way to drive for gas that may give me 1-2mpg. As nice as it'd be to run it. lol

Here I usually see 10% mixes, which isn't terrible since the factory manual says they'll run up to 15%.

 

Clyde is tuned to run on 87 octane regular, does not like ethanol very much but handles it, and when we get into some Rocky Mountain elevation and the base octane rating drops to 85 runs just fine on that. Whenever possible (KS IIRC) I buy the ethanol free and pick up a little mileage. I can buy ethanol free in MN and WI but the additional cost usually out weighs the mileage or performance gain.

One of the best things I did for performance was to install a Ford Racing timing chain set "straight up" and for cooling I added a second 24 plate tranny cooler in series with the stock 27 plate and then routing into the radiator before going back to the C6. In the past I had 'over cooled' C6's die so this prevents that, but the pre cooling really seems to make an engine temp difference .... that and replacing the dirt/bug clogged 3 core radiator with a 4 core unit.