Transmissions/gear splitters/fuel economy

I have a 1995 Ford F 350 power stroke manual 4 speed with overdrive. I bought this truck 7 years ago it had 135k miles on it now has 160k miles. For the next 6 years I plan on using it to travel the west ( home base Portland OR)visiting all the national parks with my son; camper on board and fishing boat in tow. The truck currently gets about 10-12 miles a gallon full, empty, uphill, downhill. I travel at 65 mph at about 2850 rpm my question is how to increase gas mileage around the 20 mi range, gear splitter, or new tanny and front differential best way to get there. I am installing a better exhaust system now. The tires are 35/8.


I am not familiar with 35/8 tires. The truck was originally equipped with 85 series 16 inch diameter load range D tires. If the 35/8 tires are significantly larger in diameter your actual miles traveled will be greater than what is indicated on the odometer.

You want to nearly double the MPGs, that’s just not feasible.
My neighbor’s Sport-Trak doesn’t get 20 MPG highway, and that’s just an Explorer with a tiny pickup bed.

No way to get much of a mpg improvement with that rig. Just keep it in top tune, with good radial tires inflated to the appropriate psi.

4th gear is OD? Or 4th is 1:1 and you have 5th gear OD?

My Trailblazer is a 6 cyl with OD. It’s not as heavy but still only get 18mpg. I think you’re being a bit unrealistic. Especially with a camper and boat in tow.

@dalypdx - what’s the gross weight of your truck+camper+trailer+boat? 10,000?

The engine speed is rather high. With 3:54 gears it should be about 1800 RPM, with 4:10 gears about 2100-2200 @ 65 MPH. Is 5TH gear (overdrive) working? With different gearing you should be able to get 16+ MPG empty and 10-12 MPG loaded.

F-350 Super-duty 4WD (he mentioned front diff) with a camper and towing a boat. Dude, I think you’re asking too much. On some Power Stroke forums, I’ve heard of guys getting to 18 and 20 mpg with this rigs, but only by 1) keeping the speed down to like 60 MPH, and 2) driving empty, no load, no trailer.

They did have some tips, like engine and exhaust mods to help the engine breathe better and using highway gearing to bring the engine RPMs down, but you need to match gearing in the front and rear diff, that’s VERY IMPORTANT. The RPMs at 2850 at 65 MPH sounds like it is loaded with 4.10 gears, which is great for low speed stump pulling, large trailer hauling, and off-road mud slinging, but horrible for highway. The 3.55 gears are much better for highway.

I’d think with a diesel of this size in a pickup, you’d want to run around 1,700-1,800 at 65 MPH. 2,850 RPM at 65 MPH sounds awful high. I think in 1995 the Powerstroke engine was still a re-badged Navistar T444E engine.

Years ago, one of the car magazines tried to get more fuel economy from a Chevy Suburban. I think they got about .9 mpg more. They made this air dam and put it under the radiator and it was good for .4 MPG.

This info is going about as far upward as your fuel economy. It won’t help much.

Based on the RPMs and assuming no clutch slippage, my vote is with BustedKnucles about the truck having 4;10 gears in it.
That should be easy enough to determine.

Every has just about covered it here. The PSD gets MUCHO better mileage below 2000 rpms, but than you are carrying a slide-in camper (5K) and dragging a boat (3K). Ain’t gonna happen in the current truck/engine combo you have. You have lots more weight and a TALL camper to contend with.
@doubleclutch: All the diesel engines in Ford pickups were sourced from International from 1983 until 2010. Starting with 2011 models the trucks are outfitted with a Ford brand diesel, designed and built in-house. Remember, Ford is a Motor Company.

You want to take a 12 mpg truck, add a camper and tow a boat and get 20 mpg. I want to be 17 again and have a million dollars.
I would say our chances are about equal.

I’d settle for 27 and a half mil, but figure the odds.