Is that downhill the whole way on both those trips? That's the only way that could be possible, that or your numbers are inaccurate. Those numbers unloaded would be a real big stretch, let alone towing. Mine has got a best of 16.87 MPG driving two lane blacktop at 45-55 MPH with no concern for saving fuel. I could see low 20s unloaded if the truck was set of for max MPG and driving it like your life depends on every drop. It's simply not going to happen while towing any appreciable load though.

 

like i said i got the receipts. and a 30ft goosneck on the trip to cordelane isn't unloaded.

Texas to Oregon was 16k gross.

typically i run a average of 22k gross and over 60k miles per year. this has been 1 of my better engines.

and like i mentioned you have 205hp engine, mine is set to 160hp. a farmer i know has the 205 hp. his truck is lighter by 6,000 pounds. and gets 13 mpg going to the fields at most. i take my truck and get 22 mpgs. we ran the miles and fuel usage. same size front tank and on same road and had the same tire size. only difference was engine hp, my rear axle is 4.90 to his 4.10 and i have 1 size smaller injectors. he wasn't to impressed with his idi till then and went and found 2 more idis he bought. Also i know my injection pump has been going out and mileage is down. that 22mpgs would be higher if i get this pump rebuilt.

 

the problem is in your gear ratios to tires size ratios. my bet is because your speedometer is no where reading your actual speed, your MPG is no where near correct either.

 

its really simple math, full tank of fuel, burn the fuel and top off. how much difference = gallons used divided by miles. and at 4.90 rear end, my speedometer is correct. as i have the correct setup. in transfer case. i know also on rpms my speed. which is a simple formula when calculating gear ratios.

 

Wanna bet? https://www.oilburners.net/media/img...18_194706.191/
The 2700-ish peak torque numbers are accurate; the other pulls were in a different gear, so the RPM is off by a fraction of .78
(No, my setup isn't typical. Turbo on there and the ability to burn much more fuel)
So... I already did it and it did work. For 3 years so far.
On my '88 tan truck, down with motor issues(long story). I hauled decently heavy in double overdrive(at 74) for probably 300 miles at a stretch multiple times(Seattle to north of Spokane), as well as shorter trips. Can't stay in double overdrive below about 70 due to the RPMs dropping below where the turbo kicks in(2K rpm) and losing power.

Sounds like a 6.9 IDI with the H.A. calibration. Would run leaner at full throttle, especially at lower altitudes, so you'd get less smoke and better burn characteristics... but less power.

Note - the 6.9 in the fords were either rated at 160 or 170, vs the 7.3 going up to 180, 185 for the 7.3 factory turbo block.

Something's not right there, honestly. Timing(How old is your IP again? Did you get it timed correctly?), or your thermostat is broken.

I mean, I'm running higher RPMs, pushing more fuel(more heat going into the block), and I've only had a couple of times I've had to back off. Last time was last August with a big truck camper on it, pulling a grade on Hwy 395 going towards Oregon... I was going about 70-74 at the time and had to back off cause the water temps started getting into the 220s. Backed down to probably 55-ish MPH till I was past the grade. I'd bet it would have done it OK anyway(220 is *not* the limit as several people have told me), but I didn't want to stress it.

 

i know my toque as its a international made motor, peaks at 1800. anything over and i loose power. especially on grade towing. i will push to 2200 rpms but can only sustain for several minutes as i have said.

I am just repeating what gear vendors and there engineers told me, for my weights and engine they dont recomend there over drive. i asked if anything can be modified and they said no. i would be dealing with bearing and gear failures. i dont beleive them entirly but not worth the $3,000 to find out when theres stronger and better options.


it is a 7.3 stamped on the side of the block at 160hp, not a ford version as i have said. i have a 145hp 7.3 idi i am looking at buying, international also. 185hp and 205 are the fords that are out there but most are 205 hp rated. the biggest difference is the injectors are a size or 2 bigger. different injections pumps also.




its a old engine and most parts are factory and haven't been messed with. the injection pump is on the way out and in 2 years of towing acrosss country, i have lost at least a 1/3rd the power i had.

on 395 towards oregon, i hit the grades at 2200 and drop to 4rth sometimes 3rd, and drop to 1800 to 2200 rpms.

i have 2 gauges both work, 1 front of motor that's factory and a add on in the rear most location that's mechanical and is accurate. a thermostat set to 130 degrees, which is a pain in the winter and nice in the summer.

problem with engine temps is that above 230 degrees and pistons have problems if original as they are aluminum. i know if a block has been rebuilt this isn't a issue. so can run hotter.

next time i am out that way working will try to get a hold of you and can show you what i have. i know at the moment i have different gears 4.10 as my old sterling blew apart, so will be re-gearing this axle back to 4.90 or 5.13 when i get a chance. when my transfer case self destructed i dropped 3mpgs. this one has different gears and is ready blow also ha ha. this zf5 isn't far behind.

 

Interesting discussion!
So you have a ZF5 manual?
But to me it seems you do have a lot of work when you go out for towing? Heavy the 32's tires, light the 37's, I guess that when you change the tires you don't adapt the mile counter (speedometer)?
could that be a reason why earlier on somebody mentioned your speedo was off?
Really, I'm interested in the way you do that, my F-350 only gets a bit better then 14Mpg empty,with a flatbed and with a E4OD at 60-65Miles and abot 2000-2200rpm. and 1:4.10gears 235-85R16 tires. 7.3na 180hp low altitude.

 

32 inch tires speedometer is dead on. 37's i am off slightly. but i know at 1900 to 2000 engine rpm i am at 60 to 65.

the key to these motors is keeping rpms down as with any engine. with my 32 tires i dont go over 2000 rpm unless i have to. and like to be at the 1800 mark. every engine is different. the e40d will take more fuel, thats a given due to energy loss. i know the energy loss going thru a auto is more the a clutch but depends on circumstances. given the chance i would put the 6 +1 trans in or Allison auto in before sticking with a ford trans on these engines.

check you're injector size? i run bb. its stamped on the side. the originals where from England bb and had more power and less fuel then the new replacements i put in there. although the same size there is something different.

aa 85 r16 tire is a 33 to 33.5 tire. on all my fords with 4.10 i drop to a "75" 31 to 32. makes a difference in power and fuel but sacrifices getting there faster.

 

32" tires, 4.10:1 gears, 1900 RPM = 58 MPH
32" tires, 4.10:1 gears, 2000 RPM = 61 MPH

These numbers vs what you mentioned your MPG calculations could be over 6% off in the optimistic direction, assuming the tire height you provided is accurate (did you measure the height?). That would only account for around a 2 MPG difference though, and there's no way that truck is getting 25 MPG pulling a 30' gooseneck, loaded or not. Have you checked speedometer accuracy with a GPS speedometer? Your numbers are off by a significant margin somewhere, I believe the various numbers being off are stacking up to a very large error with your 27 MPG number.

 

like i have mentioned before i have 4.90 gears. with a reduction in transfer case.

like i have said to others, been there and done that. got receipts and logs showing it.

also as i have said fords are diferent then internationals. fords run injectors 1 to 2 times bigger.wwhich equals more fuel usage.

 

Im just gunna jump in here and say nope. We have two 6.9 powered binders with original engines. Both are rated at 170hp per the valve covers. The only substantial difference between the IH version and the ford recieved version are air cleaner, cdr, accessory brackets, exhaust manifolds, oil pan, and the governed speed of the pump. The pickups will free rev to 3600 or so, the IH pumps will free rev to 3300, under load, thats around 3300 for the pickups and 2800 for the IH. The one we drive most commonly is the service truck, its a S1400, with a... wait for it..... a 5 speed, and a 2 speed rearend (which is shot). The truck weighs 19000lbs on average, if you want it to move, you keep it well above 2000 rpm, even by 2k, its starting to bog down, and losing ground fast. It goes down the road at 62mph hard on the governor, everywhere it goes. It does seem to get decent mileage given its weight and how its driven, gets around 11. It runs well too considering the 340k, on what appears to be all original fuel system, but is probably the most cold blooded idi ive yet to be around. As for internals being different, nope. There are a billion different pump calibrations, the bulk of which seem to have no bearing on pump tune. Those are the only differences. Same oil coolers, same cams, same heads, same assortment of injectors. IH and ford both offered high altitude versions, which were nothing more than derated IPs so as to not smoke in higher altitudes. Also, in OD with the converter locked, an E40D is as efficient, if not more so than the ZF.

 

Sorry I thought you had mentioned swapping to 4.10:1 gears at some point. My mistake...

32" tires, 4.90:1 gears,, .76:1 trans, 1900 RPM = 48.6 MPH
32" tires, 4.90:1 gears,, .76:1 trans, 2000 RPM = 51 MPH

With the updated information it looks like your MPH numbers are off by around 20%, suggesting your actual fuel economy would be at most 21 MPG. You have also mentioned a reduction in the transfer case a few times. What ratio is that reduction? I am figuring numbers on direct through the transfer case, not a reduction. Reduction would further reduce calculated MPG as your actual speed would be lower in the RPM range you mentioned.