Fuel Milage...good or bad...

[freebird01]

Ok I took my first long trip with the truck...

Went from southern PA to NJ then to Central NC and back...

With an appx 3,000lb 16' 10,000gvw mid atlantic equipment trailer...a 2500-3000lb suzuki samurai...appx 500lbs of spare parts....appx 500-700lbs of camping gear and 3 adults (600lbs total) so thats appx 8,000lbs loaded

we pulled at an average of 60-65mph in 4th gear the whole way and id say we averaged 10-11mpg truck now has 92,000 miles on it. was using a mix of gas a 2cyl oil in the beginning and ran out of 2cyl oil on the way down so the rest of the trip was on straight diesel. unloaded the truck averages 15-16mpg...

we ran an average of 600-750 EGT's with it climbing to around 950-1000 when really worked up some of the hills but that was only maybe 2 or 3 times in the whole 1000+ mile trip for a short duration we ran an average of 2800-3000 rpms due to running in 4th gear

88 ext cab F250 8' bed 4x4 ZF5 speed 7.3L with banks wastegated sidewinder turbo kit and a fiberglass cap

any thoughts? is this normal?

 

[Full Monte]

Sounds like the right mpg ballpark to me.

 

[Petri317]

My truck gets about 10 mpg empty at 65mph. See sig for specs. Is this reasonable for the transmission, 4:10's, and tires (which are actually 32" tall) Would going to skinnier tires help at all? A freer exhaust and matching new injectors are on the way. (The IP is remanned, and seems to work fine, but the injectors are B and BBs, some look original, some look newer.) What can I do for better mileage? I've heard of people getting 15mpg with c6/4:10 combos. I just want a little more power and a little better mileage. I had a 4:10 truck with a T19 that got at least 13. I love the truck, but this is frustrating. I don't feel like spending tons of money to prep it for a turbo (Head gaskets, studs, valvetrain) and then the money for a turbo. Any suggestions would help.

 

[freebird01]

what im wondering more is if 4.10's would help my loaded mileage at all since i got the ZF5spd with OD

 

[Cheaper Jeeper]

what im wondering more is if 4.10's would help my loaded mileage at all since i got the ZF5spd with OD

Might, if your in hill/mountain territory - since you wouldn't have to keep your foot in it quite as hard pulling hills - though you'd probably be topping them at a little lower speed.

If you're running mostly flat ground, then the 4.10s probably wouldn't help your mileage at all - more likely hurt it.

My truck gets around averaged between 15 and 16 on the last tank - about 40% of the miles I was towning my Jeep (about 4500 pounds with the tow dolly) and 60% of the miles were running empty. Last time I was fully loaded (Jeep + camper + camping gear + 3 passengers ~ 6500 lbs) I got pretty much an even consistent 12 going up & down the mountains around here.

So your mileage sounds pretty consistent to me.

 

[LCAM-01XA]

For what it's worth - my dually, empty, cruising at 1800rpms steady, on mostly level road, gets about 17-18mpg, depending on headwind. I have a non-turbo 7.3 engine, IP advanced about 8 degrees and turned one flat up, "soup bowl" removed, air intake opened up and directed for sucking air from above the PS pump, and straight-piped 2.5" exhaust exiting behind the right rear wheels. Truck has a tall 3-step fiberglass cap that creates some massive aerodynamic drag tho, and until last week the bumper was royally messed up too.

About tires - I have regular 235/85-16 tires with "E" load rating in the front and "D" load rating in the rear, but my spare wheel has a 7.5x16 "highway rib" tire on it, which looks like it will have some great rolling qualities - maybe these "highway rib" type tires will be the ticket for better fuel economy?

 

[Diesel JD]

Petri, I think your best bet is to ditch that C6 in favor of a T19 or ZF5. I used to have that combo, and the usual fuel economy was in the 12-13mpg range, no matter what I was doing. I ditched the 4.10s in favor of 3.55s, and now I get about 11-14 in town(almost no change from the 4.10s) about 12-14 towing, highway and 15-17 empty on the highway. There were a couple times when I supposedly got in the 17-18 range with the 4.10s and C6 but since they were such isolated incidents, I now wonder if there was a mathematical mistake on my part or if the selector valve was letting the pumps suck from both tanks at times. I'm comfortable saying with a C6 and 3.55s I can reliably get 12-13mpg in town on B100 biodiesel, maybe a hair better on dino, on the highway at least 14.5-15 empty at 65mph, often closer to 16-17. It also sounds like your fuel system is a bit cobbled together, you have a reman IP with some original injs and some new ones. You want to at least pop test all the injectors and see where you are, you'll probably want all new BBs in there. Also it should be timed to 1.5-2* ATDC with the luminosity method or 8.5* BTDC by the pulse method. I plan to ditch my C6 as soon as I have some money. I have the parts for a T19 swap, I realize it won't net me much better fuel economy but I hope to pick up an MPG or two, plus never have to worry about that silly VRV again.

 

[Petri317]

Thanks, JD. I have new injectors that I'm waiting to put in, and I'm thinking of getting a new IP as well (don't know when it was remaned; all of this work was done by the original owner, I'm the 3rd.) My truck periodically will stall, or get real low in the rpms after letting off the accelerator pedal when backing up. The pump may be on it's way out. It looks like the pump has been moved so that is advanced as it can get (all the way to the passenger side) but the engine is fairly quiet and I get no smoke even when flooring it under load. When I replace all of this, I'll time it. I've got a buddy with the equipment.

Having had a T19 truck (though with 4:10's), you may grab a couple mpgs, depending on driving style. I like the control of having a manual, but the 3rd to 4th gear spacing sucks, as does the lack of a overdrive. (You may not have such a problem with lack of overdrive with 3:55's.) If I am lucky enough to find a good zf5, I may do the swap, but otherwise, new fuel system it is and we'll see. Hopefully, I can go from 10mpg to the 12-14 range. Even that little bit will make a difference.

 

[Diesel JD]

Oh heck yeah! It will make a difference. The F250 is my DD and it usually is driven in areas where the speed limit is 40-45, maybe 50mph, and not a lot of miles every day, so a couple more MPGs would be great, but fuel efficiency isn't my #1 concern due to burning cheaper homebrewed biodiesel and not driving a whole heck of a lot of miles. I've heard about this gap between 3-4 but I still think probably I can be in 4th most of the time, if I have problems or I start driving long distances I will plunk down the big bucks for a US Gear or GV unit. I'm so in debt now, I can't think about it at the moment.

 

[FordGuy100]

Oh heck yeah! It will make a difference. The F250 is my DD and it usually is driven in areas where the speed limit is 40-45, maybe 50mph, and not a lot of miles every day, so a couple more MPGs would be great, but fuel efficiency isn't my #1 concern due to burning cheaper homebrewed biodiesel and not driving a whole heck of a lot of miles. I've heard about this gap between 3-4 but I still think probably I can be in 4th most of the time, if I have problems or I start driving long distances I will plunk down the big bucks for a US Gear or GV unit. I'm so in debt now, I can't think about it at the moment.

Yeah, the 3-4 gear is big, especially when towing. 4th gear is pretty versitile though, I can go from 25mph (almost lugging it, if you go WOT it is lugging it, but just going through town its not) to 90mph, thats a big range. I think its awsome my truck can run around in 4th at 30mph or a little less, at right at 1000rpm's or less , gotta love the low end torque of these things .

 

[Diesel JD]

So when do you need to shift from 3-4 RPM wise(or speed wise with 3.54/55)?

 

[FordGuy100]

So when do you need to shift from 3-4 RPM wise(or speed wise with 3.54/55)?

Kinda depends on the situation. If I'm just going throgh town, I'll shift into 4th at 30mph. When I'm trying to accelerate fast, or tow up a grade or what not, I'll shift into 4th at 55mph, which is about 3100rpm's or there abouts. It really depends. Usually I will shift into 4th on average, I would say around 45mph, or around 2400rpm's. I'll have to watch what I do tommorow. When your going up a hill, accelerating, that 3rd to 4th kinda kills the power, it falls on its face for a second or two before you build your boost up again.

 

[Diesel JD]

Yeah, definitely going to want that US Gear type deal eventually, right now I couldn't even scrape together $300 if I could find one that cheap. I could almost stay in 3rd all the time where I drive but I'd probably do like you do and shift to 4th as soon as I got to the 35-40 mph range, wouldn't stall it doing that would I? We'll assume not towing or hauling anything too big, and its real flat here compared to Oregon.

 

[FordGuy100]

Yeah, definitely going to want that US Gear type deal eventually, right now I couldn't even scrape together $300 if I could find one that cheap. I could almost stay in 3rd all the time where I drive but I'd probably do like you do and shift to 4th as soon as I got to the 35-40 mph range, wouldn't stall it doing that would I? We'll assume not towing or hauling anything too big, and its real flat here compared to Oregon.

No, trust me, on accident I've gone down to 20mph in 4th, it just lugged it. I've never stalled this thing. I can put it in 2nd, dump the clutch, and it'll buck and lugg some but it'll go, just to much torque and intertia to kill one of these things (though if you were to dump the clutch in 4th doing 5mph I could see it happening).

 

[Petri317]

3-4 gap aside, the t19 is a great transmission. Solid, reliable, easy to rebuild, can be shifted without the clutch fairly easily if needed (learned not to route the clutch fluid line next to the exhaust manifold) I've had it in 4th gear going 25 in my old T19/4:10 truck. I have a 1989 ZF5, but it's got a cracked bellhousing and is missing the shifter parts. It would need a lot to put it back in service.