OK, fellas. I did the search routine but my search-fu is not with me tonight.

I am interested in the real world MPG differences between the C6 and E4OD trucks. I know the mechanical differences in the two, and I think the E4OD gets better MPG due to the 4 + over and locking TC but I want to hear from real owners. Yes, the rear-end make a difference. I am looking for or to swap out to 3.55s when I buy a truck. I won't be towing more than 5K lbs in the immediate future.

I am planning a 4000+ mile trip from TX to MA and back. Fuel is a big concern and I want to be prepared for what to expect on each platform. I am still in the market for a good IDI. Things here in DFW seem to be slow on the sales side. I am planning this trip for July/Aug but no date is set yet. I would like to get a truck in the next month or two so I can have time to make it reliable enough for the trip.

On the highway, I would be thrilled to get 20 or more MPG. I am also considering trucks with the factory trubos.

Anyone with a ZF4 or ZF5, post your highway mileage as well. I am not stuck on an auto but it is easier for me to drive. I would trade some MPG for convenience, though.

 

The best i've ever seen out of my 1990 4x4 F250 7.3 5 speed 4.10 gears is 17-18mpg back when it was new (still had the stock 235/85 tires) (I have kepted all my mpg ratings in a log book and still have all of 'em today). That's driving at a steady speed of 60mph (no cruise control), 95% highway driving.

It now has 377k miles and last time I calculated mpg it was getting around 13-14 mpg same conditions with 265/75 tires. (needs injectors and IP).


My 1987 6.9 Class C motorhome, C6 3.54 gears gets 11-12mpg, has excellent tune up, and timed. 215/85 tires, dually, 11,000 pounds, big wind load, cruise control @ 60mpg.




And you mean T19 4 speed, no ZF4.

 

John,

E4OD on the 1990 and up, right?

Yeah, that ole' motor home you got sure does skew the results! It would be cool to have one of those, though. I could probably save so much money in rent if I had one. I am surprised yours in such good condition being that it is in Canada with all the road salt, etc. Keep her running.

It looks so far that 20 MPG would not be out of the question for and IDI that is up to par. Yeah, T19. I guess I was thinking ZF5 and ZF6 but the 6 is not on the IDI. I plan to keep whatever i buy as stock as I can unless it really behooves me to upgrade a part.

 

definitely a differnent story with me!! haha. When i keep to my game plan i do very well.

1989 7.3 with C6 and 4.10's. Running empty with my old pump and new injectors i would fetch an average of 14mpg's.

Now with new pump and gresh gp's and new controller and my very new injectors i get nearly 18mpg average. My last tank gave me 16.9mpg because i cant keep my foot out of it haha. Its timed to 8.5btdc. Its running like a beast. My intake is custom, my exhaust is custom. Its a custom result for a C6 as anyone will tell you. When i can romp on it off each light and still grap 17 almost, yeah im zeroed in to where i want to be!

 

My 1990 F250 has the ZF5.

The E4OD came out in mid year 1989.

My motorhome has never seen winter in it's whole life! In fact, I use to store it inside, in a barn on a farm that a guy rented to store campers. It's only been stored outside for the past 3 years now. I tarp it, only half way down the sides so the air circulates around to prevent rust and rot. It's also back up on a tarp on the ground to prevent the humidity comming out of the ground getting to it.

 

truck in my signature, just the truck with nothing in the bed, on summer fuel, would run 20 mpg on the interstate at 57-58 mph. Same truck loaded with like 3000 lbs of camper, under same road conditions, mainatined about 15 mpg.

 

i have two trucks, one with an E40D and 4.10's i get about 14 and drive like a grandma. i have one 5-speed with 3.55's and get 19 still driving like a grandma. right now i am taking the 5-speed out and replacing the E4OD. I do not think you will get 20+ unless you put in a spliter. as far as the IDI goes it is very reliable. you said you are not towing much you good for 3.08 gears and save there.

 

He can hit 20 without a double overdrive, and if he gets a reg cab 2wd truck with 3.55s it will make it that much easier. Now a crew-cab dually with 4.10s won't get there, but a lighter truck just may...

 

I got roughly 4 MPG inprovement when I tossed the C6 and installed my current E4OD. It depends on the conditions though. Usually I averaged 16 MPG @ 70 MPH with the C6. Towing it was 13 MPG w/C6 and 15~16 under the same conditions w/the E4.

Usually I can stay around 20 MPG on summer fuel if the truck is empty. Now if I can cruise bone empty without a canopy at 55 MPH or less, 24 MPG is consistently within reach (though I suspect many other IDIs could do that without having to spin as slow as 1200 RPM).

One problem with having an extra gear is you might find yourself tempted to keep up with and eventually leave behind the rest of traffic.

Don't expect an E4OD to break even in cost anytime soon unless you spend a lot of time on the highway though.

 

My fairly fresh rebuilt 1984 F-250, T-18 4 speed 4x4, nothing in the bed just running itself down the road @ 65 mph, 4.10 ratio. Its running 19 on the highway @ 65, if i go 60 mph it will be around 21 and dont use the go pedal to pass idiots or semis.

My dad's 86 6.9 w/C6 3.55 ratio (just found this out, thought they were 4.10) @ 70 mph will run @ 18 on the highway if he is not using the go pedel on a hill or passing semis, ect. ect. If he does 65 it jumps to 21. I think this is because of 2x4 but idk.

My friend Jared has a 1991 7.3l 4.10 ratio E4OD runs itself down the highway @ 65 mph and can get 21-22 mph if he is careful with the pedal.

 

Maybe i need new ip and injectors, i have never been close to20 with the e4od.

 

lets say the the E40D gets 4 MPG AVG per gallon more over a C6,diesel fuel cost $3.50 per gallon,and you drive 15,000 miles per year.
cost for fuel per year;
C6 @ 14MPG = $3750
E40D @ 18MPG = $2917
savings per year = $833

now lets say the truck you buy with either trans will last for 10 years with proper maintenance and say fuel stays at $3.50 per gallon (yeah right lol.naturally it wont,so as the price of fuel goes up,so does the $ savings.)
your total fuel savings @ 15k miles per year,for a 10 year period @ $3.50 per gallon;
$8,330

so you need to ask yourself,is the 3 speed/direct drive C6 trans of yesteryear which cost less to buy/rebuild,"really" cheaper?
http://www.fueleconomy.gov/feg/savemoney.shtml

 

Great info guys. It looks like 60MPH is the sweet spot for mileage on these trucks.

How hard is it to change the gears?

I would love a Gear Vendors over/under but it costs as much as a truck! I don't think I would make my money back on it.

 

there a few threads on gearing swaps, pretty sure david 85 has the 3.08's and if you are ever rolling around the island of bc nd see a flash it might be him haha. 60mph might be the sweet spot for a e4od but 50 is better for the c6. I can go 60 all day but i see it in the mileage.

 

This is a very interesting thread!