BLU4TJW

You are correct sir. My 5.0 Screw = 18mpg consistently, mixed driving. Highway numbers, traveling 65-70 mph yields me the same. Anyone who gets better I figure are fortunate enough to drive down hill everywhere. I also have seen 21 mpg on that perfect day... flat, no wind, cruising 55 without a care. Then I drove through town into my drive way and saw 18! If the 5.0 is kept to 50-55-mph I do believe it would see its posted numbers regularly. But those speed limits are completely unrealistic. The truck is far too much fun when you romp it, and have seen 14-15 mph in town driving. That will drop your good highway mileage faster than an Ecoboost owner can say "TORQUE"!

Brad92

Here's my opinion. I have had experience with V6 and V8 trucks, mostly Chevy and Dodge though.

A V6 in a truck doesn't get significantly better fuel economy unless you are content to drive like grandpa. In fact, if you are used to a V8, you will find yourself getting less MPG because you have to rev it to get the same speed. I won't own a V6 in a full size pickup again, unless its an Ecoboost or the like, because the fuel economy is just not there. A smaller engine will have to work harder and use more fuel than a larger engine given the same speed and acceleration.

Again, its just my opinion, so take it as it is.

06screwlariat

I agree, it like how the mustang gt's can achieve awesome highway mpg's, sure it's a V8 but it doesnt have to work as hard as a V6 to keep up.

Belyeujon

Im currently getting 16.9 mpg and i have to drive over a mountain everyday, then i get on the highway.I find that if you want to get good mpg in these things, dont even attempt to go over 70... Ive tried doing this for a solid hour drive down to the lake close to us doing 75 with no stops. resulted in a 18mpg trip, on the way back reset the comp, then came back doing 65-68, got close to 20-21 mpg. over all im happy.

zap

Size doesn't have to do much with it but torque does. If your running peak torque at 2000 rpm, you will have a massively efficient vehicle. That is why I know guys with Common Rail 5.9's that can make between 26 and 30 mpg (stock). I have a few friends with 6.7's (Cummins not PSD) that make about 24-26 mpg after deleting emissions. I have a friend that has a 500 horse LBZ Duramax that makes 25 mpg. All because the engines are running at peak torque going 65 mph and mileage doesn't suffer much to run up to 70 mph. These are all 2WD and 4WD 3/4 ton diesels...and they are getting better mileage than most new trucks no matter what size or fuel your running.

Brad92

I can pretty much guarantee you that a Cummins will not make 26-30 mpg stock. Unless you are talking about a 4BT, which you're not. Even a first generation 5.9 is going to get maybe 24 tops. The 6.7 is not going to make 26 mpg with deletes unless you hypermile.

Diesels are also direct injected and don't have a throttle that restricts airflow like a gas engine does. All light duty pickup diesels have a turbocharger, so displacement doesn't really matter. So, its not even a valid comparison.

A 25 mpg LBZ is semi believable but my guess is that he is looking at the DIC and using those MPG numbers. The LB7 is considered to be the most fuel efficient Duramax and guys making high power numbers still get less than that.

I have worked on my parents 04 Duramax and I have a bunch of friends with Fords and Dodges. I'm not saying that because I want to boast or make myself seem like a master diesel tech, I am throwing that out there because I feel I am more knowledgeable than the average person on a diesel

My argument was that a smaller displacement gas engine will have to use more fuel to accomplish what a larger displacement gas engine can do easier.

2000xl_toronto

The only time my 5.0 sees less than 20mpg is when i drive pretty much the whole tank in-town with red lights at every intersection. I have done 10 fillups since I got it and only one was less than 20mpg. I've had as high as 22.1 in 50/50 driving and up to 24.5 on a 50mph 300 mile road-trip.

Mach 1

Brad..FWIW..the new diesels have throttle plates..With Ford they go back to the 6L from 03...

I do agree with you on the fuel economy of the heavy/super duty trucks, they dont get 25mpg..OEM even with a tune or emissions delete..

I do know of a 7.3 that gets 27mpg, however it is lowered 5 inches has 3:08 gears, skinny tires, rigid spoiler, and other various airflow mods..

But I cant believe a 4X4 with tires up in the air is going to get 25mpg..NO way..

Brad92

Ok, I'll admit you have me there. I forgot about the newer ones having a throttle for emissions reasons.

Personally, I think there are a ton of BS mileage claims all over the internet including this site. IDK if its because of people not hand calculating when modded or what.

zap

A two wheel drive Common Rail 5.9 will if it's been taken care of. Example, my father's 06, which has a 35 gallon tank which I have driven from Austin, TX to Pueblo, CO on one tank with about an 1/8 of a tank to spare. The only thing it has that is different from the factory is LT285/70-17's instead of the OE LT275/65-17's which lowers engine speed by 150 rpm at 70 mph. LSD doesn't clog the cat like standard diesel does. The truck was bought new in September of 2006, LSD became standard in Texas in October 2006.

The LB7 was considered the most efficient of the 6.6's...from the factory. When you delete the emissions on an LBZ, you have an engine with better heads, injectors, tune, and a variable vane turbo. It also got a 6 speed allison where the LLY had a 5 speed, and the LB7 had a 4 speed. The 500 horse LBZ I speak of has a fully rebuilt Allison by Sun Coast with a lock up TC (which is who Dodge went to in order to get transmissions for the 2012 HO 6.7 which puts out 415 hp and 850 lb-ft).

I understand your reasoning about the larger engine part, but that really only holds true to American built engine. Take for instance the BMW M1. Has a 320 hp 3.0L flat 6, which you haven't seen here in the states in 50 years. M1 makes 37 mpg, which is better than most the 3.7 V6's running around (not just the Fords).