F-550 Ford 6.4 Diesel

[john_bud]

SouthernX,

I have a 2008 F-550 with the 6.4L engine and 4.88 rear end. I only have 5,200 miles on the truck but have not had any issues to date. The truck averages between 7 and 8 mpg. Last week I pulled a 32' trailer (GVW was around 37,000#) for 250 miles on the highway. I checked my mileage when I got home and only got 6 mpg I went through both fuel tanks on the trip home.
Hope this helps.

Your experience is exactly in line with what others I've spoken to have gotten. They didn't have any issues with the truck between fuel stops, but make a LOT of fuel stops!

There is no comparison between a 250 and 550 for fuel economy - they just don't relate to each others. It's Apples to water melons.

 

[jcmseven]

john bud,

I fail to see why there should be such a huge difference in fuel economy, though. Diesels can pull additional weight fairly efficiently and although the mileage will drop assuredly, it should not drop by 5-6 mpg unless there were additional circumstances. The trucks share roughly the same frontal area and they are both bricks aerodynamically. The only other reason that I can think of would be the gearing, which is much more aggressive on the larger trucks, but would or should be moderated somewhat by the larger tires and wheels on the 550. I have never been able to fully figure out why the 6.4L is so thirsty. I know all the new diesels are thirsty and are struggling with emissions and maintaining power in the face of these changes, but I cannot understand why they do so poorly when one can get a big overroad diesel that does as well. My dad, when he ran a regional fuel distributorship, had several tankers that he used to haul fuel from the bulk plants to either large stations or his distributorship. As I recall they were/are Freightliners with Caterpillar 425 to 500 hp engines. They always pulled right at their 80,000 pound limit when loaded and got 6-7 mpg in hilly terrain. Why a 550 with the 6.4L cannot best that by several mpg's is a mystery to me, and I cannot see why it would be so much worse on fuel than my current pickup (I can understand worse, just not that much worse).

John M

 

[john_bud]

You that's actually a good question. I don't fully understand it either. The 550 is larger and taller than the 250, so that hurts. It's also heavier by 2-3000 pounds IIRC then add a 6-8000 pound tool box on the back. I thought the transmission had different gear ratios being lower in each range than the 250 too, but am not certain on that one. The difference with 3.73 and 4.88 is big. I would take a WAG that it puts the engine out of the economy sweet spot. I just know that the people with them are delighted when they hits double digits for mpgs, but that is about as often as a blue moon.

On the plus side, they have not had any major issues with the engine. Lots of power and pretty easy to start in the winter.

jb

ON edit, I think the extra weight of the bare truck + the tool box weight making the truck 8-10,000 pounds heavier than a F250 is 90% of the reason. (duh) An F550 "empty" weighs more than an F250 "full".

 

[pitt_md]

I only have 1500 miles on my 2008 F250 with the 6.4. I like the highway milage 19-20 mpg at 65mph, but do a little stop and go driving and your quickly in the 13-14 mpg range. Every time the boost meter goes past the halfway point (20lbs) the milage starts dropping like a rock.

 

[CampD]

I have an 08 F-250 supercab 4x4 with the 6.4L It now has over 20K on it and
average MPG's are 14-15 thats used solely for buisness and is run in the Mountians of W. Mass and Vermont.

Empty at a 55 mph it gets better then 17, sightly less at 65-70 which is were I usually drive at high speeds.

Towing various tractors mostly in the 10-12k range still averages 14
I frequently tow to Northern VT on the Highway (which is like a roller coaster ride) 200 mile trip and still average around 14 mpg

What 1 poster says about the boost is true, you peg the boost and the MPG's drop.

 

[Diamondpilot]

The tranny in a 250-550 is the same. Its like JB said, the weight is a killer. Also that 4.88 gear versus the 3.73 is a big difference. My F-350 with a 6L engine and 3.73 gears runs 78 mph at 1900 rpm, the sweet spot. Lets just say the 6.4L has the same sweet spot of 1900 rpm. With 4.88 gears it would only run 59 mph at that rpm. To go 78 mph he would have to run over 2400 rpm which is nearly 3/4 throttle which is a fuel drinking position on any truck or car by any manufacture. The good thing about the 4.88 gear is it will pull the world.

As for the big semi-trucks getting better mpg, they have 3 times as many gears to use. My buddy bought a 2007 Volvo pre DPF and gets 7-8mpg. His friend bought the same truck in a post DPF 2008 model and gets 5 mpg. Big deal when you are doing it for a living. What a F-350 dually and bigger really need is a high low rear end. This would give you the best of both worlds. Something like a 3.00 and a 4.88 or even lower in the 6.00 range would be awesome.

Chris

 

[Bird]

What a F-350 dually and bigger really need is a high low rear end. This would give you the best of both worlds.

All it takes is money. Of course it's been a long time ago, but I used to pull the fifth-wheel trailer we were living in with a 1989 Chev. one ton dually, extended cab, 454 cu. in. engine and 3-speed automatic with a 4.10 rear end. Adding the Gear Vendors Overdrive gave the same result as changing the rear end to a 3.20. It helped the gas mileage a great deal without the trailer. With the trailer, there wasn't as great a mileage increase, but was just a pleasure to drive.

 

[john_bud]

The tranny in a 250-550 is the same.

Chris

Really? Didn't know that. Is it the exact same with the same ratios in each gear too? I would have thought they may have gone to a deeper set of gears for the 2x weight.

Then again, I'm not making cars and trucks for a living...

jb

 

[GreenWannabe]

Really? Didn't know that. Is it the exact same with the same ratios in each gear too? I would have thought they may have gone to a deeper set of gears for the 2x weight.

Then again, I'm not making cars and trucks for a living...

jb

I think they achieve that by the rear end ratio - 3.73 for an F-250, 4.88 for an F-550 - and tire size. Plus the diesel is a lot stronger than just these trucks. International uses it in their DuraStar (4000) series mediums, actually derated from the Ford ratings.

 

[Compact1]

ON edit, I think the extra weight of the bare truck + the tool box weight making the truck 8-10,000 pounds heavier than a F250 is 90% of the reason. (duh) An F550 "empty" weighs more than an F250 "full".

Good point. I scaled my F-550 a couple of days ago and it weighed over 12,600 lbs Of course it has a custom bed, fuel tank, generator, air compressor, many tools, vice, etc. One of my trailers weighs 3,800 lbs. and the other weighs 8,000 lbs. It doesn't take much cargo to get into CDL range at those weights. My F-250 weighs 7,800 lbs...quite a difference!