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Jorg81 · 07-22-2018, **(Subject: Fuel Economy )**

I have a 2017 KW T680 with a Cummins CM 2350 475HP 3.36 rears 13 speed. I’ve always thought I should get better fuel mileage than I do. If I drive 55mph all the time, the best I average loaded is about 7mpg at best. Now I have a job that has required me to run much faster and obviously my mpg has gone way down, but even when driving slow, I have never thought my fuel economy was great. And this has been this way since it was new, so it’s not due to soot buildup. Am I just expecting better then I should be, or does my truck just suck for fuel economy the way it’s set up? I’ve seen a guy on YouTube with a W900 that gets way better than me and runs 70mph all the time. I thought my T680 would beat any long nose truck

Rounded_nut · 07-22-2018, **(Subject: Fuel Economy )**

What rpm, what type of trailer, what tires, etc etc.

I pull a cattle pot, even going slow best I can hope for is 5.8 in a Pete 389.

Jorg81 · 07-22-2018, **(Subject: Fuel Economy )**

(07-22-2018 )Rounded_nut Wrote: What rpm, what type of trailer, what tires, etc etc.

I pull a cattle pot, even going slow best I can hope for is 5.8 in a Pete 389.

Well if I go 55mph, that’s around 1200 rpm on a flat surface. Tires are 22.5 Micheline X line energy on steers and drives. Dry van trailer with Bridgestone 22.5. Your 389 Pete is not known for good fuel economy but a T680 usually is

Rawze · 07-22-2018, **(Subject: Fuel Economy )**

One problem you have is those 3.36 rears. They absolutely suck the life out of your truck and its fuel economy as soon as you put a load on the trailer. they also shorten engine life. I would like to smack the pencil-pushing complete idiot who came up with such a horrible idea in a big truck up side the head with a hammer.

Jorg81 · 07-22-2018, **(Subject: Fuel Economy )**

(07-22-2018 )Rawze Wrote: One problem you have is those 3.36 rears. They absolutely suck the life out of your truck and its fuel economy as soon as you put a load on the trailer. they also shorten engine life. I would like to smack the pencil-pushing complete idiot who came up with such a horrible idea in a big truck up side the head with a hammer.

I don’t know enough yet to understand what the best rear end ratios are or which ones are bad. That sucks mine are bad. Guess I can’t change that though without spending a fortune.

hhow55 · 07-22-2018, **(Subject: Fuel Economy )**

(07-22-2018 )Jorg81 Wrote:
(07-22-2018 )Rawze Wrote: One problem you have is those 3.36 rears. They absolutely suck the life out of your truck and its fuel economy as soon as you put a load on the trailer. they also shorten engine life. I would like to smack the pencil-pushing complete idiot who came up with such a horrible idea in a big truck up side the head with a hammer.

I don’t know enough yet to understand what the best rear end ratios are or which ones are bad. That sucks mine are bad. Guess I can’t change that though without spending a fortune.

Since you have a 13 tranny, my choice would be 3.70

Rawze · 07-22-2018, **(Subject: Fuel Economy )**

(07-22-2018 )Jorg81 Wrote: ...
Guess I can’t change that though without spending a fortune.

usually costs about $3k or so to change them out with remans.

optimize what you got first, drive by your boost and pyro gauges and gear down early when you need any kind of torque. Go through your enfgine and make sure it is running its best, pressurize whole engine and look for intake and exhaust leaks,.. etc. etc. etc. - Possibly custom tuning for better fuel mileage instead of more power while your at it.

Jorg81 · 07-22-2018, **(Subject: Fuel Economy )**

(07-22-2018 )Rawze Wrote:
(07-22-2018 )Jorg81 Wrote: ...
Guess I can’t change that though without spending a fortune.

usually costs about $3k or so to change them out with remans.

optimize what you got first, drive by your boost and pyro gauges and gear down early when you need any kind of torque. Go through your enfgine and make sure it is running its best, pressurize whole engine and look for intake and exhaust leaks,.. etc. etc. etc. - Possibly custom tuning for better fuel mileage instead of more power while your at it.

I do want to learn how to do all these pressure tests. I have yet to learn how to do them. I’ve got pretty much the same kind of fuel mileage since brand new though. I need to add the gages as well. I also have a job that pretty much requires me to run fast right now, but it also pays off big to do it, but I had a dedicated route before and ran 55 all the time and still struggled to get 7mpg at the very high end. I did start dropping gears like you said and using my horsepower rather than torque to pull hills. I have a ton to learn. I’m still about as green as you can get when it comes to knowing about trucks and working on them. But I’m determined to keep learning even if it takes me forever. I’m definitely not a natural mechanic

Jorg81 · 07-22-2018, **(Subject: Fuel Economy )**

I did pull my IMAP sensor today though and cleaned it, and researched in quickserve all day and learned a lot and now understand where more things are at and how they are routed. I think I can handle doing most of the EGR tuneup now except it looks like my intake manifold may be hard to get off. Looks harder on my 2350 than the 871 I saw you do Rawze. I seem to have a lot of bundles of wires zip tied in the way. I’m afraid to mess up anything. But I think I can handle pulling the EGR valve, and Doser, and probably the EGR tube, Ect....