CM871 fuel mileage

[superbudy208]

So like I said the fuel mileage get worse i suspect because it lugs the motor down around 1250 to 1300 rpms, so sounds like gears are needed, the truck does like to run 70 to 72 mph and the engine runs around 1400 to 1500 rpms and seems happy, today driving the truck i can not get the engine to rev past 1700 in 8th or 9th gear and will slow down from 1700 rpms down to 1500 before it goes again kinda strange!

So the original data plate is missing because it appears the valve cover has been changed, I still need to get the paper work and read over every line by line! ESN for the truck is 79281998, I'm not sure how to post a pic in here yet this is the first forum I've been on. When i tried talking to the dealer they made it seem like it was normal but, as I've been driving and fixing things on the truck I can also tell the fixed the problem but not the issue that caused the problem, like the truck got 2 transmission's one from pete and one from kenworth, but they did not replace the shifter and found it was not shifting out of reverse all the way and that was a bad trip at 3 mpg's

Also don't have insite yet but the adapter is in the mail and should be here by Friday

So I do know it had new Cummins cylinder head installed, but not sure on the numbers but I will get them in the next tomorrow, just got home and the wife has surgery and will be down for a few days.

No I don't think another over head was done at 50k when I talked to the owner about it he said it don't need one till 500k but the weather was horrible so had the dealer do it, but no difference was felt.

No I have not pressure tested the system but I can do that, and there's no fuel leaks it did have fuel line's that were coming apart, and all the fuel lines have been replaced, from front to rear going both directions with all new fittings and I better get some wedges to check the timing.

Also suspect maybe a chassis problem of the rear axles there are several shims on one side and I do know the front shackles need to be replaced and has a slight clunk at times ,and the right front axle inner tire has a funny wear pattern in it.

[Rawze]

That thing sounds like it has been a severely neglected truck most of its life.

[superbudy208]

Yeah the owner made it seem like it was taking care of had lots of paper work always kept up on oil changes, and said the truck always got 5.5 mpg's when I bought it, but i did not do my own research on fuel mileage on trucks and the guys I've talked to said that was good but also there all local guys, I know I didn't purchase the best truck but for the price with all the paper work, it seemed like I got a good deal. but now I'm not so sure. but im committed now,so it is what it is.

[SquareOne]

I just got into this industry myself..only right over 2yrs ago, and I found that plenty of 'old school' truckers who have been lifers seem to say the same things about fuel mpg in general.

In fact, the guy who often runs with me has been trucking for the better part of 5 decades, yet rather than read the writing on the wall (i.e. slowing down will net better mpg), he continues to tell me (the newbie) that these trucks will get 4-5mpg regardless just cause 'thats what they get and will always get.'

Oddly enough, whenever we pull up to the pump, his bill is nearly double mine for the same miles traveled....yet he still believes in his old school ways. Maybe this why he no longer owns any trucks <------claims there just isn't much money in it anymore..hmmmm?

Moral of the story being, def do your research and take no one's word for anything without some concrete data. Everyone has an opinion, but many are 'fact-less' based. Just because they failed for whatever reason, they like to point out all the excuses for it rather than address the real issue....usually the person in the mirror. You're in the right place to learn more than you may be willing to absorb.

[Lead_sled]

My fuel mileage sucks, but for other reasons. I drive 40-60 mile routes with slowing down and speeding up in small towns. Also, red lights and rolling hills. The truck also idles when waiting to be loaded and unloaded. On top of that, truck idles for my 8 hr resets. The trailer I pull is just a chassis, but the box that goes on it is like a wind sail. It sits about 15-20’ behind the cab. I still manage to get an average of 4.5 mpg.

[Rawze]

(05-13-2021 )Lead_sled Wrote:  My fuel mileage sucks, but for other reasons. I drive 40-60 mile routes with slowing down and speeding up in small towns. Also, red lights and rolling hills. The truck also idles when waiting to be loaded and unloaded. On top of that, truck idles for my 8 hr resets. The trailer I pull is just a chassis, but the box that goes on it is like a wind sail. It sits about 15-20’ behind the cab. I still manage to get an average of 4.5 mpg.

if your a lot of stop and go... city and local .. then a set of 4.36's do wonders for that.

[gearratio]

(05-10-2021 )Waterloo Wrote:  I'm one of those past luggers, I had to relearn how to drive too... Now in the high 6's with a mid roof pulling a van. If I had a flatbed, I could do 8+ all day long.

you're one i'm watching and learning from,we just rebuilt my 871 535hp to the rear wheels 1850 ft lbs gearratio is 3.90 this should be a nice combination up to 65mph

[Waterloo]

(05-14-2021 )gearratio Wrote:  

(05-10-2021 )Waterloo Wrote:  I'm one of those past luggers, I had to relearn how to drive too... Now in the high 6's with a mid roof pulling a van. If I had a flatbed, I could do 8+ all day long.

you're one i'm watching and learning from,we just rebuilt my 871 535hp to the rear wheels 1850 ft lbs gearratio is 3.90 this should be a nice combination up to 65mph

I had 3:90's on an old Volvo/White unit, 8 mpg all day long at 65mph... I miss that truck.

[superbudy208]

Going to get the EGR tune up done this weekend and install the boost gauge, and the pyro gauge, so I see RAWZE clamps it to the manifold what temps should I be looking for with it like that?