MPG frustration

[bread519]

So from what I've gathered online, it seems like most DT466 users are getting roughly 9-12 mpg. Mine is still only getting 7.5-8, doesn't seem like the foot or towing the toad is making a difference at all.

My trip this past weekend was 600 miles, just myself and 3 guys. Not a ton of gear at all. I kept it at 60 the way there (2350 rpm), and noticed that I was getting pretty poor mileage. So on the way home decided to slow down to 55 (2200 rpm), and still only got 7.75 mpg.

A few things I haven't checked, tire pressure and fuel filter. But could either of these things really be hurting me this much?

The drive had hills, some of which required the pedal to the metal, but not too many more hills than I would expect a normal trip would have. Idk. What do you guys think

 

[BurlKing]

depends on quite a bit. the gear you are in, the rpms you're going, tire pressure and wear on the tire, quality of fuel and oil as well as both of those filters.

 

[milkmania]

depends on quite a bit. the gear you are in, the rpms you're going, tire pressure and wear on the tire, quality of fuel and oil as well as both of those filters.

And air cleaner restriction... My gauge shows 2% resistance at this time.

 

[aaronsb]

Worn injector nozzles can really cause the fuel to get consumes too. If the injectors don't atomize, it takes way more fuel to make the power.

What's your exhaust look like when climbing a grade? What's EGT look like?

So from what I've gathered online, it seems like most DT466 users are getting roughly 9-12 mpg. Mine is still only getting 7.5-8, doesn't seem like the foot or towing the toad is making a difference at all.

My trip this past weekend was 600 miles, just myself and 3 guys. Not a ton of gear at all. I kept it at 60 the way there (2350 rpm), and noticed that I was getting pretty poor mileage. So on the way home decided to slow down to 55 (2200 rpm), and still only got 7.75 mpg.

A few things I haven't checked, tire pressure and fuel filter. But could either of these things really be hurting me this much?

The drive had hills, some of which required the pedal to the metal, but not too many more hills than I would expect a normal trip would have. Idk. What do you guys think

 

[Crazy]

Your post doesn't tell anyone anything about your bus. We know what engine. What about the transmission, tire size, rearend gear ratio, miles on the bus. How about helping us help you.

 

[bread519]

Transmission is MT643

Rear end is 4.78 (I listed the RPM so that should be sufficient anyways)

Mileage is 115k


I'm not seeing any smoke at all really ever. Except for when I first start the bus. The air filter gauge says I have plenty of life left, but idk how accurate that is

I do have a pyrometer, but it's not working

 

[Crazy]

Still didn't put all the info but I'll take a stab at it. The 4.78 is the same as one of my buses. For me, that is more of a ratio for an around town bus than a freeway bus. I drove back from Texas at speeds between 45 and 50 mph. I am comfortable having the engine at 2000 rpm. I think that is the sweet spot. This is not the same as a VW 1.9 TDI. I know they make a 4.44 and a 4.10 rearend. I am posting a link for you to check the rpm for different factor. You could also go up in tire size.

Engine RPM Calculator

 

[bread519]

Still didn't put all the info but I'll take a stab at it. The 4.78 is the same as one of my buses. For me, that is more of a ratio for an around town bus than a freeway bus. I drove back from Texas at speeds between 45 and 50 mph. I am comfortable having the engine at 2000 rpm. I think that is the sweet spot. This is not the same as a VW 1.9 TDI. I know they make a 4.44 and a 4.10 rearend. I am posting a link for you to check the rpm for different factor. You could also go up in tire size.

Engine RPM Calculator

Yea that seems to be the sweet spot for me as well. I'll grab my tire size tomorrow I haven't been out by the bus today. I really want to change the rear end size I think. does anyone know where to start on finding the part #s I need? I will get the model # of the rear end tomorrow. I know it's spicer

 

[cadillackid]

the slower you go the less wind resistance which is huge for most of our busses that have nearly 90 degree front ends.. ive done well running mine at 60.. but this next trip I may try 55 just to see if theres a difference.. since I have a 545 trans my RPMS tend to run up a bit anyway just due to the stall speed on the torque converter being at the max power-band of the DT-360

of course re-gearing to say 4.44 can help your top speed however it gives you less leverage against the road so you may run out of engine much easier on hills than you did previously... downshifting to 3 helps in that situation and ofcourse your top speed in 3 is higher wit ha different gear.. but in a bus im thinking you wouldnt go any taller than a 4.44? maybe im wrong about that... a 4.11 would definitely bring your RPMs down...

depending on availability of parts and cost to regear, aother option is a tranny swap to an over-drive unit.. a 1000 or 2000 series.. not cheap.. but i also know re-gears arent cheap depending on the rear you have also...

-Christopher

 

[bread519]

I'll just sell it and get a different bus if I can't get 9-10 mpg at that point

I have 11 r 22.5 tires so with 4.10 gears I would have 2011 RPM at 60 mph which would be perfect I think. I don't mind slowing down for hills if I can go faster on the interstate which is the majority of my mileage in the midwest

 

[bread519]

All I know is I've read that numerous semis have this engine and get 10-12 mpg at 2200-2600 rpm according to some other diesel forums. Are busses that much different than a loaded semi? I've read plenty of people getting 10 mpg with a DT466 at AT545 so I thought I'd get as good or maybe even better with my lockup trans idk

 

[cadillackid]

even the appalachains , poconos, and smokies arent bad.. i just have a DT-360 with AT545 and 4.78 gears.. theres only 1 or 2 hills that I have slowed below 55 on.. and I figure ive got a lot less power at my wheels than you do having a 466 and an MT643..

ive got 11R22.5 tires now.. whats wierd is im getting that 9-11 MPG range running at 60 on the highway.. I dropped sigificantly when I ran my bus at its top speed of 65-68.. like in that 6-8 category...


-Christopher

 

[Carytowncat]

I will just set this here...

 

[bread519]

even the appalachains , poconos, and smokies arent bad.. i just have a DT-360 with AT545 and 4.78 gears.. theres only 1 or 2 hills that I have slowed below 55 on.. and I figure ive got a lot less power at my wheels than you do having a 466 and an MT643..

ive got 11R22.5 tires now.. whats wierd is im getting that 9-11 MPG range running at 60 on the highway.. I dropped sigificantly when I ran my bus at its top speed of 65-68.. like in that 6-8 category...


-Christopher

That's the range I am expecting with mine. I don't think it's out of range at all. Something has to be wrong

 

[bread519]

I will just set this here...

I've actually seen this thing before haha

 

[Brad_SwiftFur]

Are you sure your speedometer/odometer are correct? Changing tire sizes can throw it off. How are you calculating the miles driven?

Aaron mentioned injectors ... old/worn/bad injectors can hurt fuel mileage, so you might want to check into that, if you haven't already. Mechanical injector pumps can as well. One old farmer I worked for had a couple F-350 trucks with 7.3 engines and one of them would consume ~40 gallons of fuel on a 200 mile trip. The other did somewhat better, averaging ~25 gallons on the same 200 mile trip. These were typical 16 foot box trucks, which should have been able to manage better than 10 MPG with these engines ... the fuel systems had a lot of miles and presumably never replaced, AFAIK.

 

[cadillackid]

omne thing I hadnt thought of is injector timing is Crucial to MPG's.. I dont know how the 'E' variants of the engines handle it.. i know on the mechanical pumps it is easy to remove the inspection cover and check what the injector timing is set at...

imjector timing on a diesel is effective to the spark timing on a gasoline engine.. and greatly affects power output and burn quality in the cylinders..

-Christopher

 

[bread519]

omne thing I hadnt thought of is injector timing is Crucial to MPG's.. I dont know how the 'E' variants of the engines handle it.. i know on the mechanical pumps it is easy to remove the inspection cover and check what the injector timing is set at...

imjector timing on a diesel is effective to the spark timing on a gasoline engine.. and greatly affects power output and burn quality in the cylinders..

-Christopher

If the timing was incorrect would I have any side affects? The rig seems to have power to spare but I've also never driven any other buses

 

[International]

So from what I've gathered online, it seems like most DT466 users are getting roughly 9-12 mpg. Mine is still only getting 7.5-8, doesn't seem like the foot or towing the toad is making a difference at all.

My trip this past weekend was 600 miles, just myself and 3 guys. Not a ton of gear at all. I kept it at 60 the way there (2350 rpm), and noticed that I was getting pretty poor mileage. So on the way home decided to slow down to 55 (2200 rpm), and still only got 7.75 mpg.

A few things I haven't checked, tire pressure and fuel filter. But could either of these things really be hurting me this much?

The drive had hills, some of which required the pedal to the metal, but not too many more hills than I would expect a normal trip would have. Idk. What do you guys think

We have a 7.3 deisel and was having bad gas milage. A trucker at a truck stop told us to put some Lucas Deisel Treament in it to clean injectors,etc..
It not only had better milage but also ran better.

Far as hills go our Shorty really hates hills, it slows down on the long high ones to 35mph, which is bad and maybe against the law? .

Wife of International

 

[turf]

my bus has always been a 7-9mpg bus. i drive with the foot to the floor all the time. that gets 60-67mph.

on my first trip this summer, i caravan-ed with another skoolie, at about 5mph slower than foot to the floor. 55-60

i didnt get to check my fuel mileage, but the needle never moved off of full for the 2 hours or so that we drove together. after they turned off, i sped up and the gauge started moving like usual.