1st trip with our 2003 Knight with the Cummins 8.3 Great MPG

[JimC295]

I read somewhere that the 8.3 was much better on diesel than the 5.9 and seems like I remember 12-13 mpg. If I did not screw this up I got 13.4 with my toad in tow, WOW. I have a question though, is it normal for the tranny to not down shift with the accelerator floored? I changed the fluid and this was the 1st time I got it hot enough to run the diagnostics and turns out I was a couple of qts low. This is my 1st MH so not sure what normal is. Thanks in advance

[tmw188]

That mpg seems very high. 7.5-9+ is what I get.  I down shift manually when I need to. 

[Steve P]

6-7mpg for me @33,000 lbs towing 5,000 lbs

[JimC295]

Maybe I screwed it up. I've go  more legs on this trip so I'll keep checking it. I have not been down shifting but may start doing that. Just trying to understand what is normal. My main concern is on ramps and merging into traffic. I have not scaled it yet but GVWR is 27K and I towing a camry fairly light.

[tmw188]

Start your accelerating on the on ramp as soon as you can to get it going. I thought you were complaining about hills. 

[jacwjames]

I just did a 800 mile final run home with some of it in the E TN "large" hills!..   I look ahead and if possible I'll give it full throttle as I'm approaching a large hill.  If I time it right I gain enough momentum and can keep a pretty good speed up the long grades, most of the time doing better then most of the trucks.  If for some reason (traffic) I can't do that I'll be in the slow lane crawling up the grade. 

[JimC295]

Well, I guess my expectations were to high. I had a 2007 Ram with the Cummins 6.7 and on cruise it never dropped off cruise and it would fly down the on ramp if I floored it. I also had a tune in it so maybe I should think about that for this. I'm guessing I was pushing about 375hp and this one is rated at 300. But yall have given me some perspective.

[lake49068]

Very surprised at 10+ mpg!  If you're stopping your fuel fill when the pump turns off, you may not be adding the same amount as consumed.   My Neptune has a goofy fill neck and usually takes another 8-10 gallons after pump shutoff.  I use a flashlight and continue adding until it is visually up into the filler neck.  On our first long trip, actually ran out of fuel at the pump since I was mentally calculating published tank capacity x approximate mpg.  Gage was surprisingly accurate...as in E.  Was very lucky with location!

[jacwjames]

I just finished a ~4500 mile trip and according to my Silverleaf I got ~7 mpg, pulling a Jeep.  But a lot of the driving was in Co, Ut, AZ which can test your resolve at the fuel pumps.  The worse mileage got was battling winds going across KS, winds from the NW trying to push my rig off the road, it was stressful driving. 

My CC company got concerned when I filled 3 states in 2 days, sent me text and email alerts to check for fraud, but when your pumping $300 worth of fuel that should raise some flags.   NOPE that was all me.

[OhReally]

Make sure you haven't selected economy mode. That will make shifting sluggish.

 

[Steve P]

You may be able to change manually to a lower gear, but determine the most efficient RPM range for your engine and transmission.  In my case that is 1500-2000 rpm.  And if I press the pedal halfway, it may downshift one gear (5th to 4th, or 6th to 5th), that's all.  I just hit cruise to resume previous speed when I start down the on-ramp, and I'm usually doing 55ish when it's getting time to merge, and still increasing.  The truckers will move over if they can.   Both cars and truckers seem to slow down rather than crashing into a 55-60 foot long vehicle.  There is the occasional individual with the deluded certainty that they are indestructible and immortal.  Braking for them slightly keeps you clear of being the one to shatter their delusion, and screwing up your life.   Oh, be advised that mashing the pedal to the floor wastes fuel and gives the cylinder walls a bath, removing the oil that is needed for lubrication and therefore,  increasing friction and wear. 

[jacwjames]

2 minutes ago, Steve P said:

You may be able to change manually to a lower gear, but determine the most efficient RPM range for your engine and transmission.  In my case that is 1500-2000 rpm.  And if I press the pedal halfway, it may downshift one gear (5th to 4th, or 6th to 5th), that's all.  I just hit cruise to resume previous speed when I start down the on-ramp, and I'm usually doing 55ish when it's getting time to merge, and still increasing.  The truckers will move over if they can.   Both cars and truckers seem to slow down rather than crashing into a 55-60 foot long vehicle.  There is the occasional individual with the deluded certainty that they are indestructible and immortal.  Braking for them slightly keeps you clear of being the one to shatter their delusion, and screwing up your life.   Oh, be advised that mashing the pedal to the floor wastes fuel and gives the cylinder walls a bath, removing the oil that is needed for lubrication and therefore,  increasing friction and wear. 

Yesterday, between Nashville and Knoxville there are some pretty serious grades, I was following a truck and he was able to climb the grades pretty well.  There was a very very slow truck up ahead with flashers on and the truck I was following pulled out into the right lane to pass, I did the same thing.  All of a sudden a small car decided to make a 3rd lane and passed me on the left but there was a guard rail up ahead, I had to slam on my brakes to let him in, and as a "thank you" he flipped me a bird as he was stuck between me and the truck I was following.  What a jerk!!    I would have been ugly if I had not almost locked it up to let him in. 

 

 

[Steve P]

26 minutes ago, jacwjames said:

Yesterday, between Nashville and Knoxville there are some pretty serious grades, I was following a truck and he was able to climb the grades pretty well.  There was a very very slow truck up ahead with flashers on and the truck I was following pulled out into the right lane to pass, I did the same thing.  All of a sudden a small car decided to make a 3rd lane and passed me on the left but there was a guard rail up ahead, I had to slam on my brakes to let him in, and as a "thank you" he flipped me a bird as he was stuck between me and the truck I was following.  What a jerk!!    I would have been ugly if I had not almost locked it up to let him in. 

 

 

Sounds like one of those people who seriously believe everything bad that happens is the other person's fault. They can't seem to see the connection between reaping and sowing...  I just wave and smile big.  And pray he/she is not stupid enough to brake check me!  I no longer have my youthful reflexes!!

[jacwjames]

42 minutes ago, Steve P said:

Sounds like one of those people who seriously believe everything bad that happens is the other person's fault. They can't seem to see the connection between reaping and sowing...  I just wave and smile big.  And pray he/she is not stupid enough to brake check me!  I no longer have my youthful reflexes!!

Earlier in the day while merging onto I 30 it was heavy traffic but it was moving at a consistent pace.  All of a sudden the tractor trailer in front of me came to a screeching halt.  I locked up the brakes on my Windsor but with the rain not sure I was going to stop in time so I started to pull to the right side of the truck but there was a large SUV beside me doing the same as I was, they swerved to my passenger side.   Luckily no contact but it was iffy. 

I always try to leave room in front of me but everytime I get a good space there is usually a small car dart in between me and the vehicle I follow. 

But I know my brakes work really good. 

[JimC295]

10 hours ago, lake49068 said:

Very surprised at 10+ mpg!  If you're stopping your fuel fill when the pump turns off, you may not be adding the same amount as consumed.   My Neptune has a goofy fill neck and usually takes another 8-10 gallons after pump shutoff.  I use a flashlight and continue adding until it is visually up into the filler neck.  On our first long trip, actually ran out of fuel at the pump since I was mentally calculating published tank capacity x approximate mpg.  Gage was surprisingly accurate...as in E.  Was very lucky with location!

I ran mine over twice on my last 2 stops, truck pumps have a lot of volume. Flashlight is a good idea, thanks

[grizzly]

My 07 Sig with 600 HP turbo has averaged 6. mpg over 12000 miles pulling a 00 Toyota tundra and RV running at almost max weight for comparison

[dl_racing427]

Not to doubt you, but 12-13 MPG just seems unbelievable. 
Keep a running total over 10 or more tanks, and you may find it closer to 9 or 10.
I agree the 8.3 does quite well on fuel, but that's a lot more than anyone I've seen post here.

I tow closer to 9,000 # with my 36' Dynasty, and I'm usually in the 8-9MPG range.
If I ever drove it without the trailer, I suspect I could exceed 10, but not by much.

It's possible that your trip had an overall decrease in elevation, or a tailwind, which can both drastically affect mileage.
Another possibility is if your odometer is not accurate.
Some GPS devices can record cumulative mileage, and would be a good way to verify your odometers accuracy over a 1000 miles or so.

[JimC295]

8 hours ago, dl_racing427 said:

Not to doubt you, but 12-13 MPG just seems unbelievable. 
Keep a running total over 10 or more tanks, and you may find it closer to 9 or 10.
I agree the 8.3 does quite well on fuel, but that's a lot more than anyone I've seen post here.

I tow closer to 9,000 # with my 36' Dynasty, and I'm usually in the 8-9MPG range.
If I ever drove it without the trailer, I suspect I could exceed 10, but not by much.

It's possible that your trip had an overall decrease in elevation, or a tailwind, which can both drastically affect mileage.
Another possibility is if your odometer is not accurate.
Some GPS devices can record cumulative mileage, and would be a good way to verify your odometers accuracy over a 1000 miles or so.

David, I agree it seems high. I did have an elevation decrease. Where we live in N GA its about 1200 feet and I traveled to N FL. Im gonna track it the rest of the trip and  reevaluate.

[Ivylog]

Basing your MPG on one or two fill ups means little and 12+ isn’t going to happen as an average over 5000 miles. By leaning my rig after the nozzle shuts off I can add another 25 gallons making my mpg even worse. A 03 34’ has the advantage of weighing a lot less than most of us so my educated guess is your average will be 9-10 mpg at 62 mph. Report back in a couple of years.

Edited October 30, 2023 by Ivylog

[jacwjames]

When we first bought our rig I kept a log of fuel and expenses on a trip to AK.  +14K miles and averaged 8.3 mpg not pulling a toad.

There was a large variance in mpg from fill up to fill up. 

I don't really track mpg now other then monitoring my Silverleaf.

[Rikadoo]

Hello and good morning everyone, so last week i concluded my trip from Ca to Sc, what a great time. There were a few things i learned though, Not all truckers deserve the handle of “Knights of the road”, Nashville is NOT a sleepy quiet Country town, and fuel millage is all about 1 or 2 fill ups☹️

My trip from coast to coast was 5503 miles as per my GPS, which incudes my mistaken an lost event in St.Louis🤦‍♂️, like others before me i saw double didget mpg, then other times thinking as i was refueling it felt like i had just done this a few miles back. I had written down every fill up an recorded all my fill ups using my fuel mpg app. I primarily used Loves truck stops as my main source, with exception of Buckys for a fun stop with GREAT sandwhiches! 
All that said i learned alot about driving my 2003 HR Endeavor that has the Banks stinger kit, climbing hills i watched my EGT, climb to 1200 degrees and within seconds an no change to the throttle it would INSTANTLY drop to a hair over 1100degrees an stay there with no apparent loss of power. The pic shows a 3 month graph which i used cause to pick the one month would exclude too much info, my leave date was Sept 17th. Like was said earlier when filling the tank if i was or was not on a flat pad once the nozzel clicked off i would fether the nozzel an get another 8 to 10 gallons, also i used Diesel kleen exclusivly, not only for the mpg but it helps with reduced mirror shake when ideling, cold starts, AND improved exhaust smell. The entire fuel cost were just a few dollors over $3k, i was towing a dollie with a 1/2 ton pu, with a cruise setting of 65mph with exception of Ca which then was reduced to 59mph😜… Knock on wood the rig ran flawless an with exception of a certain amout of death defing drivers that thought there 💩 dont stink i got there an back with no major issues.

Oops meant to say Ca to Sc and back

[Rico K 2005 Knight]

On 10/27/2023 at 7:04 PM, JimC295 said:

I read somewhere that the 8.3 was much better on diesel than the 5.9 and seems like I remember 12-13 mpg. If I did not screw this up I got 13.4 with my toad in tow, WOW. I have a question though, is it normal for the tranny to not down shift with the accelerator floored? I changed the fluid and this was the 1st time I got it hot enough to run the diagnostics and turns out I was a couple of qts low. This is my 1st MH so not sure what normal is. Thanks in advance

I wish I could get that milage on my 2005 Knight. I'm getting 10 without towing and 8 when I am.

[tmw188]

It all depends on road conditions. Flat highway with very little if any hills, maybe no headwinds all makes a big difference, but the 13 with the towed seems really hard to achieve. 🤷

[JimC295]

I am headed home today, once I fill it up then I'll compute it again. So standby for an update.

[Rikadoo]

Mornin, so i been doing some thinking with what your saying… in that i often find myself going to Nevada to visit family or to take our can am out in the desert for a weekend of fun, and for the most part i top off each way before we leave one way or the other. The last trip there i figured when i was in Ca to save some $$ rather than pay the crazy amount for fuel that i could save some cash by doin the deed in Nv. I dont really pay attention to the mpg as to its all just part of the experiance, however the last visit to see family my nephew told me of the station he uses in Carson City, so i went there an filled up i was below 1/2. I kind of thought i was out of touch a little however as i was leaving the Carson valley it felt like the engine was running different, then over the sierras, same thing. When we got home i noticed i had used alot less fuel than my normal amount when i would return. Normally its somewhere between 1/4 to 1/2, this time it was like i only use 1/8. I shrugged it off thinking these fuel gauges can be “erratic” at times an this may be one of those times, so the next use was when i left for my SC trip, getting ready to leave it was in the same place so i did not top off leaving Ca. (The main reason was cost of fuel out here☹️) Once over the sierras i filled up in fernely nv as the gauge was still over 1/2 tank full??? I thought my gauge was having a real issue, cause now thats two crossings over the sierras an one of those ways im fully loaded an towing. It took only 49 gallons an after that fill up the sound an throttle responce went back to what i always remembered, then looking at the graph you can see the mpg did a steady climb untill i fueled in  fernley. So what ever that fuel was, i can say my rig not only performed better, but it responded to it even more. So all that said, i guess what i am saying is performance “can” be different than what we normally know based off of the quality of fuel, i know after writting that how of course it can be effected with gas engines, i just didnt think that it could be that much more for our DP’s. Well have a good Thursday✌️