[JetMechPilot]

I know I know, another mileage thread.

2006 5.9 Megacab
4x4
Auto
Level kit
285/75R17
3.73 gears
131,000 miles
4" exhaust with muffler behind the cab

I am not going to whine about poor mileage so much, but I am curious your thoughts. I consistently get about 15.2-15.6 mpg, hand calculated. GPS mileage (not odometer mileage) divided by gallons in the tank. I drive 80 highway miles a day to work and back, and rarely on weekends. Typically getting about 460 miles a tank. I drive very conservatively, and the only time I get on the gas to amount to anything is getting on the interstate which is still slow to be honest.

What I am curious about is that I have made a LOT of changes to the truck in pursuit of better mileage, and NOTHING seems to change the mileage at all. Below is a list of the way things have gone since I got the truck and started really tracking it:
- S&B intake without the block off plate installed, then with the block off plate, Smarty JR latest software
-- In this configuration, I tried tons of combinations of tunes from the SJR. Let them each go through 2-3 tanks of diesel, no change. SW1, 2, and 3, with all different combos of timing and torque, even "stock" under each SW#.
- Removed S&B, installed stock intake, ran through a lot of SJR tunes. No change.
- Stock intake, change from ~74 mph (1900 rpm) on highway to ~70 mph (1800 rpm), no change in mileage.
- Stock intake, removed SJR altogether. No change.

All the changes I have made, I let them run for a few tanks and see what happens, but no matter what, the mileage stays consistent. Which really baffles me as the tunes I know are doing different things with the engine because I can hear it and feel it. But mileage just stays the same.

My next step is to check the valve lash, as it *sounds* a bit noisy, but in all honesty, I don't know enough about the Cummins to say one way or the other.

Any thoughts? Any questions about my setup that you might need to know? I have a hard time believing people are getting 20+ mpg with 35s when I drive like a grandma on 33s in a mostly stock truck and can't break 16 mpg no matter what I do.

 

[the man in black]

What people claim and what they get are 2 completely different things. 20+ on 35s is difficult to believe.
If you want to see an improvement look up steve05ram or something. He has tons of data on mileage.
8d say you need to loose the level and slow down if you want to see a quick improvement. Going over 70 creates a lot of drag which may be why you didn't see an improvement going from 74 to 70. Same goes for the tires. What type of tread are they? Heavy at or mt will suck more fuel than a lighter weight tire.

 

[Gildo]

Your miles per gallons is dead on where mine is, and where mine has always been. Of course the previous owner of my 07' claimed 23mpg, the day I bought it, 15mpg, go figure. My last F350 7.3L got the same mileage and a good friend has had three Dodge 5.9L diesels and one Ford 7.3L diesel and they all got around 15mpg, and none would get 16mpg. I suggest that you would be better off if you don't believe all the hype on these forums about 20+mpg. One guy on this forum claimed 28mpg. Mine won't get 20mpg driving downhill all the time. These are 7,500lbs trucks, some weigh more and they have the aerodynamic characteristics of a brick.

Lots of people have offered to prove me wrong. I'm still waiting. I'd love to see it.

Yours is exactly where it is supposed to be.

Gil

 

[JetMechPilot]

Thanks guys. I’m running BFG ATs. Like I said I’m not complaining. This has been one of my favorite vehicles I’ve ever had and I have no plans for getting rid of it. I have afforded the fuel with no issues. Mostly just curious why all these changes have resulted in 0 change in MPGs. But I guess I’ll just move on.

 

[GRUNT 11B]

Checkout some of Steve's threads.

https://www.cumminsforum.com/forum/3rd-gen-powertrain/2014730-mpg-threads.html#post23312562

I know you said you drive conservatively, but I've found that my acceleration has a lot to do with fuel mileage. If stop and go with the flow of traffic, or slightly slower, I'll get around 16-17 MPG. If accelerate super slow to where people go around and pass me, engine load doesn't see 20%+, i shift from 1500-1800 and go the speed limit or like 5-10 under on highways and freeways i can hit 20 MPG.

 

[dshupe24]

This may or may not be helpful, but when I had my second gen It would consistently get 14-16 mpg when I first got it, It had a level kit and 35s. I swapped to 33s and picked up 1 mpg on average a few months later I returned it to stock height and went down to 31s, after that i consistently got 16-18 mpg. That was with virtually no freeway driving. Hope this helps!

 

[twildman]

There is a lot to take into consideration first. Where are you located, altitude or sea level. How much stop and go on the way to work do you deal with? How much idle time does the truck get? Do you use any additives in your fuel? What oil do you use?

Free spinning hubs will make a difference, lowering the truck will help, smaller tires and lighter wheels will help as well. One piece aluminum driveshaft will add a little.

 

[verdesardog]

Free spin hubs will make negligible difference in fuel milage! My 06 gets 14-16 around town or off road. 18-19 on a good interstate.
Leveled, free spin hubs with 315-70-17 tires. Completly stock engine/drive train auto trans, no programmer.

 

[steve05ram360]

Free spin hubs will make negligible difference in fuel milage! My 06 gets 14-16 around town or off road. 18-19 on a good interstate.
Leveled, free spin hubs with 315-70-17 tires. Completly stock engine/drive train auto trans, no programmer.

Maybe its time to do an A-B-A test with mine on the commute to work... just need the weather to be roughly the same for each test. My truck mpg is pretty repeatable if I am able to keep my foot out of it. Back in MN I measured ~0.8 mpg on back to back test runs in freezing weather... that was the 120~125 mi hiway run out & back (~60 ea way) using CC set @ 64.

Having dropped the 13# off the rear driveshaft and then the 36# off the wheels, I cant see how it does not improve mpg since unlocked your no longer driving the axles and front driveshaft.

Edit: nice truck btw...

 

[steve05ram360]

Your miles per gallons is dead on where mine is, and where mine has always been. Of course the previous owner of my 07' claimed 23mpg, the day I bought it, 15mpg, go figure. My last F350 7.3L got the same mileage and a good friend has had three Dodge 5.9L diesels and one Ford 7.3L diesel and they all got around 15mpg, and none would get 16mpg. I suggest that you would be better off if you don't believe all the hype on these forums about 20+mpg. One guy on this forum claimed 28mpg. Mine won't get 20mpg driving downhill all the time. These are 7,500lbs trucks, some weigh more and they have the aerodynamic characteristics of a brick.

Lots of people have offered to prove me wrong. I'm still waiting. I'd love to see it.

Yours is exactly where it is supposed to be.

Gil

Flashback for a semi-quick story... when I did my tranny swap a CF member pinged me on my trans & converter. He wanted to swap his out since they were OEM & mine was built mildly, TC was a nothing special HD unit with 160k miles on it. Him being from the Fresno area & me up in Sacramento, met him half way for him to test drive it. All was good and we set up a swap date @ the trans shop that had rebuilt that trans 2x. (First failure was an oem part that failed from the facotry, 2nd failure was the heat exchanger that failed & took out the trans).

Met the guy @ the trans shop & started yapping it up. Come to find out he had always measured his mpg since he bought the truck new. 2006 MC 4x4 with 4" lift (iirc) on 20" chrome wheels. Me mentioned he got ~12.5 mpg (dont recall the exact number but it was in the 12's) on way up. First question from me was "Hand calculated?"... yup, always. Swap goes off without issues and he is on his way the next day. That evening I get a call from him... my first thought, "awe crap something broke...". Phone answered and the guy was so happy... hand calculated ~18.0 mpg on the way home. Chatting it up for a bit he mentioned he never saw anything greater than 14's since he owned it. I asked him to stay in touch for a few tanks and let me know how it does with normal usage after he gets back to his normal routines. Few weeks later I get a text say his mpg stayed in the 17's for every tank, (mostly hiway I'd assume). I believe there was that there was some issue with his OEM setup.

All this is mentioned in a thread on here in the April-May 2015 time frame if anyone wanted to search for it.

FWIW, back then 17~18 mpg was the norm with the AT and my 3" leveled truck. 20 mpg was extremely rare.

 

[steve05ram360]

I know I know, another mileage thread.

2006 5.9 Megacab
4x4
Auto
Level kit
285/75R17
3.73 gears
131,000 miles
4" exhaust with muffler behind the cab

I am not going to whine about poor mileage so much, but I am curious your thoughts. I consistently get about 15.2-15.6 mpg, hand calculated. GPS mileage (not odometer mileage) divided by gallons in the tank. I drive 80 highway miles a day to work and back, and rarely on weekends. Typically getting about 460 miles a tank. I drive very conservatively, and the only time I get on the gas to amount to anything is getting on the interstate which is still slow to be honest.

What I am curious about is that I have made a LOT of changes to the truck in pursuit of better mileage, and NOTHING seems to change the mileage at all. Below is a list of the way things have gone since I got the truck and started really tracking it:
- S&B intake without the block off plate installed, then with the block off plate, Smarty JR latest software
-- In this configuration, I tried tons of combinations of tunes from the SJR. Let them each go through 2-3 tanks of diesel, no change. SW1, 2, and 3, with all different combos of timing and torque, even "stock" under each SW#.
- Removed S&B, installed stock intake, ran through a lot of SJR tunes. No change.
- Stock intake, change from ~74 mph (1900 rpm) on highway to ~70 mph (1800 rpm), no change in mileage.
- Stock intake, removed SJR altogether. No change.

All the changes I have made, I let them run for a few tanks and see what happens, but no matter what, the mileage stays consistent. Which really baffles me as the tunes I know are doing different things with the engine because I can hear it and feel it. But mileage just stays the same.

My next step is to check the valve lash, as it *sounds* a bit noisy, but in all honesty, I don't know enough about the Cummins to say one way or the other.

Any thoughts? Any questions about my setup that you might need to know? I have a hard time believing people are getting 20+ mpg with 35s when I drive like a grandma on 33s in a mostly stock truck and can't break 16 mpg no matter what I do.

Sounds to me like your determined to make it better... I'd suggest taking it a step back, go back to stock programming and S&B intake with the bottom closed (better than the oem airbox with the oem hose to the turbo IMO, best is the stock airbox & AFE torque tube or Cool Hose). Once your there, establish a baseline for where your at with mpg. Consistent driving is key, CC helps with that if your on the flats. Any hills you encounter take CC off and hold throttle steady before the base of the hill & on the grade allow speed to drop a tad bit (5 mph max is what I do) and resist rolling onto the throttle. Leverage gravity on the back side as much as possible.

ONce your consistent with that, swap in a 200*f t-stat, good for approx 0.8 mpg on stock programming. If your not towing and dont have steep grades to climb, unplug the fan clutch. If you dont already have a way of monitoring the obd port, fix that next. You want to see what IATs & CTs are doing and make sure the CTs are OK. Once your there, get a front cover to go over the cooling stack (Genos sells one, or make one for under $25 bux) and cover it up. Make sure you monitor trans temps... You'll want to drive intake temps up into the 80's or greater if possible.

Once all that is done, I would not be surprised to see a ~1.5 mpg bump from baseline mpgs. After that, then add back in any programming and see how it performs.

If you have your silencer ring removed, put it back in. Its one of those things that you wont be able to tell one way or the other as to what its doing but it is one that will add up with other smaller mpg improvers. When I went to my current HTT HE351 stage 2.5 turbo, the ring was out. Installed it at one point and saw intake temps rise slightly and noticed a decent bump in low/mid power. Asked a turbo shop guy who was on here about it via PM and he mentioned the ring was removing turbulence that exists in front of the compressor wheel and was compressing more air. With the modded turbo it was more obvious as to its effects.

For reference... my truck...


Before:

2" leveling springs, H2 wheels (30# ea) ~5/8" rear block from the oem setup with full leaf pack conversion. 19-20 mpg all day long in the summer months, 21 if I really REALLY tried.

After:

Makeover done in 2018, 2010-2012 OEM alloys (dropped 36# of rotational mass), stock height, added rear block removed, aluminum driveshaft (dropped 13# of rotational mass). Best tanks were in the 23's in the summer months. Now in cooler weather and winterized D2 I struggle to get into the 20's. Best recent tank under ideal conditions was a 21.6 mpg, (no rains or winds and a short mileage filled tank)

Get warmer air mods:
front grille block, does two things, 1st directs some of the air over the hood vs into the engine compartment, 2nd, allows engine compartment air to warm up more in cold weather.

My e-fan setup (volvo fans)

CAC blanket... this is between the radiator and the CAC. The metal strap is there to prevent the blanket from being pulled away from the CAC when the e-fans are on.

CAC blanket from the top. Marine grade vinyl, $12 for a 54"x24" piece.

Original front cover I made back in MN. Blocks airflow on the sides to force air to be drawn in from the engine compartment. Note that the air deflector next to the radiator is removed (cannot be seen).

My truck is an exception on the mpg front... a lot of other mods that all add up, minor aero mods, custom tuning plus I have a late G56 trans with taller gearing (2000 rpms =~70 mph)

 

[steve05ram360]

Oh yeah, your tires... 285-70-17's would be better in hilly conditions & in the city, less rotating mass to get going and keep going up grades. The taller tire is better (I think) on the flats & for hiway use.

I tried a set of 285-75s recently and mpg was down even farther, 19's were a good tank. Ran that tire for approx 2000 miles on a "Buy & try" thing the tire shop had and hated every minute of it. Went back to the 70's and ~1 mpg came back that day. (I'm in the Seattle area, nothing is flat here)

 

[JetMechPilot]

Thanks for the fast responses!

My 80 mile commute is probably 85-90% highway with cruise control on. But it is a bit hilly. I'm south of Nashville TN. Little idle time. Stock Laramie wheels. No fuel additives. I use Baldwin fuel filters every 5k miles. Rosella T5 15W40. Silencer ring is in.

And I have definitely read Steves threads. I have one saved as a favorite on my phone haha. I was mostly curious how all these changes wouldn't indicate any MPG change. Regardless of how good or bad it may be, I just can't believe it hasn't been ANY change. The only change I ever saw was going from stock size tires to the 285/75s. I lost ~1.2 mpg. That doesn't ruin my life or anything but at least I saw a change. I figured with a regularly repeatable drive (good testing scenario) that changing certain things would yield some sort of result. That's all.

That said, I will definitely attempt a few of the things you guys have laid out and see what happens. I have nothing but time so it will be slow going. But I'll do it. I'm keeping the tires. But I'll try the SB intake first. I'm already on the stock reflash.

What does unplugging the fan clutch do? Will I permanently lose the fan if I do that?

My next steps then will be SB intake and valve clearance checks. I had also pondered about the transmission being a reason but is there anything I can do with mine to check it? Tighten the bands? Drain and refill? It's completely stock. What made me think about it being a culprit is the lack of change with my tunes and mods, as if no matter what I did, something else was making the truck work harder than it has too like a drag on the system. I guess I should make sure my brakes are free too.

Regardless. It is an awesome truck and I'm proud to own and drive it. Thanks fellas.

 

[GRUNT 11B]

If you mostly drive highways, just try driving like 5 MPH slower to and from your destination. You might only have to leave 10 minutes earlier. Try that for a tank or 2 and see what happens. What is the speed limit and how fast are you driving?

Sent from my SM-G930V using Tapatalk

 

[steve05ram360]

There is a 25* limit between the airbox temp and IATs, once your passing that temp, the fan clutch will engage and mpg suffers. You can eliminate it in custom tuning.

What muffler is where the cat was?

Since your in rolling hills take that up hill suggestion i had and also drop speed to 65 as grunt suggested. Your losing mpg on the uphill sides as would be expected, holding throttle works better going uphill.

 

[JetMechPilot]

If you mostly drive highways, just try driving like 5 MPH slower to and from your destination. You might only have to leave 10 minutes earlier. Try that for a tank or 2 and see what happens. What is the speed limit and how fast are you driving?

Sent from my SM-G930V using Tapatalk

I did slow down for a full tank, but like I said, maybe only 3-4 mph. I usually set the CC at 1900 RPM (nets ~73 mph) so that thank I set it at 1800 RPM (~69-70 mph) and didn't see much. The speed limit is 70, but in all honesty, on that highway, that is almost the minimum lest you get your butt run over. Typical speeds on that road are 80-85. It is a large relatively empty bypass well south of Nashville. So 70 is about as low as I want to go. I already get passed like I am standing still at that speed.

 

[JetMechPilot]

There is a 25* limit between the airbox temp and IATs, once your passing that temp, the fan clutch will engage and mpg suffers. You can eliminate it in custom tuning.

What muffler is where the cat was?

Since your in rolling hills take that up hill suggestion i had and also drop speed to 65 as grunt suggested. Your losing mpg on the uphill sides as would be expected, holding throttle works better going uphill.

Can I leave the fan unplugged all the time or only in the winter and not towing?

I will let you know on the muffler.

I will try the CC thing.

Any advice on the transmission though?

Thanks!

 

[steve05ram360]

You can leave the fan unplugged as long as your not overheating the tranny, monitoring the obd port is a must IMO. Take another look at the pics i posted, i will leave that setup as is until my fans cannot keep up with CTs, then pull half that outer cover off and replace the CAC blanket with something that will allow airflow. Currently there is zero airflow thru there, my fans do all the work.... On low speed only. I strive for 200-205* CTs and 100* IATs.

Again for comparison, my old setup doing 70 would get me low 17s, 65 would be closer to low 18s. At your speeds you may not have a lot of room to improve.

200* tstat, 200* CTs and 80*+ IATs will get you good mpgs. But hou have to monitor the port, otherwise you have no idea whats going on.

Re trans... Yeah delete it :grin2. The AT was the one thing i hated about my truck, now that its been gone for 160k miles life us much happier with my truck. Love it more since the swap, even at 387000 miles.
You should get input from the auto trans experts.

 

[steve05ram360]

Gauges... this is using Torque plus a scantool.net MX bluetooth scantool...

if you look to the left and note the air temp & intake temp, those are the 2 that you would get the fan clutch engaged if >25*... unplugging the clutch and it'll never engage. You could always wire up a switch to it and manually control it if needed.

 

[rghavana]

Can I leave the fan unplugged all the time or only in the winter and not towing?



Any advice on the transmission though?

Thanks!

I would not should have winter front end cover on truck, adjust accordingly.

Trans is known issue, stock converter very inefficient, Good aftermarket converter / properly modified valve body, ie Superior kit if want to do yourself or Goerend, or Dynamic built to address pressures/lube/shift issues.

Only way to diagnose trans issues is road test tracking temps/pressures.
Monitor pressures, I used OTC kit inexpensive poor quality gauges but did job https://www.tooltopia.com/otc-tools...MI_5u55InF3wIV1gOGCh0ZxA5eEAQYASABEgJj0PD_BwE
See if pressures are what they should be.
Need add on sensor/gauge either clamp or tap into line for monitoring temps convertor output line, can use monitoring temp sensor in pressure transducer assuming it is functioning properly, have obd reader to monitor, see if excessive heat, clutch/band slippage, other issue by monitoring locked and unlocked converter , and VB trans temp.

Bands/fluid/filter are maintenance item should be done.
130k quick visual front band adjuster position should be above lock nut if not need to check linkage and drop Valve Body, how much lining left on band, can throw in slip in band for front but usually days are numbered for other clutches at that point, for rear band need to drop pan to check/adjust.
Trans info, pressure, overhaul, available in ATSG or FSM, available "newbies guide" if you search for it here.:wink2: