Jump to content

Sudden Fuel Mileage Drop


Recommended Posts

2018 1500 5.3 CCSB with max trailering 3.42 gears all stock except for DOD disabler in obd2 port.

I drove 1,400 miles over the holidays through the mountains into NYC area with loads of traffic. Got 19.7 over the entire trip according to the dash calculator. It averages 22-24 on trips to and from work and around town/backroads. Pretty good for a full size/v8 with towing gears in my opinion.

 

Today that all went out the window. I did the sure-cool trans cooler mod install, a 1" front spacer level and tuned it with a diablosport i3 mpg booster and permanently disabled DOD.

My mileage has dropped to 18-19 on the same routes I take that I used to get 22-24. What could of caused this? 

1. Could a 1" lift really cause that much aerodynamic drag?
2. Is it the 1" lift causing a mis-alignment and the tires dragging on the pavement a touch more? I haven't had an alignment done yet that comes early next week.
3. The trans temp only got to 104 with the sure-cool because temps have been really cold today/tonight. Is this causing it?

4. Maybe the mpg booster tune isn't as good as it says it is. The truck drives and feels significantly better with the tune installed though.

5. Maybe it' a combo of each mod causing a little fuel mileage decrease each and it adds up?

6. Do these tunes "settle in" once it figures out all the trims?

7. I don't know if it's just me thinking about it more but it does feel like the truck doesn't glide as much when I'm off throttle and not on the brakes.

 

Edited by scralatchtica824
  • Like 1
Link to comment
Share on other sites

Number 5.  Yes, the lift will have an effect, the cooler transmission temps possibly some, the tune.  If you want o measure performance, make only one change at a time.  You have three things done at once and performance has suffered.  

 

So the easy thing to do is undo the tune and test.

  • Like 2
Link to comment
Share on other sites

Ambient temps were also much colder in the NYC area this past weekend, which definitely has an impact for a multitude of reasons. 
 

Without touching anything on the truck, run another tank to get more objective data. One data point does not a trend line make. That said, every mod you’ve made decreases fuel economy. 

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

A few weekends ago I made a trip up north to the cabin, it was -15F outside for most of the day and I struggled to get 17-18mpg in that temp, where as I can get over 21-22 in the summer.

 

The temp and level are surely a cause for a minor drop but how much is tough to say for sure.

Link to comment
Share on other sites

22 hours ago, scralatchtica824 said:

2018 1500 5.3 CCSB with max trailering 3.42 gears all stock except for DOD disabler in obd2 port.

1. Could a 1" lift really cause that much aerodynamic drag?

 

Entirely possible but not to that extent.  .5mpg loss, maybe 1?


2. Is it the 1" lift causing a mis-alignment and the tires dragging on the pavement a touch more? I haven't had an alignment done yet that comes early next week.

 

This could be a contributor.  As you raise the front, you toe in and that would increase rolling resistance.


3. The trans temp only got to 104 with the sure-cool because temps have been really cold today/tonight. Is this causing it?

 

This is a possibility as well and possibly a top contributor.  Higher trans temps would allow for less friction in the gearbox.  The ideal move would be the new lower temp GM thermostat, that way it gets warmer in the colder weather, but with its 158F opening temp, still runs cooler in the warmer seasons.

  

4. Maybe the mpg booster tune isn't as good as it says it is. The truck drives and feels significantly better with the tune installed though.

 

I have no experience with handhelds, only custom tunes.  On my truck with custom dyno tuning, my mileage has been .5mpg compared to stock with a Range DOD.  

 

5. Maybe it' a combo of each mod causing a little fuel mileage decrease each and it adds up?

 

Yes.  I'd start with flashing it back to stock and re-test.  If you see no change, get the GM updated thermostat for the transmission and re-test.  

 

 

  • Like 1
Link to comment
Share on other sites

Truck dropped off for alignment. I'll report back. Haven't made any other changes... yet... I wasn't doing this mod's to necessarily increase mileage... obviously. But the huge hit was surprising. I'll make changes 1 at time from here on out to expose the culprit! Apparently even small lifts cause major issues with alignment specs mainly toe in until they are rectified with an alignment rack and some wrenches. Time will tell!

  • Like 2
Link to comment
Share on other sites

5 minutes ago, scralatchtica824 said:

Truck dropped off for alignment. I'll report back. Haven't made any other changes... yet... I wasn't doing this mod's to necessarily increase mileage... obviously. But the huge hit was surprising. I'll make changes 1 at time from here on out to expose the culprit! Apparently even small lifts cause major issues with alignment specs mainly toe in until they are rectified with an alignment rack and some wrenches. Time will tell!

 

5 minutes ago, scralatchtica824 said:

Truck dropped off for alignment. I'll report back. Haven't made any other changes... yet... I wasn't doing this mod's to necessarily increase mileage... obviously. But the huge hit was surprising. I'll make changes 1 at time from here on out to expose the culprit! Apparently even small lifts cause major issues with alignment specs mainly toe in until they are rectified with an alignment rack and some wrenches. Time will tell!

 

 

 

 I can understand why you are concerned about fuel mileage, but the drop seems to be nominal. To me, fuel mileage means nothing unless its extreme. Like if my mileage cut in half, I would probably take notice, but a few MPG's? Meh - I spend as much money on steaks at the grocery store as I do gasoline. So if for some reason I want to save money, I would probably start with my food budget. But that's just me.

 

 

bf5aa5a4dc853e113209e51e7d6964e826399415

  • Haha 2
Link to comment
Share on other sites

19 minutes ago, Supreme Pizza said:

 

 

 

 

 I can understand why you are concerned about fuel mileage, but the drop seems to be nominal. To me, fuel mileage means nothing unless its extreme. Like if my mileage cut in half, I would probably take notice, but a few MPG's? Meh - I spend as much money on steaks at the grocery store as I do gasoline. So if for some reason I want to save money, I would probably start with my food budget. But that's just me.

 

 

bf5aa5a4dc853e113209e51e7d6964e826399415

Oh I totally understand your point of view, and I'm seeing the same sunset as you are. My main concern is the "drag" as the truck feels heavy. Prior it would glide effortless in fact it would gain speed on the highway with any downhill grade. Now it feels like a caliper is dragging. I'm fairly confident it's the mis-alignment causing most of the slow and heavy feeling. I wouldn't of purchased a v8 that weighs 5,500lb's if I wanted great mpg LOL

Edited by scralatchtica824
  • Like 2
Link to comment
Share on other sites

13 minutes ago, scralatchtica824 said:

I'm fairly confident it's the mis-alignment causing most of the slow and heavy feeling.

 

Somewhere in my build thread I found that my factory 'in spec' alignment while in spec was all over the map within those specs. When I fixed that...WOW!! Largest single gain in mileage from any one enhancement. Worth ever penny I spent so now I check it about once a year and keep it perfect. 

  • Like 2
Link to comment
Share on other sites

23 minutes ago, Grumpy Bear said:

 

Somewhere in my build thread I found that my factory 'in spec' alignment while in spec was all over the map within those specs. When I fixed that...WOW!! Largest single gain in mileage from any one enhancement. Worth ever penny I spent so now I check it about once a year and keep it perfect. 

 

 

I have looked into alignment shops, as I need to have one done after a 2.5" spacer lift front and rear. Firestone offers a one time and a lifetime alignment option. The last time I went there, they rounded off the threads on my tie rod end threads - using a pair of vice grips maybe? I was not happy with the damage. They offered no compensation. Who has the best deal on alignments?

  • Like 1
Link to comment
Share on other sites

I’ve never had an alignment done ever. My wife’s car gets the same mileage after 10 years. My trucks off road never. My tires would run 90K miles. I ran KOs highest ply I could buy. People are really paranoid or have real bad roads. Maybe drive too fast on bad roads. Almost 50 years driving, really no alignments. I don’t get it.

  • Like 1
Link to comment
Share on other sites

26 minutes ago, KARNUT said:

I’ve never had an alignment done ever. My wife’s car gets the same mileage after 10 years. My trucks off road never. My tires would run 90K miles. I ran KOs highest ply I could buy. People are really paranoid or have real bad roads. Maybe drive too fast on bad roads. Almost 50 years driving, really no alignments. I don’t get it.

 

 

I hear ya.

 

In theory, as long as the alignment is set at the factory - and there are no major front end repairs or damage, then the alignment should be fine for ever.

 

After major front end repairs, I used to do the alignment myself, using a tape measure and hand tools.

 

Now I just take it in and have it done, but only if its justifiable.

 

For most, the annual alignments are a complete waste of money. But if you NEED one, then you NEED one.

  • Like 2
Link to comment
Share on other sites

1 hour ago, Supreme Pizza said:

 

 

I have looked into alignment shops, as I need to have one done after a 2.5" spacer lift front and rear. Firestone offers a one time and a lifetime alignment option. The last time I went there, they rounded off the threads on my tie rod end threads - using a pair of vice grips maybe? I was not happy with the damage. They offered no compensation. Who has the best deal on alignments?

 

I use a small volume private shop with an owner I have developed a personal relationship with.

I don't think this is chain store service when you get as picky as I do.

 

This was my OEM factory alignment. 

So much for, "It leaves the factory perfect".

 

post-161433-0-91552300-1490407962_thumb.jpg

 

This is the job Deegan's did shortly after I bought it. 

2+ MPG difference.

post-161433-0-65318600-1490405985_thumb.jpg

 

This is the alignment after the Bell/King/Deaver upgrades.

Thrust angle on this one was ZERO as was steer ahead. 

 

Added over 50 yards to the 50 mph coast down distance.

The first check and subsequent adjustments produced 125K miles of tire life on the OEM set

I balance every 10K and rotate every 5K

Check and adjust as needed every time I put my butt in the seat

OEM tires left service with 5/32" left and dead even wear.

They dated out or I would have run them another 25K.

 

KingBellAlignment.thumb.jpg.2093920ab7b6a6f987167a336b94d73b.jpg

 

 

I don't tell people what I think this or that is worth based on my best guess or speculation. 

 I base it on RESULTS I get from the work I do.

I don't guess. I measure, adjust and repair/modify as needed. Collect the data and graph it or photograph it.

 

Tire life was the result of 125K miles of such tweaks.

 

I pay for this work. I reap the results of that work. I share those results AND THE WORK so that others may PROFIT if they choose to. If you're good with 40 to 60K out of tires and doing full suspension rebuilds every 100K or so then ignore the advice. It cost me nothing. In fact it pays me. My gas savings alone pay for my alignment checks and leave enough left over for pizza and beer. I spend less on rotations and balance than the price of a new set of tires given the extra miles I get from them. I have no interest in ROI. Truck isn't a business and I have no board to answer to.  

 

To the OP. Lift, Aggressive larger tires. Alignment. All MPG Killers. Cold oil affects ALL drivelines. Cold is just winter. Not as big a deal as some think. It is viscosity related but not the largest piece of the pie. I've done my best with a good sharp factory tune and careful setup of suspension and lubricant choices. The difference between my lightest to heaviest oils has been about 1.5 mpg. The difference in equipment life based on viscosity can be multiples. I lean heavy and I run colder than most. Just say'n. 

 

 

  • Like 3
  • Thanks 1
Link to comment
Share on other sites

22-24 is unrealistic I don't care what the onboard readout says.  The ONLY sure method to calculate mileage is by logging miles and fuel used over thousands of miles and then averaging it out.  Taking one snapshot in time and using that as gospel is flawed as these in-vehicle average MPG displays are almost always inaccurate..  If those figures were true (22-24mpg) than GM would be claiming that mileage on the window sticker like on this 2022 Silverado equipped similar to yours. 

 

 

 

2022 spacer.png

Edited by elcamino
  • Like 2
  • Thanks 1
Link to comment
Share on other sites

6 hours ago, Supreme Pizza said:

 

 

I hear ya.

 

In theory, as long as the alignment is set at the factory - and there are no major front end repairs or damage, then the alignment should be fine for ever.

 

After major front end repairs, I used to do the alignment myself, using a tape measure and hand tools.

 

Now I just take it in and have it done, but only if its justifiable.

 

For most, the annual alignments are a complete waste of money. But if you NEED one, then you NEED one.

I never had front end work either. Most of my trucks went off road. I didn’t keep my trucks past 3 years 150k miles average. I never put over sized tires on  either. Most had tool boxes and fuel tanks. The first 20 years I ran my equipment one ROWs, pipelines mostly. The second 20 years plus selling equipment and training mostly on pipelines. My last truck a used Avalanche I bought with 167K miles recently had tie rods and shocks. That’s it. 

  • Like 2
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.




×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.