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6.6 Gas MPG

brendon444
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kenny_r
kenny_r

The one thing they got right though is putting the large fuel tanks on the 6.0 HD’s because I’d hate to fill up every 80 miles [emoji23]

i82much
i82much

have you ever heard of the “Internet?”

Cowpie
Cowpie

Yeah, I am really surprised that GM felt the need to depart from 4.10. It might be from a mpg mindset, but usually that doesn't play out as neat as the folks in cubicles think they will.   

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SierraHD17 Senior Enthusiast

SierraHD17

Posted
Posted (edited)
9 hours ago, brendon444 said:

My experience is with the 06-13 trucks. Mine were all in that year. dependable but not great on fuel lol. 

Meh.  I have a 2013 max trailer 6.2 half ton... its leveled with 33" tires.  For fun... it gets the same mileage as my 2017 3/4 ton does lol.. This particular 2017 got really good mileage stock.  17 to 18 mpg highway was no problem when it sat stock rude height, stock tires and its lovely 3.73 fleet order only gears in it.  I have to say I drive a 4 cylinder Malibu when I feel like getting actual good gas mileage.... the fuel savings from parking the trucks buy the car and pay all its expenses plus profit..

 

In the next few months since I work amongst large fleets we will have a bunch of these 6.6 trucks running around being used for what they are designed for... fleet use.  It won't surprise me when they get similar mileage to their outgoing 6 liter counterpart.  

Edited by SierraHD17
Cowpie Senior Enthusiast

Cowpie

Posted
Posted (edited)
On 9/9/2019 at 7:01 AM, brendon444 said:

I’m sure that’s in perfect conditions. Reality is the 6.0 gets bad mileage. I’ve had 7 of them up to 2014. 

 

Might squeeze 14 on highway but usually 12 average 

 

When on regular fuel, I typically averaged 14 MPG (all miles) with my 2015 2500 6.0.  On a couple of road trips, it came in at 17-18 mpg for the trip.  It is exclusively on E85 fuel now for other reasons and so the MPG is lower, but it still averages about 11-12 MPG (all miles) and around 14 for road trips. And considering the substantially lower cost of E85, even with the lower MPG it is still cheaper cost per mile.

 

It might not be the powerhouse that the new 6.6L is, but it is more than up to the task for what I need it for and it is also FF capable, which the 6.6 is not.  So I will hold onto my 2015 for some time yet. It only has 38K miles on it thus far.  I have to let the new front pickup style settle in for a while also.  I really am not a fan of what GM did cosmetically.  But then, I have had a tough time swallowing the design changes since I had my '98 2500.  That was the last one that I really liked the look of.

Edited by Cowpie
KARNUT Senior Enthusiast

KARNUT

Posted
Posted

I’m really surprised at the dropping of factory E-85 vehicles. Years ago even in Texas I saw that in some cities had to run alt fuels. The had big tanks in the bed of their pickups. The conversion isn’t cheap. E-85 use couldn’t be easier.


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cmysstailights Enthusiast

cmysstailights

Posted
Posted
I’m really surprised at the dropping of factory E-85 vehicles. Years ago even in Texas I saw that in some cities had to run alt fuels. The had big tanks in the bed of their pickups. The conversion isn’t cheap. E-85 use couldn’t be easier.


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If it was e85 then i would have thought about upgrading. Now that its not i will wait save my pennies and get a diesel in a few years

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Cowpie Senior Enthusiast

Cowpie

Posted
Posted

There at two things other than cosmetic appearances that really cause me to not consider the new 2020 6.6 gasser 2500.  No flex fuel capability and no 4.10 ratio option.   I have never seen a situation in the last 50 years that a 4.10 ratio option in a pickup truck was not a good thing.   There is only a 400 RPM difference in the top end between the max performance of the 6.6L L8T vs the 6.0 L96.  Even now with my 6.0 with 4.10 ratio, there are many instances where I keep it in manual mode and keep it out of the top gear for better results.  This will be even more pronounced with a 3.73 ratio that the new 6.6 2500 has.    There are myriads of examples form previous 2500's where 3.73 delivered lackluster performance compared to the 4.10, especially in rolling hills when towing heavy.    From what I have seen from the official SAE HP/Torque charts on the L8T 6.6, the best overall engine performance and satisfaction is going to still come by keeping the engine above 2000 RPM on anything other than totally flat roads and no winds without towing, just like the L96 6.0.

 

 

  • 1 month later...
i82much Enthusiast

i82much

Posted
Posted
22 minutes ago, Ky Belser said:

Why do these discussions ALWAYS degenerate into something completely different from the initial question ? ( ie Miles per gallon for a 2020 6.6 gas engine)

have you ever heard of the “Internet?”

  • Like 3
ShotgunZ71 Senior Enthusiast

ShotgunZ71

Posted
Posted

Took the 5er on another trip this weekend. Rural roads, 60 miles away. Averaged 7.6 mpg on that trip. Average speed was about 60 mph, so no doubt that was the biggest factor vs running interstate speeds.

L86 All Terrain Senior Enthusiast

L86 All Terrain

Posted
Posted

Call me crazy but adding 50hp and 80lb-ft of torque, then downgrading the axle from a 4.10 to a 3.73 is effectively the same powertrain as before in terms of performance and consumption. 

 

I get about 12mpg with my 6L, I wouldn't expect more than a 0.5mpg gain with this new set up, probably doesn't feel anymore powerful than the 6L either with the re-gear. Time will tell, I will probably buy a new one and hand mine down next year when they aren't full price, already down to mid 40's in Canada for a 2020 3500 CCSB. Pretty crazy when they want $75,000 for a AT4 half ton. 

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  • 2 weeks later...
texasnavy05 Enthusiast

texasnavy05

Posted
Posted

Update after I've got a few more miles on my 2500 LT 4x4 crew cab gasser.  I've got about 2500 miles on my truck so far.  Here is the MPG from my last 3 fillups.  Note, that these are all with zero trailers, and no added weight other than passengers.

 

12.9 MPG.  This is my best tank average so far.  This was 95% highway driving with cruise set for 70mph about 60% and cruise set at 60mph about 35%.  There were some points where my DIC was reading 15-17mpg over a 25 mile trip.  I really took it easy on this trip and kept my foot out of it to see what the best fuel mileage potential I had.

 

12.1 MPG This was from a mixture of about 60% highway to 40% in town.  Drove normally, not heavy foot, but not babying it.  

 

11.9MPG This was also about 60% hwy to 40% town but with a few mornings of warming the truck up, and a few times where i idled for a little bit.  

 

These are just from my last 3 fill up receipts.  And, for the record my trip mpg display has been about .5-.8 mpg higher than hand calculating.  I'm thinking that 90% of my tanks will be right at the 12mpg.  

 

I've got 285/65r20 ridge grapplers which are .5 inches bigger than stock, so maybe theyre causing the difference.   I'm just not getting anywhere near the numbers that people are posting on here (13-14 in town, and 17 highway).  

  • Like 1
MORSNO Enthusiast

MORSNO

Posted
Posted
1 hour ago, texasnavy05 said:

   I'm just not getting anywhere near the numbers that people are posting on here (13-14 in town, and 17 highway).  

Because you are being honest and not just selecting one good short run, thank you sir!

  • Like 2
Cowpie Senior Enthusiast

Cowpie

Posted
Posted (edited)

Yeah, I am really surprised that GM felt the need to depart from 4.10. It might be from a mpg mindset, but usually that doesn't play out as neat as the folks in cubicles think they will. 

 

12 mpg is really lame.  I do that well running E85 in my 6.0L.  When I have done road trips using E85 exclusively, I have gotten 13-14 mpg with 95% highway.  The newly designed 6.6 running E10 should get that on a bad day.  On road trips with my 6.0 running regular E10, it has averaged 17-18 mpg with 95% highway.  I may not expect the 6.6 to get better than that, but with its new design and direct injection, it should at least match it.  Heck, on road trips I could get 16 mpg with my '98 2500 454.  

 

There must be something we are missing here for the new 6.6 to get such lousy mpg.  While it is a different motor than the 6.0, from what I have seen of the HP / Torque graphs on the motor, some similarities remain.  Just like the 6.0, it doesn't reach 90% of torque until about 2100-2200 RPM.  So if the 3.73 is keeping the engine RPM's significantly lower at road speed, it is taking more fuel to overcome rotational inertia and fuel economy suffers.  Just lessons learned from running commercial heavy trucks for several decades.  

 

I have a spread sheet that I use to calculate road speeds based on tire rotation, trans gear ratios, and diff ratios.  From what I can tell, and assuming the 6 spd in the 2020 2500 has the same gear ratios as the 6L90, with 3.73 and stock rubber on 18" rims (about 32.8 tire diameter / 637 revs per mile), the rpm's would only be about 1850 at 70 mph.  If running taller rubber, the RPM's drop even more.  So much so that the RPM's are way outside the optimum range to be efficient.   It is taking more fuel to keep things moving.  The motor is essentially lugging the truck along.

 

I did a calc using 285/65R20 which are 34.5" with 602 revs per mile.   RPMs' would be about 1750 at 70 mph.   That is going to really be terrible for fuel economy.  The engine is having to really suck fuel at that low of RPM to keep things moving.  Overcoming rotational inertia is killing fuel economy.  Whereas with 4.10 ratio, the RPM's would be around 1950 at 70 mph.  A lot closer to the optimum of the motor but not quite there.  So the 34.5" rubber is having a negative affect for sure. And tied with 3.73 the results are terrible.

 

Cliff

Edited by Cowpie
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texasnavy05 Enthusiast

texasnavy05

Posted
Posted
Yeah, I am really surprised that GM felt the need to depart from 4.10. It might be from a mpg mindset, but usually that doesn't play out as neat as the folks in cubicles think they will. 
 
12 mpg is really lame.  I do that well running E85 in my 6.0L.  When I have done road trips using E85 exclusively, I have gotten 13-14 mpg with 95% highway.  The newly designed 6.6 running E10 should get that on a bad day.  On road trips with my 6.0 running regular E10, it has averaged 17-18 mpg with 95% highway.  I may not expect the 6.6 to get better than that, but with its new design and direct injection, it should at least match it.  Heck, on road trips I could get 16 mpg with my '98 2500 454.  
 
There must be something we are missing here for the new 6.6 to get such lousy mpg.  While it is a different motor than the 6.0, from what I have seen of the HP / Torque graphs on the motor, some similarities remain.  Just like the 6.0, it doesn't reach 90% of torque until about 2100-2200 RPM.  So if the 3.73 is keeping the engine RPM's significantly lower at road speed, it is taking more fuel to overcome rotational inertia and fuel economy suffers.  Just lessons learned from running commercial heavy trucks for several decades.  
 
I have a spread sheet that I use to calculate road speeds based on tire rotation, trans gear ratios, and diff ratios.  From what I can tell, and assuming the 6 spd in the 2020 2500 has the same gear ratios as the 6L90, with 3.73 and stock rubber on 18" rims (about 32.8 tire diameter / 637 revs per mile), the rpm's would only be about 1850 at 70 mph.  If running taller rubber, the RPM's drop even more.  So much so that the RPM's are way outside the optimum range to be efficient.   It is taking more fuel to keep things moving.  The motor is essentially lugging the truck along.
 
I did a calc using 285/65R20 which are 34.5" with 602 revs per mile.   RPMs' would be about 1750 at 70 mph.   That is going to really be terrible for fuel economy.  The engine is having to really suck fuel at that low of RPM to keep things moving.  Overcoming rotational inertia is killing fuel economy.  Whereas with 4.10 ratio, the RPM's would be around 1950 at 70 mph.  A lot closer to the optimum of the motor but not quite there.  So the 34.5" rubber is having a negative affect for sure. And tied with 3.73 the results are terrible.
 
Cliff
I wonder what fuel mileage would look like if I kept it out of overdrive.

I've noticed that it does stay at lower rpms at hwy speeds.

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