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V8 gas mileage?

ecobos27

New member
I own a 2021 Grand Cherokee L Limited. I am getting 16.9 mpg combined about 5000 miles. Mostly city driving with some hwy. It’s seemed to have gone up from 13 mpg. At first I thought the cars computer might be tracking the miles wrong. So I filled the tank drove 20 miles and filled the tank again and did the math and it was right 16.9 same as the car was marking. My wife drives it. She keeps it in auto and she doesn’t have a heavy foot.
 

Deere78

Well-known member
I own a 2021 Grand Cherokee L Limited. I am getting 16.9 mpg combined about 5000 miles. Mostly city driving with some hwy. It’s seemed to have gone up from 13 mpg. At first I thought the cars computer might be tracking the miles wrong. So I filled the tank drove 20 miles and filled the tank again and did the math and it was right 16.9 same as the car was marking. My wife drives it. She keeps it in auto and she doesn’t have a heavy foot.
It’s very disappointing. Had I known this was the mileage we would get I would not have even considered this vehicle. The 2020 explorer we had previous was averaging 23-24 combined.
 

nealtrombley

Well-known member
all you folks using 89 or better octane.. 93?
My denali with 6.2 runs so much better with 93... I tried the 87 since gas hike.. went back to 93
 

RichSNJ

Well-known member
While I haven't actually done an actual mileage tracking calculation, I pretty much have figured out why Auto Start Stop exists and why the V8's mileage is reported as so low. I don't understand why they do it this way, but it appears that when you are idling, it counts as a constant value of "0 mpg" which gets added to your mpg average totals. I can only assume that the EPA requires auto makers to do this, which is why the auto stop really would make a significant difference in reporting, but not really in actual mileage.

I figured this out because I was curious as to why I would be driving down the road in 4 cylinder mode and I would consistently see mpg's around 24mpg on a level road, but my average mpg was so low, so I decided to reset the mpg and test it out. I was driving down the road with an average of 24 mpg, and then I stopped a light and my average mpg was falling down very quickly right in front of my eyes. So, basically every time you remote start your car, or sit at a light, or are stuck in traffic, your average mpg is going down dramatically. For somebody like me who doesn't do a lot of long distance driving, this makes a big difference in what the average mpg gets calculated to. So many experts I have seen have said that the auto stop really doesn't save much, but when you stop all of the idling counting as 0's, you can see where it would make a big difference, at least in what the car is reporting to you.

I don't agree with this methodology of using the 0 figures in the average calculation. While it's true that yes your engine is running and you're getting 0 miles for it, it is not a fair rating of what kind of mileage the engine is capable of delivering. Every gas engine regardless of efficiency is going to get 0 mpg when it's not moving, so I feel that it would be more useful for the car to simply delete 0 entries from its average ratings so that you'd get an average of mpg based on the engine actually doing what it's supposed to be doing. I now no longer give a crap about what the car is reporting as average mpg because I know it's not right.

Eventually I'll take a road trip and calculate my mileage and see how it goes, but until I do I'm not going to regret my hemi, especially when I'm merging into traffic...
 

dseffren

Well-known member
After approximately 1200 miles I have observed the following:

City = 14.7 - 15.5 mpg
Hwy = 20.2 - 21.5 mpg

The vehicle is still pretty damn new, but the numbers are not terrible considering. Our '21 JGC WK2 is getting 17.5 in the city and around 22.5-23.0 on the highway. I don't know why people are so alarmed by a 360hp V8 getting mileage in the teens?

Now, I did see better mileage in my '21 BMW X5 M50i with a twin-turbo V8, but I was so busy hammering the gas on that so I very rarely got a tank where I saw better than mid to low teens in the city.
 

Deere78

Well-known member
After approximately 1200 miles I have observed the following:

City = 14.7 - 15.5 mpg
Hwy = 20.2 - 21.5 mpg

The vehicle is still pretty damn new, but the numbers are not terrible considering. Our '21 JGC WK2 is getting 17.5 in the city and around 22.5-23.0 on the highway. I don't know why people are so alarmed by a 360hp V8 getting mileage in the teens?

Now, I did see better mileage in my '21 BMW X5 M50i with a twin-turbo V8, but I was so busy hammering the gas on that so I very rarely got a tank where I saw better than mid to low teens in the city.
My issue is the v6 was rated higher than what we are experiencing. Our outgoing vehicle was a 2020 explorer and it got the advertised mileage or sometimes even more than the sticker said if you were conservative on the go pedal.
 

Obspoint

New member
GCL SR 5.7L V8 on five months of ownership over 6,800 miles of flat, Midwest streets, highways, and interstates 700-900 feet above sea level. One oil change, filled with Costco 93 octane when home, BP / Shell 89 octane on road trips.

City driving (suburban mix of 25mph neighborhoods surrounded by 35-50mph highways) returns 10.2-10.7mpg
One Florida 2,500+ mile interstate road trip with adaptive cruise set between 65-80 returned 18.2mpg

This past weekend we followed a large class C RV in the right lane for 150+ miles at 68mph with adaptive cruise set to the closest following distance. It returned 22.8mpg, the only time this car reached it's EPA highway number. We've never seen anything close to the EPA number in city conditions. The return trip with normal traffic in the middle lanes returned low 18s again.

I have no regret about the V8 purchase, but would like the EPA to get it together. This isn't the first time they've been 30-40% higher than real world figures and needed to adjust.
 

Sarge

Well-known member
Assuming I won't get my lemon replaced with a turbo I6 soon, I'll be trading my replacement Hemi for a '24 as soon as that I6 turbo is available (provided the 525hp version quits itself reliably in the Wagoneer). I thought my Hemi would hit its EPA numbers in my general driving around home (my other cars do), but it's still been a steady 13-14-15 mpg avg over the last 8500 miles on 89 octane. I thought it might improve after 5k miles, but no.
 

tjw68

Member
At 38,000 miles, I'm averaging 17.96 mpg on 87 octane fuel.
Mostly metro area driving.
The mpg reported by the vehicle is garbage, well below actual.
You need to calculate total-miles-on-vehicle / total-gallons-consumed.
Otherwise you're just guessing.
 

tjw68

Member
I haven't seen any buttons for 'eco mode' or any dash indications. How would I know?
There's no button. The engine automatically goes into 4-cylinder mode when conditions allow. If you're showing screen 2 in your dash, "4-cyl" will appear above your fuel economy number when it comes on. You won't really feel any change when it kicks in or off.
 

RichSNJ

Well-known member
At 38,000 miles, I'm averaging 17.96 mpg on 87 octane fuel.
Mostly metro area driving.
The mpg reported by the vehicle is garbage, well below actual.
You need to calculate total-miles-on-vehicle / total-gallons-consumed.
Otherwise you're just guessing.

I posted a comment somewhere a few months back regarding this, maybe in this thread... Whenever you are at idle, the computer records 0's into the running average of mpg, I discovered and tested this out on a whim one night, so anybody who idles significantly, or remote starts on a regular basis, is going to get an artificially low mpg reported by the computer. I stopped caring about the reported mpg that night.
 

Sarge

Well-known member
I've calculated mine from the pump numbers against the odometer, and it's the same. You're still using gas at idle, and I believe it is calculating fuel flow from the injectors and measuring it against the odometer. It's definitely not using the fuel gauge; Mine doesn't even move off the full mark for the first 100 miles...
 

RichSNJ

Well-known member
I've calculated mine from the pump numbers against the odometer, and it's the same. You're still using gas at idle, and I believe it is calculating fuel flow from the injectors and measuring it against the odometer. It's definitely not using the fuel gauge; Mine doesn't even move off the full mark for the first 100 miles...
It's my understanding that you use very little fuel at idle. The night that I discovered this I had just driven several miles in 4 cyl mode and was averaging 24 mpg by the computer, sitting at idle for one traffic stop, I watched the number go down to under 14 very quickly in front of my eyes. My only way to explain this is that they are giving 0's equal weight in the averages to actual fuel usage numbers. Some may agree with your argument that "You're still using gas at idle", but imho I don't believe that this is a fair representation of the actual mpg that the engine is capable of. I remote start every single day, sometimes several times a day, I want to see the actual mpg that it attains while being used to move me, not while it's sitting in my garage warming up.

But you say you've done the calculations, and I believe you, so someday soon I'll have to do a trip and do my own calculations so I can see what the numbers actually are.
 

Sarge

Well-known member
There are separate trip computers you can set that will calculate mileage over the life of the 'trip'. I think that's more accurate, as the main display on the dash is sort of a 'rolling recent' display, that seems to reduce the weight of older 'miles' and must be averaging over the last 50 miles or maybe less, I'm not sure.

But, I'd say check your 'trip computer' mileage between fill ups and see how that compares to the 'running average' in the main display, as the latter is heavily weighted on recent performance.

With mine, it's kind of all the same anyway. I was really hoping for a PHEV I6 turbo, and might even consider the 4xe drivetrain if it were available in the three row. As it is, though, I lose about 30% of the naturally aspirated power at my elevation, so my V8 is basically the same HP as the V6 (~290hp), but the V6 would only make a bit over 200hp at my elevation, which won't work for towing in the mountains at all. A 4XE would blow the doors off my Hemi at 6500' elevation, and I'd probably run in electric-only mode for most of my driving. Meanwhile... I get 14mpg and 290hp 🤦‍♂️
 

RichSNJ

Well-known member
There are separate trip computers you can set that will calculate mileage over the life of the 'trip'. I think that's more accurate, as the main display on the dash is sort of a 'rolling recent' display, that seems to reduce the weight of older 'miles' and must be averaging over the last 50 miles or maybe less, I'm not sure.

But, I'd say check your 'trip computer' mileage between fill ups and see how that compares to the 'running average' in the main display, as the latter is heavily weighted on recent performance.

With mine, it's kind of all the same anyway. I was really hoping for a PHEV I6 turbo, and might even consider the 4xe drivetrain if it were available in the three row. As it is, though, I lose about 30% of the naturally aspirated power at my elevation, so my V8 is basically the same HP as the V6 (~290hp), but the V6 would only make a bit over 200hp at my elevation, which won't work for towing in the mountains at all. A 4XE would blow the doors off my Hemi at 6500' elevation, and I'd probably run in electric-only mode for most of my driving. Meanwhile... I get 14mpg and 290hp 🤦‍♂️

I wouldn't be so quick to jump into the new engine... While I agree it sounds good on paper, I would suspect they'll have a lot of issues with it for the first few years, and who knows how reliable it will be after several years. I don't know about you, but the amount of $$ I sunk into my GCL kind of makes it the last SUV I want to purchase...

I've never driven at elevation other than to drive up Pike's Peak in a rental car, so I don't really know what happens to an engine at altitude. Do you think that your high altitude is affecting your gas mileage as well?

I know you've had all sorts of issues with your GCL, but maybe a better solution for you since you're at altitude would be to look into an after market super charger for the 5.7, I'm sure there's got to be a ton of them available.
 

Sarge

Well-known member
I wouldn't be so quick to jump into the new engine... While I agree it sounds good on paper, I would suspect they'll have a lot of issues with it for the first few years, and who knows how reliable it will be after several years. I don't know about you, but the amount of $$ I sunk into my GCL kind of makes it the last SUV I want to purchase...

I've never driven at elevation other than to drive up Pike's Peak in a rental car, so I don't really know what happens to an engine at altitude. Do you think that your high altitude is affecting your gas mileage as well?

I know you've had all sorts of issues with your GCL, but maybe a better solution for you since you're at altitude would be to look into an after market super charger for the 5.7, I'm sure there's got to be a ton of them available.
I'd rather keep my factory warranty in tact given how problematic these things are. I also have an extended warranty (and will on my replacememt). I'm anticipating the value of my '23 MY Hemi replacement will be pretty high when the I6 comes out (projected for '24 MY) as many people won't want the unproven engine. I figure the worst case is the new motor has lots of problems and it goes in under the lemon law, or if it makes it beyond the lemon period I'll have an extended warranty, and hopefully they'll have solved a lot of these electrical issues by then.

For me, the increase in power (an extra 135hp!) is worth the risk, along with better fuel economy and the inherently balanced nature of an inline 6 make that motor ideal. They've been developing it for years, so hopefully it will be good out of the gate.

At altitude, there is less oxygen in the air. Naturally aspirated motors have to dial back the amount of fuel they deliver because there isn't enough air to make a 'sea level' size explosion. Superchargers help, but are constrained by the fat that they're driven by a pulley (you can install a smaller pulley to compensate, but you could then blow your motor potentially at sea level. Turbos, on the other hand, just keep spinning higher as the ECU requests MORE AIR! so the constraints are limited to the size/capacity of the turbos, and modern turbo systems adjust with elevation. There's also no parasitic loss as there is with a pulley-driven supercharger. Some companies are now offering electric superchargers, which addressees that issue, but I'd still prefer turbos, as they're driven by the exhaust.

If you don't modify your stock setup for more boost, modern turbos are also very reliable if designed correctly (my wife's stock 2008. 535xi wagon still pulls like a new car at 160k+ miles).

So, yeah... the new turbo I6 would be ideal, for me anyway, and the risks are mitigated by the warranty. I'll be watching the Grand Wagoneer forums when they start delivering the 525jp version in that car, though. It's basically a boosted version of the same 3.0L motor, with stronger internals and bigger turbos.
 
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