MPG computer lies - badly!

[rrbhokies]

For myself, I can't complain really. Computer says 24+ mpg, so even dropping that down by 3 to 4 mpg if the computer is off, means I'm still probably hitting the rated MPG.

Is your house located on the highway, along with your job and all the stores you go to? The only way I could ever possibly get close to 24mpg is if I was literally driving 55mph on an open highway with a tail wind, and never having to stop. I can't for the life of me think about a day to day scenario where I could average 24+ mpg or even 20+ mpg for that matter.

 

[silver billet]

Is your house located on the highway, along with your job and all the stores you go to? The only way I could ever possibly get close to 24mpg is if I was literally driving 55mph on an open highway with a tail wind, and never having to stop. I can't for the life of me think about a day to day scenario where I could average 24+ mpg or even 20+ mpg for that matter.

I should have been more specific, that particular measurement of 24 mpg was the average for a 4 hour trip including 3 hours of freeway + 1 hour of general rural driving. So I believe I don't have any problem getting the rated highway MPG.

But yes, most of my driving is in 7th or 8th gear.

It's really funny watching people drive on the highway though, it's not a nice thing to say but most people don't deserve to have a license. They're on the gas, then hitting the brakes, then skipping in front of some trucker and then jumping back in front of another car, it's an endless, nervous, psychopathic driving style that is hard on gas, hard on the brakes, and hard on the drivers all around them; they don't care about anything or anybody but themselves.

Often I cruise in the right lane at just above the posted speed, (bonus points for trailing a trucker), I just keep a steady foot, rarely hit the brakes, and slowly accelerate when needed. Cars on the left are driving a little nuts at times, with the odd physocpath skipping about like a rabbit dodging a cat. 20 mins later we hit a traffic jam; all the traffic is stopped and crammed on top of eachother in the left 2 lanes, and we just slowly pass everyone in the right lane which is still moving (slowly, but faster than the guys who are stopped). I end up passing the nut jobs 20 mins after they flew past me, so it doesn't get them anywhere ever, but hey, they're sure trying hard to save 30 seconds on a 30 minute trip.

^^ If you drive like that, don't be surprised when you don't hit the rated MPG!

I mentioned the trucker, because truckers absolute hate having to stop, and they have a nice calming affect on the lane they're in by adding a large buffer which absorbs the fast stop and go situations. Instead of doing 30 - 0 - 30 - 0 - 30... they end up doing 15 for most of the traffic jam with no stops, so I usually pick one of the big guys to follow in a traffic jam and end up keeping my sanity. The only downside is the view!

 

[Gsmith223]

First, this thread is NOT about the absolutely atrocious mileage I'm getting. There are already enough threads on the Hemi's bad mileage.

This is about how the computer that displays my fuel economy is lying. Lying like a rug! Liar, liar, pants on fire!

I've got about 1050 miles on my new truck. I have been tracking the mileage using Fuelly since I filled it up when I first got it home. It had about 220 miles on the clock then, so Fuelly says I have been tracking fuel economy for 813 miles, so far.

Whenever I fill up, I reset Trip B, AND I reset the Fuel Economy display in the EVIC (center dash display).

Yesterday, I filled up after driving 383 miles on the previous fill-up. It took 30.518 gallons. That is 12.55 MPG. But, at the point of filling up, the EVIC Fuel Economy display said I had been getting 14.5. That is a pretty huge discrepancy.

I reset Trip B and the Fuel Economy display when I filled up (as I always do).

After filling up, I immediately got on I-85 and headed north, through Richmond, towards DC. When I got home (after all highway driving), I filled up again, just to check it. I had driven 160 miles and it took 10.890 gallons. That is 14.7 MPG. But, the Fuel Economy display AND the Trip B display both said I had been getting 17.2. Again, a huge discrepancy.

We all know that the exact way you fill up, how level the truck is, etc, etc can affect mileage calculations. But, with these distances and amounts of fuel, the discrepancies that could come from those variables is going to be in the tenths of a mile per gallon - not 2 whole MPG.

Over 813 miles, those discrepancies pretty much wash out. One fill-up might have been a little short, for example. But, the total amount of gas put in is exact, as is the number of miles driven. So, the only 2 variables that affect anything are exactly how full it was at the very start of that 813 miles and exactly how full it was after the very last fill-up.

So, Fuelly says that my average over 813 miles is 13.2 MPG and my best on any one fill-up was 15.8 MPG. All of which is simply to validate the specific "hand calculated" numbers from yesterday. 12.5 for 3/4 city driving and 14.5 for all highway seem completely in line with the overall history.

And the amount of optimism shown in the onboard computer is really disappointing.

I have seen a bunch of posts on here from people talking about getting 20+ MPG with their Hemis. Some of them have explicitly acknowledged that their statements were based on what the on-board computer says. So, uhhh.... yeah. You guys reporting what your on-board computer says may as well save your breath - unless you also hand-calculated and are reporting how the two numbers compare.

Personally, my new truck and my last truck (an '09 4th Gen) are the same - CrewCab, 5'7" bed, 4x4, Hemi (new one has eTorque), bed cover, stock sized tires, and 3.92 rear end. I was really hoping to get a decent bump in fuel economy with the new truck, just because of the 8-speed tranny and the eTorque (and having 193K less miles on it). And the fact that new truck has air suspension and lowers itself at speed where my old truck had coil suspension and actually had a 2" lift/level on it. I THOUGHT, from the on-board computer, that the new truck was doing a little better than the old truck. I am pretty bummed to see that that was all lies. The new truck is definitely doing no better than the old truck and maybe slightly worse.

Its a lot about how you drive and the roads you drive on. My EVIC actually shows worse MPG than hand calculated. I get 21-23 MPG highway and 16 mixed. Yours will get better as it breaks in. Just wondering have you put bigger tires on your truck?

 

[GRAYWOLF]

[QUOTE="the wanderer, post: 166156]The only downside is the view![/QUOTE]

Well...if you aren't the lead dog...blah, blah, blah...

Sent from my SM-G965U using Tapatalk

 

[StuartV]

Its a lot about how you drive and the roads you drive on. My EVIC actually shows worse MPG than hand calculated. I get 21-23 MPG highway and 16 mixed. Yours will get better as it breaks in. Just wondering have you put bigger tires on your truck?

Nope. Stock 22" wheels and tires, at the pressure prescribed on the door jamb sticker (36 psi, IIRC - EVIC says 40 - 42 when rolling and hot).

 

[Cueva del Osos]

We took a 230 mile ‘long way’ home from the dealer last weekend after picking up the new truck and averaged 19.5 mpg. I was keeping it at 50-55 with a few surges higher but trying to be a good boy during the break in period. We have the 26 gal tank and fuel gauge showed just under 5/8ths, so the mpg reported is pretty close for us.

I had a 1.5 mile commute for 20 years and yes, it kills mpg (just pouring it down the injectors) but it also killed my exhaust systems. When you don’t get up to temp, the condensation in the muffler & pipes just rusts it all to sh!t.

As to the question of why we’re so concerned about mileage, I personally am curious about it and like calcing the numbers, but I also like to know what my vehicle will do depending on how I drive. I ‘can’ have a heavy foot, but if I know that move will cost me 3 mpg, I’m much more likely to keep it relaxed and save the race-track simulation for a time I really need to get somewhere fast.

 

[Gsmith223]

Nope. Stock 22" wheels and tires, at the pressure prescribed on the door jamb sticker (36 psi, IIRC - EVIC says 40 - 42 when rolling and hot).

You have something wrong then

 

[Jus Cruisin]

Ok, you all made me look at my MPG readout (L-O-M). Can't remember when I last reset it. 20.4 I highly doubt it's close to 20mpg in reality. I haven't hand calculated the mpg probably since a few weeks into ownership.

 

[StuartV]

You have something wrong then

I'm not so sure. If you look back at the Fuelly log that @GRAYWOLF posted (on page 2 of this thread), it looks like I'm getting about the same as him. My truck IS a fully loaded Laramie CrewCab with 4WD and 3.92 rear end...

 

[BTheez]

When I first got my truck in November I was getting around 13mpg. I had an 8 mile commute with a few hills, all 30-40mph zones and 6 or 7 red lights. If I tried my best to squeeze out good mpg I would get around 15.5 mpg. Upon fill up I would hand calculate and the on board reading was usually always .8 mpg higher than what I actually consumed. Once the engine got a few thousand miles on it I noticed my mpg went up at least 1mpg on average. Now throw in the warm weather and 6k on the motor I'm having a hard time getting less than 15 mpg around town. However, Ive recently taken a few 300 mile trips and my best economy so far was 21.4 mpg highway which included very few hills and a good 40 mins of stop and go traffic. Once out of traffic I was cruising around 85mph and hit 100 a few times out of curiosity (it's super smooth btw) and hardly ever left 8th gear while doing so. I hand calculated that and it was spot on. I would say wait until the engine breaks in and your eco becomes more prevalent. Your mileage will increase in a couple thousand miles for sure. Dont stress it

 

[41magmag41]

my computer mpg is always within .4 of my hand calculations, when I check it every now and then. Its a full size pick up with a 5,7 and 3.92 rearend. what do you want an economy car get one but a truck is a truck.

 

[ColoradoCub]

MPG since new

 

[Jus Cruisin]

MPG since new

You may not have reset it. But I'm pretty sure it only samples about the last 1,000 miles or so. Reason I say this is I had gotten an oil change shortly before heading north 1,200 miles with my Camaro in my car trailer and I reset the one trip odometer to zero to track miles between oil changes. When I got up north my mpg was reading 9.5 after the 1200 miles. I looked at it about a month ago checking miles since the oil change. I had about 4300 and the mpg was 20.4. There is no way that I could pull my overall average above 20 mpg in 3000 additional miles if the computer was keeping a cumulative average since the last reset. I'd have to be getting 30+ mpg to get the average above 20.

 

[Rob5589]

After about a half dozen fill ups, the computer and manual calculations are within 1-1.5 mpg of one another. Close enough for me.

 

[ldoh]

I agree, the calculation only weighs the last so many miles. I recall another ram forum saying the last 100 miles but I couldn't confirm it in the owner's manual.

It wouldn't surprise me if the fuel mpg estimation was inaccurate as the gen 5 outside temp sensor is terribly inaccurate as temps rise into triple digits and there's really no reason for it other than a just ship-it production mentality.

 

[DraKhen99]

I agree, the calculation only weighs the last so many miles. I recall another ram forum saying the last 100 miles but I couldn't confirm it in the owner's manual.

It wouldn't surprise me if the fuel mpg estimation was inaccurate as the gen 5 outside temp sensor is terribly inaccurate as temps rise into triple digits and there's really no reason for it other than a just ship-it production mentality.

This is interesting, and lines up with what I'm experiencing. Sad, because I was going to use it to keep track of yearly fuel economy. I thought it was odd that it would rise and fall so much now with over 3,500 miles on my truck, whereas my last 2 trucks, both F-150s, after 1,000 miles or so, the MPG readout wouldn't change much unless I was on a road trip.

My lie-o-meter on the dash is now consistently .8-1.2 mpg off hand-calculated, which is better than my last truck's 1.4-1.8 mpg difference.

-John

 

[Dusty1948]

We all know that the exact way you fill up, how level the truck is, etc, etc can affect mileage calculations. But, with these distances and amounts of fuel, the discrepancies that could come from those variables is going to be in the tenths of a mile per gallon - not 2 whole MPG.

There is another variable. The fuel flow metering device that was used on early (1980s) Chrysler cars is not used on Rams. Instead, the computer relies on the fuel level sensor (gauge potentiometer) that signals the fuel gauge. If the linearity of that fuel level sensor is out of specification, there will be additional inaccuracy.

I've found that on my DT the computer is quite a bit more accurate than on my previous two DSs (4th gens). I am currently 0.5% within actual over the life of the vehicle, but I've had some fills that were as much as 9% off from actual. It appears your vehicle is quite new. I would suggest you do fill ups closer to an empty tank and then average over ten or more tank fulls. Checking fuel consumption on short mileage is generally not as accurate.

Best regards,
Dusty
2019 Ram 1500 Silver Billet Laramie, Quad Cab, 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, 18 inch wheels. Build date: 17 April 2018. Now at 019719 miles.

 

[ColoradoCub]

My Ram 2500 diesels have always been off by 1-2 mpg from what the hand calculated mileage is. I don’t understand how they can’t get something like that more accurate. But then again they claim these trucks get 22 mpg on the highway and while my truck does pretty good for a big V8 I am not getting 22 mpg on the highway!

 

[DraKhen99]

My Ram 2500 diesels have always been off by 1-2 mpg from what the hand calculated mileage is. I don’t understand how they can’t get something like that more accurate. But then again they claim these trucks get 22 mpg on the highway and while my truck does pretty good for a big V8 I am not getting 22 mpg on the highway!

That's because you have 3.92 gears. As it's been discussed before, RAM only certifies certain cab/bed/engine/drivetrain combinations, and if you look at window stickers, there's no difference in the rated fuel economy for 3.21 versus 3.92 trucks, whereas in the real world, it makes sense that there would absolutely be a difference.

The way I figure it, take the EPA rating and subtract 1 for the 3.92 RAR, and subtract another for being loaded with options (RAM apparently tests base-model trucks, thus affecting fuel economy when all the options are added - several hundred pounds' worth). That takes my 17/22 down to 15/20... which is more in line with what I'm seeing. It's been this way on the Big 3 trucks for many years.

-John

 

[ColoradoCub]

That's because you have 3.92 gears. As it's been discussed before, RAM only certifies certain cab/bed/engine/drivetrain combinations, and if you look at window stickers, there's no difference in the rated fuel economy for 3.21 versus 3.92 trucks, whereas in the real world, it makes sense that there would absolutely be a difference.

The way I figure it, take the EPA rating and subtract 1 for the 3.92 RAR, and subtract another for being loaded with options (RAM apparently tests base-model trucks, thus affecting fuel economy when all the options are added - several hundred pounds' worth). That takes my 17/22 down to 15/20... which is more in line with what I'm seeing. It's been this way on the Big 3 trucks for many years.

-John

And so although they create a custom Monroney Sticker with all the options on a truck is it not false advertising to put 17/19/22 as the fuel economy the vehicle is rated for with said options? The sticker should reflect the options IMO. It’s kind of like them putting 22 mpg highway rating on a Rebel that will likely get 4 mpg less than the sticker indicates. I’m not oncerned with the fuel mileage one bit as my truck regularly gets 18-19 mpg which I think is fantastic for a large V8, but there’s definitely some deception going on.