Fuel economy in new cars

[gizzsdad]

Originally Posted By: itguy08
Probably closer than most will admit to. The computer knows exactly how much fuel goes into the tank. Do you know how much gas you put in to make the tank "Full" and where that is each tank? Over time the 2 will get very very close to each other.


My experience as well.

 

[TiredTrucker]

I am not convinced the OEM's are even trying all that hard to do better on fuel efficiency. My 1998 Chevy 2500 with a 454 (7.4L) big block averaged similar mpg as my current 2015 2500 6.0L. Now that is sad. 17 years and no improvement.

 

[Gasbuggy]

Originally Posted By: itguy08
Originally Posted By: Gasbuggy
You should run a few tanks on paper and see how accurate that gauge is.


Probably closer than most will admit to. The computer knows exactly how much fuel goes into the tank. Do you know how much gas you put in to make the tank "Full" and where that is each tank? Over time the 2 will get very very close to each other.


I know how much gas goes into the tank, the station pump certified by Weights and Measures tells you. Filling up at the same pump eliminates any "but where is full" concerns. The cars computer makes less accurate assumption based off where the level sensor is, but the computer does not use that information when determining mpg on the display so I'm not sure why you think that matters.

It is well known that the computer readouts are not to be assumed as accurate until verified by the correct manual method of checking gas mileage. Though I have met people too incompetent to check it correctly themselves. I've personally seen them 3 mpg higher than what is correct, and it was on a Dodge. Now, why would they do that, let me think...

 

[Quattro Pete]

Originally Posted By: Gasbuggy
I know how much gas goes into the tank, the station pump certified by Weights and Measures tells you. Filling up at the same pump eliminates any "but where is full" concerns.

I doubt it. Even if you use the same pump, there is no guarantee it will always shut off at the exact same spot every time. The sloshing gas can make it turn off sooner or later. Besides, even the same pump can get out of whack over time and dispense more slowly than before, again affecting the shut off point.

 

[grampi]

Originally Posted By: TiredTrucker
I am not convinced the OEM's are even trying all that hard to do better on fuel efficiency. My 1998 Chevy 2500 with a 454 (7.4L) big block averaged similar mpg as my current 2015 2500 6.0L. Now that is sad. 17 years and no improvement.


I agree. Automakers seem to be more interested in seeing how many electronic bells and whistles they can cram into a vehicle than they do improving fuel economy...if they put as much effort into improving MPGs as they do putting these giant, distracting, jumbotron screens into their vehicles, full sized pickups would be getting 40 MPG by now...

 

[itguy08]

Originally Posted By: Quattro Pete
Originally Posted By: Gasbuggy
I know how much gas goes into the tank, the station pump certified by Weights and Measures tells you. Filling up at the same pump eliminates any "but where is full" concerns.

I doubt it. Even if you use the same pump, there is no guarantee it will always shut off at the exact same spot every time. The sloshing gas can make it turn off sooner or later. Besides, even the same pump can get out of whack over time and dispense more slowly than before, again affecting the shut off point.


This X100. You can't see the tank and therefore have no idea where full is. Where the pump clicks off is only the spot where it senses fuel splash. That can be different pump to pump, tank to tank, etc. Do you stop at the first click, go 2 more, try to top it off? Did you hold it open at max flow, use stop 1, 2, or 3? Was it hot or cold (affects volume), etc? All can have an effect on hand calculated MPG.

Think of it this way - you have to fill up a glass full. But you cannot see inside it - it's black and all you have to fill it is a small straw. You have no idea exactly where Full is. You just have to guess. And over 2, 5, 10, 20 fill ups you will never get exactly the same in there. But over those you will get close to an accurate fill level.

And yes the computer knows exactly how much gas goes into the engine. Based on injector pulse width and feedback via the O2 sensors.

Most MPG meters are a rolling average anyway (mine is last 500 miles) and they tend to go down quickly but come up slowly. When I hook the camper up to the truck it drops like a rock and stays there. Takes "forever" to bounce back.

I've got over 100k of data showing that for my vehicles the MPG meter and hand calculations are very, very close.

 

[HTSS_TR]

I think the fuel economy of newer vehicles are much better than 10-20 years ago mainly because better transmission, wind resistance, tire ...

If you take 2 same size engines of 1995 and 2015 and run them at same speed of 3000 RPM, both engines will consume similar amount of gas, the newer engine may consume a few percentage less but as much as EPA rated.

Now if you look at engine speed of 1995 car at 70 MPH you may see it running at 3000 RPM, same engine size in similar sized vehicle of 2015 may see 2000 RPM or lower at the same 70 MPH.

I am pretty sure that an engine would use much less gas running at 2k RPM instead of 3k RPM for the same road speed

 

[GiveMeAVowel]

That's because cars today, even smaller vehicles, are bloated
pigs filled with nanny safety gear, and all manner of
excessive electronics. I'm not saying you shouldn't be able to buy one of these bloated pigs if you want, but where are the choices for those who don't want this? We have perhaps two models that sort of match that requirement in the US, if that.

I want the choice to be able to delete things like stupid
and potentially deadly airbags, ect.

 

[hattaresguy]

Yep, I averaged 17.5 MPG the other day with my pickup doing about 90.

I'd like to see a 1990 half ton do that, heck going 90 would be an adventure!


I went from a 14-15 mpg truck with 190hp and 2wd, to a 16-17 MPG truck with 305hp and 4wd.

 

[oldmaninsc]

Originally Posted By: itguy08
Originally Posted By: Quattro Pete
Originally Posted By: Gasbuggy
I know how much gas goes into the tank, the station pump certified by Weights and Measures tells you. Filling up at the same pump eliminates any "but where is full" concerns.

I doubt it. Even if you use the same pump, there is no guarantee it will always shut off at the exact same spot every time. The sloshing gas can make it turn off sooner or later. Besides, even the same pump can get out of whack over time and dispense more slowly than before, again affecting the shut off point.


This X100. You can't see the tank and therefore have no idea where full is. Where the pump clicks off is only the spot where it senses fuel splash. That can be different pump to pump, tank to tank, etc. Do you stop at the first click, go 2 more, try to top it off? Did you hold it open at max flow, use stop 1, 2, or 3? Was it hot or cold (affects volume), etc? All can have an effect on hand calculated MPG.

Think of it this way - you have to fill up a glass full. But you cannot see inside it - it's black and all you have to fill it is a small straw. You have no idea exactly where Full is. You just have to guess. And over 2, 5, 10, 20 fill ups you will never get exactly the same in there. But over those you will get close to an accurate fill level.

And yes the computer knows exactly how much gas goes into the engine. Based on injector pulse width and feedback via the O2 sensors.

Most MPG meters are a rolling average anyway (mine is last 500 miles) and they tend to go down quickly but come up slowly. When I hook the camper up to the truck it drops like a rock and stays there. Takes "forever" to bounce back.

I've got over 100k of data showing that for my vehicles the MPG meter and hand calculations are very, very close.


I agree. I have found the GM computers to be fairly close to what the "hand" figures were. I have driven the Impalas on many long trips (some 400 miles each way other 1,500 miles each way). I love getting 30 - 33 MPG on the freeway from a full size car with a decent amount of horsepower (300).

 

[supton]

Originally Posted By: itguy08
Originally Posted By: Quattro Pete
Originally Posted By: Gasbuggy
I know how much gas goes into the tank, the station pump certified by Weights and Measures tells you. Filling up at the same pump eliminates any "but where is full" concerns.

I doubt it. Even if you use the same pump, there is no guarantee it will always shut off at the exact same spot every time. The sloshing gas can make it turn off sooner or later. Besides, even the same pump can get out of whack over time and dispense more slowly than before, again affecting the shut off point.


This X100. You can't see the tank and therefore have no idea where full is.


Loved my VW, filled it to the brim (literally) on just about every fillup it had. I figured that ought to be very repeatable.

 

[Andrew1972]

Fuel economy is great however you pay dearly in asking prices currently.

 

[itguy08]

Originally Posted By: supton

Loved my VW, filled it to the brim (literally) on just about every fillup it had. I figured that ought to be very repeatable.

Got to love Diesel.

 

[leeaspell]

The wife's 2.5 fusion gets 35mpg hiway, hand calculated. Her previous car, a 2012 elantra got 43mpg, hand calculated on a 6000k trip across Canada.

My 04 hemi gets like 10mpg on the hiway, and close to zero in town lol. My 2012 F350 gets about 20mpg highway, with dog/egr/ scr delete.

 

[Gasbuggy]

Originally Posted By: oldmaninsc

I agree. I have found the GM computers to be fairly close to what the "hand" figures were. I have driven the Impalas on many long trips (some 400 miles each way other 1,500 miles each way). I love getting 30 - 33 MPG on the freeway from a full size car with a decent amount of horsepower (300).


My Cadillac computer average is consistently within 1 tenth of the average I calculate by hand. How can this be with all these inaccurate gas pumps and fuel that somehow sloshes differently each time I fill up making accurate readings impossible? (sarcasm) It's consistent because the events during fill up are consistent because I make an effort. While you may not expect 100% accuracy it will be better than what the average car computer is producing. Over a length of time, if keeping track tank to tank, the old method eliminates the variables and gives you a very accurate reading.

Some light reading.

http://www.edmunds.com/fuel-economy/your-fuel-economy-gauge-is-fibbing.html

http://blog.caranddriver.com/why-your-tr...-how-to-fix-it/

 

[Hokiefyd]

Originally Posted By: dishdude
I was driving last night thinking about a couple threads where people mentioned how good fuel economy was in some 80's and 90's econoboxes. I don't disagree, but as I was playing around with the instrument cluster in my Jeep, it hit me that this large SUV with a V6 that puts out 290 hp gets the same mileage as one of my first cars did - a beat up old K-car with a 2.2 that brand new put out a tire scorching 93 hp. By time I got it with a gazillion miles on it I am sure it was a lot less! Considering the weight, size and performance of this vehicle, is there ever a better time to be a car guy? This large vehicle gets 24 MPG without me even trying.


I agree with you that newer vehicles and powertrains are generally very efficient, locale and climate can have as great of an effect on economy than many other factors. For example, I think you used to live in Pittsburgh, right, and now live in Phoenix? Those are probably close to the two extremes of potential economy -- Phoenix is probably one of the better places to live to achieve good economy, and Pittsburgh is perhaps one of the worst. Phoenix offers a generally hot climate and wide and flat roads -- all generally favorable for efficiency. Pittsburgh has a much colder climate and lots and lots and lots and lots and lots...of hills -- lousy for even attempting to get good efficiency.

I saw that first-hand when I moved to the flat NC coastal plain from the Blue Ridge Mountains of southern Virginia. My vehicle at the time, a '97 Cadillac SLS, would struggle to get 15 or 17 in town. "Town" was a hilly Blacksburg, VA, with 25 mph speed limits and stop signs everywhere. But down here, I saw an immediate improvement -- to around 20 mpg in town and 30 mpg on the road. Streets are wide and fast around here (45 mph speed limits). The climate is warmer. The terrain is flatter. All boons to efficiency.

Even all that said, you'll still get no argument from me that modern vehicles aren't more efficient. Look at a 2015 Jeep Grand Cherokee AWD 3.6 and compare it to a 2005 Jeep Grand Cherokee AWD 3.7, and to a 1995 Jeep Grand Cherokee AWD 4.0.

The 2015 is 17/19/24, the 2005 is 15/17/19, and the 1995 is 14/15/18. And the 2015'll run circles around either of the other two.

If I recall correctly, your Grand Cherokee is 2WD, right? That's the best case scenario: 17/20/25 ratings. You at 24 speaks to the relative ease of Phoenix driving. Keep it up -- I bet you could easily best the highway rating on your normal commute.

 

[itguy08]

Originally Posted By: Gasbuggy

My Cadillac computer average is consistently within 1 tenth of the average I calculate by hand. How can this be with all these inaccurate gas pumps and fuel that somehow sloshes differently each time I fill up making accurate readings impossible? (sarcasm) It's consistent because the events during fill up are consistent because I make an effort. While you may not expect 100% accuracy it will be better than what the average car computer is producing. Over a length of time, if keeping track tank to tank, the old method eliminates the variables and gives you a very accurate reading.


That's what I've been saying. Over time the 2 will converge. Trying to establish a trend over 1 or 2 tankfuls introduces lots of opportunity for error. Especially since one could be a rolling average.

My 2 vehicles over well over 100k (96k on 1 and 30k on the other) have gauges and the hand calculations via the RoadTrip iOS app are VERY close, almost statistically the same. And I make 0 effort for consistency.

 

[oldmaninsc]

Originally Posted By: Gasbuggy
Originally Posted By: oldmaninsc

I agree. I have found the GM computers to be fairly close to what the "hand" figures were. I have driven the Impalas on many long trips (some 400 miles each way other 1,500 miles each way). I love getting 30 - 33 MPG on the freeway from a full size car with a decent amount of horsepower (300).


My Cadillac computer average is consistently within 1 tenth of the average I calculate by hand. How can this be with all these inaccurate gas pumps and fuel that somehow sloshes differently each time I fill up making accurate readings impossible? (sarcasm) It's consistent because the events during fill up are consistent because I make an effort. While you may not expect 100% accuracy it will be better than what the average car computer is producing. Over a length of time, if keeping track tank to tank, the old method eliminates the variables and gives you a very accurate reading.

Some light reading.

http://www.edmunds.com/fuel-economy/your-fuel-economy-gauge-is-fibbing.html

http://blog.caranddriver.com/why-your-tr...-how-to-fix-it/


Well there you are - anything on the internet MUST be true!

Neither article did much to impress me. Too many generalizations. Doing the hand calculations has in my opinion a much wider margin for error. Pull up to a different pump and the angle the car is sitting at can be different. After the pump shuts off, do you add more? 1/4 of a gallon, 1/2 a gallon or more? Does the pump pump at the same rate every time? For example one station close to me has a noisy pump, and when someone on the other side of the pump from me starts pumping gas, the pump slows way down.

Just because one writer thinks a Honda trip computer is optimistic doesn't mean all of them are, but by the same token maybe not all are as accurate as GM's are!

I'm agreeing with ITGUY - over the coarse of a long trip (in my experience) the two different methods often come out very close.

 

[hattaresguy]

Hand calculations are worthless unless you do a lot of them. One or two tanks is useless data, for every tank over 50k+ miles gives you a pretty good average. The more tanks you calculate the more you average out the filling errors and the driving errors that you will get.

I don't bother with them anymore, I find the vehicles computer to be good enough.

Most people only calculate a couple of tanks, that's where you will see big MPG swings. Or they will get a super high number because over one tank conditions were just about optimal than run with it. What really matters is lifetime MPG average since that's what costs, IE over 100k ownership miles. Not one tank on a trip, again interesting but largely pointless data.

 

[grampi]

Originally Posted By: GiveMeAVowel
That's because cars today, even smaller vehicles, are bloated
pigs filled with nanny safety gear, and all manner of
excessive electronics. I'm not saying you shouldn't be able to buy one of these bloated pigs if you want, but where are the choices for those who don't want this? We have perhaps two models that sort of match that requirement in the US, if that.

I want the choice to be able to delete things like stupid
and potentially deadly airbags, ect.


It's because automakers want to produce as few different versions of a given model as possible, and the one that makes them the most profit is the bloated one...