GM Equinox/Terrain Highway MPG Mystery, Part II

[Joe1]

I have been curious about the highway MPG numbers of certain GM vehicles. Many of their large vehicle highway MPG numbers rival the numbers of subcompact Japanese automobiles such as the Honda Fit and Mazda 2.

The thought of the EPA being a government agency and GM majority owned by the government...never mind, that would never happen in this country, would it?

 

[BBDartCA]

I had one of these new GM's as a rental this summer. Put over 1500 miles on it, about 90% on the freeway, and never got >20 MPG (by calculations). Very disappointed in the fuel economy.

It had a 6-speed trans. Noticed that it was very difficult to keep in 6th gear - frequently hunting between 5th and 6th.

 

[mechanicx]

Originally Posted By: Ursae_Majoris
Originally Posted By: JHZR2
Did they actually calculate it, or just rely upon a computer which Ive found can be off by 7%?


Did you read Critic's post? It plainly said that mileage was calculated at 29.265 MPG, whereas on board computer said it was 33.0 MPGs. That's a difference of 13%!!!!!


There is a discrepency but why should anyone concluded the on board computer is wrong and the "calculated" MPG is necessarily correct based upon what appears to be one fillup from a different station?

 

[LS2JSTS]

Originally Posted By: BBDartCA
I had one of these new GM's as a rental this summer. Put over 1500 miles on it, about 90% on the freeway, and never got >20 MPG (by calculations). Very disappointed in the fuel economy.

It had a 6-speed trans. Noticed that it was very difficult to keep in 6th gear - frequently hunting between 5th and 6th.


Sunday dinner provided some data to bring to the table.

My sisters Nox has just under 7,000 miles currently and is averaging 26.4 mpg in mixed used driving. Including daily short trips to and from work of about 5 miles.
My Fathers Terrain has a little over 10,000 miles and is averaging 27.8 mpg in similar mixed use driving.

FTR, they both keep logs at fill up and these are calculated figures, NOT DIC numbers.

For someone to average under 20 mpg with mostly highway use, something is wrong. Either with the car, your driving style or the calculation.

 

[IndyIan]

Originally Posted By: BBDartCA
I had one of these new GM's as a rental this summer. Put over 1500 miles on it, about 90% on the freeway, and never got >20 MPG (by calculations). Very disappointed in the fuel economy.

It had a 6-speed trans. Noticed that it was very difficult to keep in 6th gear - frequently hunting between 5th and 6th.

I guess washington is fairly hilly but still, that is pretty bad mileage. What do you normally drive and what kind of mileage do you get?
With a very tall 6th gear you have to accelerate fairly briskly to your desired speed and then let the trans go to sixth and then just maintain speed or gradually slow down. Gradually accelerating for miles then coasting for a bit, and then gradually accelerating again kills mileage big time.
10% throttle vs 14% hardly produces any acceleration but on my Neon its the difference between 40mpg cruising and 28mpg at 55mph.

 

[dwendt44]

Do rental units still have 'special' speedo and odometer gearing, so they read more miles than actual?

 

[moto94536]

It is impossible to get 32 mpg on gmc terrain. the car is heavy, compression ratio is high 11:4:1

to get close to that number, you have to drive 55 mph with cruise control.

 

[Nick R]

Originally Posted By: moto94536
It is impossible to get 32 mpg on gmc terrain. the car is heavy, compression ratio is high 11:4:1

to get close to that number, you have to drive 55 mph with cruise control.



Which is what the EPA tests it at. Or rather, at 50MPH if memory serves.

 

[Spyder7]

Originally Posted By: Nick R
Originally Posted By: moto94536
It is impossible to get 32 mpg on gmc terrain. the car is heavy, compression ratio is high 11:4:1

to get close to that number, you have to drive 55 mph with cruise control.



Which is what the EPA tests it at. Or rather, at 50MPH if memory serves.


Which just further discredits the EPA figure as almost nobody drives that speed on the highway. I get better fuel economy at 75 mph than 55 mph (due to gearing and the ignition timing setup), but I'm not pushing the same volume of air at either speed as the Equinox, due to a much smaller frontal surface area and lower drag coefficient.

-Spyder

 

[KrisZ]

I have one question, since I'm too lazy to look it up, is the EPA highway test done on a dyno or on a closed course?

 

[eljefino]

Originally Posted By: Nick R
Originally Posted By: moto94536
It is impossible to get 32 mpg on gmc terrain. the car is heavy, compression ratio is high 11:4:1

to get close to that number, you have to drive 55 mph with cruise control.



Which is what the EPA tests it at. Or rather, at 50MPH if memory serves.


The new for 2008 high speed test gets over 70. But it still looks like an on-and-off-the-gas disaster:

http://fueleconomy.gov/feg/fe_test_schedules.shtml

 

[mrsilv04]

Originally Posted By: dwendt44
Do rental units still have 'special' speedo and odometer gearing, so they read more miles than actual?


Why?

The vast majority of the rental car companies don't charge by the mile anymore.

Mostly, they rent with a mileage limit per day on "specialty" vehicles, such as 15 passenger vans, and sports cars (Mustang GT's, etc).

 

[KrisZ]

I just went to the EPA website, it looks like the test is done in a laboratory on a dyno. That would explain why a brick such an Equinox scored so well, no wind resistance and tall gearing.

The EPA website says that they adjust for wind resistance and weight, but how it is calculated. Perhaps it's just a percentage they adjust for, without any detailed calculations.

This whole thing is nothing but a sham, I see so many commercials claiming unbelievable gas mileages, like the Camry or Malibu, it’s just sad that people believe in these claims.

 

[kelpie]

Originally Posted By: moto94536
It is impossible to get 32 mpg on gmc terrain. the car is heavy, compression ratio is high 11:4:1

to get close to that number, you have to drive 55 mph with cruise control.


The compression ratio can explain less mpg if premium gas isn't being used. It would be interesting to do the calculations with 93 octane.

 

[rslifkin]

The EPA figures are definitely off by a bit for many vehicles. The average driver will usually be a bit below them (and then complain about it), while a reasonably efficient driver will beat them.

For example, my overpowered brick was rated at 13/17 on the old system, dropped to 11/16 with the new ratings. I typically get 12 - 13 city, 17 - 20 on the highway.

Also, I agree with the comments on cruise control. I can usually get better mileage than the cruise at 60 or so.