| MPG vs driveablilty [message #149636] |
Mon, 14 November 2011 10:50  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
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Senior Member |
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We are all trying to get better MPG both in the GMC and our personal vehicles.
I recently bought a new 2011 GMC pickup with a 5.3L engine. It has some technology to run on 4 cylinders, variable valve timing (I'm told) and a 6 speed transmission. Its suppose to get 9.5 l/100km on the hyway and 14.4 l/100km in the city. It carries my tool kit (15lbs) has a tonnel cover.
My old truck got passed down as a new shop truck. Its a 2005 Chev with a 5.7l engine. It has a cab-high cap on the back and carries about 1000 lbs of equipment and tools.
We needed to go to a site about 4hrs round trip away. For fun we both fueled up and reset the Ave Mpg display.
The result new truck 12.2 l/100kms Avg and the old truck was 12.4. we refueled when we returned and both took about the same fuel.
The new truck does about 1400rpm at 100kms/hr. On flat level hyways it goes to 4 cylinder mode and the instantaneous MPG drops to about 9.5ish l/100kms. However it doesn't take much to drop back to 8 cylinder mode. I think the engine computer runs under windoze as it takes it a while to decide to shift back, like a long hesitation. If cruise is on, then you have lost some speed and suddenly its shift down & 3600 rpm to gain back 6-7kms. Not fun. Watching the instantaneous MPG, what you gain in the 4 cylinder mode is lost shifting out and gaining back speed.
With the old truck the engine is right there, step on it, no hesitation it just goes. You can tell its loaded with some weight though. It never gets MPG below likely 11 l/100kms, it just lumbers along at a constant speed not needing to shift down, unless its a steep grade.
When I get my new truck loaded up the same, I think I'll be using Tow/Haul mode alot.
So GMC has thrown a few million $ at developing all this technology and added it to the price of the vehicle. In real life when this truck gets loaded up, I think I'll lose MPG compared to the old.
Sorry for the metric.
Just my experience.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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