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On 6/19/2004 6:57 AM, Ned Buckmaster wrote:
| I have a 2000 club cab 2X4, and my friend has a 2003 quad cab 4X4,
both with
| 4.7L engines and automatics. He swears (and I believe him) that premium
| gasoline gives him at least 2 more mpg than regular. When I try premium in
| my 2000, I see no difference at all in gas mileage. We have both tried
this
| over multiple tanks. His gets ~13 on regular, 15 on premium. I get 15.7 on
| everything.
Has he shown you actual data? Is he actually calculating the mileage,
or is he going by the overhead MPG display (which is very
well-documented as being inaccurate). What type of driving is this? If
he's running regular around town, and premium on the highway, it's clear
where the real difference is.
My '03 QC 4x4 w/ the 4.7 and manual transmission is running 15.85 MPG
since I bought it (calculated mileage - I fill up every time, so I know
how many gallons I've burned and how many miles I've driven on those
gallons). That's 22,000 miles all on 87 octane.
I ran 89 in my '99 5.2L for a while, then went back to 87 because I
didn't want to keep paying extra money (this was when prices started
jumping) for *worse* mileage than I got on 87.
Both the 4.7L and 5.2L are designed to run on 87. Higher-octane fuel
has less energy per unit than regular - you get the power gains by being
able to run higher compression (higher octane is less prone to
detonation). So the same amount of premium will net you less energy to
the wheels, as compared to regular.
| It seems to me that His has a knock sensor or something adjusting his
| timing, and providing better mileage (and power) with premium gas.
I don't think Dodge uses knock sensors, at least on the truck engines.
The idea was tossed around for a while here a few years ago, but I think
I did hear that they aren't on our trucks.
| Is there a difference in the engine electronics
| between these two years?
Almost certainly there is a difference in the programming, both in the
engine and in the transmission computers. You have a 5-speed
transmission (extra overdrive, I think), whereas he only has a 4-speed.
~ Same part, different program which allowed them to cook up an extra ratio.
| Can I update mine somehow?
Likely not, as the dealer is only allowed to apply a program that's
approved for your specific setup (that's what I was told at a dealer -
they also aren't allowed to remove a "new" program and revert to the
old, if that's been done, as was the case on my '99). And there'd be no
guarantee that you'd get better mileage. You're doing well for a
4500-pound, V8, automatic transmission 4x4 - keep running regular and
enjoy it! If anything, your friend should be asking for ways to improve
his mileage.
- --
- -andy
http://home.rochester.rr.com/alevy/dakota - andy-dml@levyclan.us
- --------------------------------------------
"Whatever Adam does, do the opposite and you'll be fine"
-Bob Tom
- --------------------------------------------
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