Diesel fuel economy mystery

2 years ago, I drove my 2000 Dodge RAM 2500 4x4 Cummins with a camper loaded
in the bed from San Jose to Long Beach. I drove a constant 70mph most of
the way and got a disappointing 13mpg both ways.

Last year, I did it again and again got 13mpg both ways.

This year, once again I made the drive with the same rig, but I got 15.5mpg
going and 14.5mpg coming back!
I also observed that while in years past I had to drive in 5th and floor it
to get over the grapevine at 65mph, but this time I just cruised right over
in 6th without ever hitting the floor.

In between last year and this, I flushed the brake fluid (it was dark and
dirty) and changed the manual transmission oil (it was not good, with water
in it). Both the brakes and transmission operation improved noticably after
this maintainence.

My question is: is there any chance that my brake and transmission
maintainence had anything to do with the jump in fuel economy?

--
S'later, Mike Locke

Mike Locke wrote:
>
> 2 years ago, I drove my 2000 Dodge RAM 2500 4x4 Cummins with a camper loaded
> in the bed from San Jose to Long Beach. I drove a constant 70mph most of
> the way and got a disappointing 13mpg both ways.
>
> Last year, I did it again and again got 13mpg both ways.
>
> This year, once again I made the drive with the same rig, but I got 15.5mpg
> going and 14.5mpg coming back!
> I also observed that while in years past I had to drive in 5th and floor it
> to get over the grapevine at 65mph, but this time I just cruised right over
> in 6th without ever hitting the floor.
>
> In between last year and this, I flushed the brake fluid (it was dark and
> dirty) and changed the manual transmission oil (it was not good, with water
> in it). Both the brakes and transmission operation improved noticably after
> this maintainence.
>
> My question is: is there any chance that my brake and transmission
> maintainence had anything to do with the jump in fuel economy?

Could also be normal engine break-in, fuel economy and power can increase the first 20-30K miles on a new engine. Unless the
brakes were dragging, fluid change should not affect MPG (but its a good idea to do regularly for long brake life) and the
tranny oil change may have helped, was the weight, grade and type/brand changed?

--
Roger

Hi,

Mike Locke <[email protected]> wrote:
#My question is: is there any chance that my brake and transmission
#maintainence had anything to do with the jump in fuel economy?

Brakes, no. Tranny, maybe a small amount that would only be noticable
on a cross-country trip like yours.

Are you sure you didn't replace the tires, or run them at a higher
pressure? Was the overall weight significantly different?

Another possible explanation is your engine was particularly tight when
new, and has finally broken-in.

Ken.
--
-------------------------------------------------------------------------
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WWW: http://www.charm.net/~kmarsh | heavy industries products.
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Regarding the transmission oil, there is only 1 oil rated for this
transmission (other oils including less expensive synthetics break down too
fast according to independent tests) so changing any of the parameters is
out of the question. The drained oil obviously had water in it (presumably
from condensation--it was brown and opaque) but was not exceptionally thick.

I was thinking that if engine break-in were a factor, I would have seen the
biggest jump in fuel economy between 2 years ago and last year. Am I
oversimplifying? The ODO is reading 23,000 miles right now.

A dragging brake was the first thing that came to mind, but it seems to me
that if a brake were dragging that hard I would have noticed a pull to one
side and also overheating brakes. Yes-no?

Same tires, now running at about 5PSI lower than in the past. I had the
right rear fender replaced (ouch! $$$$) as a result of a fender-bender late
last year.

--
S'later, Mike Locke

"Roger Brown" <[email protected]> wrote in message
news:[email protected]...
> Mike Locke wrote:
> >
> > 2 years ago, I drove my 2000 Dodge RAM 2500 4x4 Cummins with a camper
loaded
> > in the bed from San Jose to Long Beach. I drove a constant 70mph most
of
> > the way and got a disappointing 13mpg both ways.
> >
> > Last year, I did it again and again got 13mpg both ways.
> >
> > This year, once again I made the drive with the same rig, but I got
15.5mpg
> > going and 14.5mpg coming back!
> > I also observed that while in years past I had to drive in 5th and floor
it
> > to get over the grapevine at 65mph, but this time I just cruised right
over
> > in 6th without ever hitting the floor.
> >
> > In between last year and this, I flushed the brake fluid (it was dark
and
> > dirty) and changed the manual transmission oil (it was not good, with
water
> > in it). Both the brakes and transmission operation improved noticably
after
> > this maintainence.
> >
> > My question is: is there any chance that my brake and transmission
> > maintainence had anything to do with the jump in fuel economy?
>
> Could also be normal engine break-in, fuel economy and power can increase
the first 20-30K miles on a new engine. Unless the
> brakes were dragging, fluid change should not affect MPG (but its a good
idea to do regularly for long brake life) and the
> tranny oil change may have helped, was the weight, grade and type/brand
changed?
>
> --
> Roger

Mike Locke wrote:
>
> Regarding the transmission oil, there is only 1 oil rated for this
> transmission (other oils including less expensive synthetics break down too
> fast according to independent tests) so changing any of the parameters is
> out of the question. The drained oil obviously had water in it (presumably
> from condensation--it was brown and opaque) but was not exceptionally thick.

This was not stated originally, so was just asking if anything had been changed or not.

> I was thinking that if engine break-in were a factor, I would have seen the
> biggest jump in fuel economy between 2 years ago and last year. Am I
> oversimplifying? The ODO is reading 23,000 miles right now.

23K is pretty low miles, assuming it was 1/2 to 2/3 of that last year and near 0 the first year, that is fairly significant. I
would assume if it stays that way in the future, then breakin is a likely source of the improvement.

> A dragging brake was the first thing that came to mind, but it seems to me
> that if a brake were dragging that hard I would have noticed a pull to one
> side and also overheating brakes. Yes-no?

Usually, uneven brake pad wear, high wheel temps and a pull would be obvious signs. None of these symptoms were stated
originally, so I assumed they were not observed.

> Same tires, now running at about 5PSI lower than in the past. I had the
> right rear fender replaced (ouch! $$$$) as a result of a fender-bender late
> last year.

Could also be a fuel change, different brand or even summer vs. winter fuel.

--
Roger

"Mike Locke" <[email protected]> wrote in
news:[email protected]:

>
> 2 years ago, I drove my 2000 Dodge RAM 2500 4x4 Cummins with a camper
> loaded in the bed from San Jose to Long Beach. I drove a constant 70mph
> most of the way and got a disappointing 13mpg both ways.
>
> Last year, I did it again and again got 13mpg both ways.
>
> This year, once again I made the drive with the same rig, but I got
> 15.5mpg going and 14.5mpg coming back!
> I also observed that while in years past I had to drive in 5th and floor
> it to get over the grapevine at 65mph, but this time I just cruised
> right over in 6th without ever hitting the floor.
>
> In between last year and this, I flushed the brake fluid (it was dark
> and dirty) and changed the manual transmission oil (it was not good,
> with water in it). Both the brakes and transmission operation improved
> noticably after this maintainence.
>
> My question is: is there any chance that my brake and transmission
> maintainence had anything to do with the jump in fuel economy?
>

The diameter of your tires decreased by wear, hence more miles with the same
amount of fuel, hence better mileage....)

Head- vs tailwind might have done the rest....)

--
Bye,

Willem-Jan Markerink

The desire to understand
is sometimes far less intelligent than
the inability to understand

<[email protected]>
[note: 'a-one' & 'en-el'!]

Voodoo economics.

Willem-Jan Markerink wrote:
> "Mike Locke" <[email protected]> wrote in
> news:[email protected]:
>
>
>>2 years ago, I drove my 2000 Dodge RAM 2500 4x4 Cummins with a camper
>>loaded in the bed from San Jose to Long Beach. I drove a constant 70mph
>>most of the way and got a disappointing 13mpg both ways.
>>
>>Last year, I did it again and again got 13mpg both ways.
>>
>>This year, once again I made the drive with the same rig, but I got
>>15.5mpg going and 14.5mpg coming back!
>>I also observed that while in years past I had to drive in 5th and floor
>>it to get over the grapevine at 65mph, but this time I just cruised
>>right over in 6th without ever hitting the floor.
>>
>>In between last year and this, I flushed the brake fluid (it was dark
>>and dirty) and changed the manual transmission oil (it was not good,
>>with water in it). Both the brakes and transmission operation improved
>>noticably after this maintainence.
>>
>>My question is: is there any chance that my brake and transmission
>>maintainence had anything to do with the jump in fuel economy?
>>
>
>
> The diameter of your tires decreased by wear, hence more miles with the same
> amount of fuel, hence better mileage....)
>
> Head- vs tailwind might have done the rest....)
>

> Same tires, now running at about 5PSI lower than in the past.

Changing the tire presure changes the tire's rolling radius (distance
from the axle center to the ground). That affects the speedometer/odometer.
That change in odometer could be where you're seeing hte difference in
milage.

Mike