"Real World" diesel fuel mileage on Duramax

[Reg]

Too bad they discontinued the INST ECON on the DIC.
What that helps one to really comes to terms with is that it is the amount of fuel consumed on starts (lot of fuel, very little distance) that REALLY determines "mileage".
It takes a LOT of downhill "freewheeling" to make up for one stop light.
Contesting merging lanes drinks down fuel too, for what ? 50 ft ?

I have been working on my "driver calm" for quite a while now (-:
but is does seem that I still do a "slightly" harsher take off from a light that I didn't quite make the green on - that sucks down fuel too.

MPG is the reciprocal of rate of fuel consumption.
Basic arithmetic - you a get VERY distorted view of things when you deal with reciprocals, ESPECIALLY if you try to somehow "average" them, whether by actual calculation or intuition.
Not to "get all metric about it", but the European practice of expressing it as fuel per distance is more realistic, e.g. liters per 100 Km.

Yes, the DIC sometimes does apparently lie.
My solution was to measure actuals (including the ODO against 100 miles of highway markers to the nearest 1/10) and figure the correction factor.
I monitored it for a long time, the correction factor has remained constant.

As far as wheel size is concerned - we just had this conversation on 24 inch vs 28 inch tractor rims (R4s vs R1s). You need the tire width and profile to figure it all out - actually the rolling circumference.
Since all internal ratios are indirect these days what you probably want for overall gearing is MPH/K_revs e.g. at 2,000 RPM highways speed is somewhere in the range of 60 to 70 ?

BTW, my D'max seems to get thirsty at much over 2,000 RPM
(subjective)

 

[Diamondpilot]

I had the same issue with my 2003 Ram. Not the diff but 3 trannys in 68,000 miles, cooling fan, power steering pump, AC compressor, ect. Traded at 68,000 but the dealer was good about it, just a POS truck.

Now I had the a different experience with a 1989 Chevy. Blown motor and transfer case all before 35,000 miles. 2 lawyers later I dumped it and got a Toyota Truck that I traded at about 170,000 miles with less than $100 in repairs for all them miles....

A good dealer makes all the difference when dealing with a problem vehicle.

You are smarter than me though. I would give Dodge another chance since my local dealer took good care of me. I bought 3 more GM's and both cars were ok, not great but not bad. My 05 3500 4x4 Dmax was also a POS going to the dealer 15 times in the first 9 months. Traded for a 06 F350 diesel 4x4 Ford at a major loss and its been nearly perfect needing only a new Fuel Gauge.

Chris

 

[jeffster]

Yep, external tranny filter must be changed at 500 miles to keep the warranty valid on the Allison.

Chris

Chris, can you point to a reference for this? It is not in my 2006 owner's manuals or my 2012 owner's manual. I just looked at both of them, as well as the Allison site for the 1000 series transmissions. It seems finding accurate info isn't always easy, so I could be missing it and just not know. Thanks!

 

[Diamondpilot]

Chris, can you point to a reference for this? It is not in my 2006 owner's manuals or my 2012 owner's manual. I just looked at both of them, as well as the Allison site for the 1000 series transmissions. It seems finding accurate info isn't always easy, so I could be missing it and just not know. Thanks!

I was show by my dealer when I bought my 05 and I am pretty sure it was in the maintenance schedule in the owners manual. My neighbors 07 need it at 500 miles also.

Try a google search?

Chris

 

[jeffster]

Chris, I did search and couldn't find any reference. Looks like Allison is generically showing 50k for first filter change:

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=SA5429EN.pdf

However, Allison does show a GM supplement in their FAQ that shows GM recommends the first one be done at 7500 miles:

". Beginning with MY03, GM Truck is recommending that the spin-on filter (filter only; not transmission fluid) initially be changed at 7,500 miles. Following that, the filter and fluid should be changed at the recommended intervals."

That was found here:

Allison Transmission

Personally I always change them with each oil change. They are cheap insurance and take only seconds to change.

-Jeff

 

[Bigkrank]

Seems like fuel mileage varies on the ones around here. My 2007.5 LMM was averaging 19-20 unloaded until an updated ecm reflash then it averages a very consistant 17.5-18 unloaded. The "liar" DIC is always within a tenth or two so I gave up hand calculating.

One friend bought one at the same time and his has struggled to get over 11 mpg since day one. Another bought one after ours and his gets 18 average.

Two other guys in the area have 2011 3500 duallies w/ the DEF and seem very happy. One went from a Dodge duallie and the other had a 2007 GMC duallie.

I am planning on dropping the DPF after the warranty runs out this fall.

The dash does have some issues though on the older ones:
one million miles - Diesel Place : Chevrolet and GMC Diesel Truck Forums

 

[Diamondpilot]

I have heard 500 miles and 5000 miles but never more. I personally would call your service dept.

Chris

 

[dodge man]

On your D-Max, I thought if you had DEF, your truck didn't go through a regen cycle. I thought the DEF elimnated the DPF. I'm just guessing though.

 

[Bigkrank]

On your D-Max, I thought if you had DEF, your truck didn't go through a regen cycle. I thought the DEF elimnated the DPF. I'm just guessing though.

No, still regens, just not as often, DPF still hanging under there on GM trucks anyhow.

 

[MF1552]

The Allison transmission spin-on filter should be changed at the first service, whether you change oil by mileage, time interval, or wait until the Change Engine Oil message comes on the DIC.