Wierd MPG...

[big61fourby]

Went on my first road trip with this truck over Christmas, 350 miles one way, primarily interstate, speed limit 70 with some 75; revs in the 2400 rpm range. Thought I

[Dvldog 8793]

Howdy
Things to consider-
The type and grade of fuel used
exact amount of fuel in tank
and the most important part is that the 6.5 has it's best MPG at around 1700-1800rpm. I've never noticed that much difference above 2000rpm but drop down into the high teens and then it really shines.
L8r
Conley

[gvig]

When I bought my truck three years ago, I also bought a fifth wheel, 31 aol at about 9K loaded. I pulled it from Oklahoma to northern WA and back. Some killer hills too. Got from 12 to 14 mpg but no real power and bad overheating problem. Found a bad IP and bad injectors. Changed them, corrected the timing. Have since added the exhaust system, gauges (no help for mpg), cooling mods, and remote mount of the FSD. Just pulled from Ok to southern CA. All the improvements netted me an improvement all the way down to an even 10 MPG, and it doesn't seem to matter if I am busting my gut to pull big hills or running flat in Texas.

I share your frustration :mad:

I can't really recommend what I did as it seemed to move me in the wrong direction. Good luck anyway, hope you find some improvement.

[gvig]

One other thing, when running empty, I have noticed that the more I enjoy the sound of my new straight exhaust :D the lower the mpg goes. Driving with the windows rolled up seems to help the mpg, for a not so obvious reason :D :D

As has been pointed out, the right foot and rpms are the factors you have the most direct control over.

[big61fourby]

I always fill up at the same station here in town, small truck stop place with quick-fill pumps. I believe the station is Connico (sp?)? Used a similar station on the trip, think it was Texaco. I waited as long as possible to let the foam subside and get as much fuel in as possible, but could this be a substantial factor?

Also, to confuse the issue even more, I've been using my truck for work, driving 150 miles to job sites and back, while running for 5 hours. Lots of idling, and still gets close to 14 mpg. Any other ideas?

On edit: I guess my speedo and tach aren't exactly accurate, as I'm running slightly larger tires, 265's, I believe.

[slagona]

You'll notice a much bigger gain in MPG if your speed is under 60 MPH.

I had never seen mileage above 15 MPG until I purchased my '99 6.5 TD 1500 4WD Suburban with the 3:42 differential. Previously all my diesels were 6.2's or 6.5TD's with 4:10 diffs.

I drove the suburban home from the Philly area to the Detroit area. I filled the tank before leaving Philly. Filled up again during the trip. Then filled up again just before I reached home. Now, there could be some error due to different gas stations and such, but I calculated 21.2 MPG on that trip. Going 55 MPH 90% of the time and always under 60 MPH.

My normal driving style in the 60K + miles I've put on the suburban since that trip has resulted in average MPG of 16-17 in the summer and 15-16 in the winter. However, I normally drive at 75 MPH or better.....

So, what will it be? Better MPG or a quicker trip? I still chose the quicker commute....

However my commute is now being done in a 2006 VW Jetta TDI - first tank netted 38 MPG at 75 MPH or better - often much better than 75 MPH....

[moondoggie]

Good Day!

Please don

[big61fourby]

moondoggie,

Good point about the few number of tankfulls. I've only owned the truck since last July, and this was the first real roadtrip with it, so time and more trips, situations may produce different results.

I need to update my sig., but I ditched the K&N right before the trip. It was in pretty bad shape, the PO never cleaned it, and it was full of dirt, grim, etc. I gave it a good cleaning and ran it for a while, but it still looked bad and wouldn't hold the oil, so I went with a regular filter with the intentions of reworking the intake/filter setup in the not so distant future. Couldn't tell any SOTP difference after the swap.

I guess I was just surprised that I didn't see more of a difference between the two trips. Hopefully I'll get a chance to get the rpms down in the 1700 range and see what that does.