Help- '06.5 mpg at 13

[Jeff22]

I bought this thing one year ago with 100k on it and it and it was getting 15mpg. Now at 140k the mpg is at 13, it has been slowly getting worse. This is a big dissapointment considering that my old 85 chev with 150k on the 6.5T gets 20mpg consistantly. Whats wrong with this thing? It runs fine and has tons of power and no mods that i know of besides cat delete.

[More Power]

How's it perform otherwise? Starting? Smoking? Rattle? Power?

While sitting in the dentist's chair the other day, my dentist (a Duramax owner) told me he recently rebuilt the transmission and installed a new billet torque converter. He also said his fuel economy jumped by good bit. Apparently, a no code transmission with issues has more effect on fuel economy than I might have guessed.

Jim

[Mark Rinker]

Check for proper boost level
Check for clogged or restricted exhaust
Check for clogged or restricted intake
Check for dragging brake(s)
Tire inflation

[Jeff22]

Engine starts easy, runs very smooth and seems to have all the power it should have. It will smoke a little at idle but it doesn't seem to do it all the time. It does make a strange sound out the exhaust sometimes while idling though I can't describe it right now cause I haven't heard it in a long time. Only other time it smokes is if its been a long time, say a week or two, since i have stepped on the gas hard and then romp on it for the first time. Air filter indicator is working properly but shows no restriction because i replaced the filter in January after plugging it with very powdery snow. Have you ever heard of a muffler plugging? I cut out the cat for the sole reason of eliminating that as a restriction point. I will jack it up and check for dragging brakes. Guess for that matter I could just see if any brakes are hot after my next drive. I run tire pressure where they squat just a little, about 75 front and 55 rear. On the trans. deal I hope I never know if thats the cause of poor economy, it would take a lot of fuel to make up that expense. Never thought I would be so impressed with an automatic.

[Mark Rinker]

What oil do you run, and what (if any) consumption between changes?

Couldn't keep Rotella in my 6.5s. Vaporized at least a quart between 5K oil changes. When I switched to Mobil Delvac, the mileage started to improve.

Whether this was from better compression, less fouling of turbo/oil vapor return system, cleaner injector tips, or all of the above - I'll never know for sure, but the increase was measureable and lasting.

[Jeff22]

I use John Deere +50 15w40. Same oil as just about every other engine in my operation. Its always still on the full mark at around 10K when I change it. And I too noticed that on my 6.5 the oil seems to dissapear. A lot of smokey looking vapor coming out the vent but hardly enough air to feel on your hand.

[Mark Rinker]

How many miles on the injectors? If original, the answer is probably in the droplets of fuel a few of them are a-dripping, rather than the fine spray they should be a-sprayin' ;)

[Jeff22]

As far as I know the injectors are original. Shouldn't they run a lot longer than 140,000 miles?