Author Topic: Diesel Mileage  (Read 20873 times)

Offline wildcatjason

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Diesel Mileage
« Reply #15 on: March 17, 2012, 12:12:24 am »
Here is a little math work to put that into one money saving scenario:

That 9 mpg avg. to 19.5 mpg avg. in my neck of the woods is just under 18 cent/mile decrease in fuel cost ($3.42 unleaded to $3.96 diesel).  I drove my truck a little under 10,000 miles last year so that would be almost $1,800 savings per year.  This assumes you don't drive it more now because you get better fuel mileage.

My 11 mpg avg. to your 19.5 mpg avg. at the same 10,000 miles per year is about 11 cents per mile so about $1,100 per year savings.

How much do you think you have in the conversion?  Are you running an overdrive transmission?  4X4 or 4X2?

Sorry for all of the questions, I am just not familiar with your truck or any conversion posts you may have.  Suppose I probably should have done a search before I started this response.
I don't get on here to often so sorry for the delayed response. The reason I decided to do the swap was because my whole drivetrain was wearing out, so i was going to put money into a diesel swap or to go through the  existing tbi 350. I have a ford zf5 behind it with a valair clutch. Its a very nice shifting close ratio tranny. That 19.5 is only city driving. I am mid 20s on the highway. It is a 2wd 3.42 geared burb. I have 6000 into it with a completely rebuilt drivetrain and a fiberglass tilt nose on the way. Hoping get near 30. If you're interested go to www.4btswaps.com. There is more then you'll ever want to know about that engine.

Offline wildcatjason

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Diesel Mileage
« Reply #16 on: March 17, 2012, 12:15:53 am »
Your fuel economy is not bad at all for all the city driving.  These are not exactly light weight vehicles so they take a lot of power to get up to speed.  I bet you can get over 30 mpg on the freeway with your combo and driving easy.  Best fuel economy is around 55-60 with these square nose trucks.  I drive almost all freeway so I can't comment on what kind of fuel economy my 6BT Cummins Suburban would get under the same circumstances as you.  However, I'm getting about 25 mpg on the freeway driving easy.  I also just swapped out the wide tires for some 265/70/17's so hopefully, I'll pick up a mile or two.

I think I remember you saying you advanced the timing.  That's helps some.
Since you do a lot of city driving, you might think about installing a lower stall converter.  Did you install a diesel converter?  Those are OK, but there are even lower stall converters out there.  The lower the stall, the less waste from slippage.  The Cummins has so much torque that slippage from a converter is not necessary for it to build power.
It's a 5 speed. I also found a fuel leak when my kdp fell out. In the process of replacing the timing case and installing a fiberglass front nose.

Offline Edahall

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Re: Diesel Mileage
« Reply #17 on: March 19, 2012, 05:50:14 pm »
Also, add a little bit of transmission oil or 2 cycle motor oil to your diesel.  I use 1 oz of the oil for every 2 gallons of diesel.  I heard that it helps to restore some of the fuel economy loss from the Ultra Low Sulfer reformulated diesel.

These trucks are also very sensitive to highway speeds.  With the high price of fuel, I keep my speed to no more than 60 mph for best fuel economy.  Back when diesel was cheap, I used to drive 75-80 mph with my 6.2L Suburban and it would only get 20-22 mpg.  However, since then, I have broken 30 mpg driving a steady 55 mph.
1990 ¾ ton 4x4 Chevy Suburban
-Cummins Diesel - 12 valve - factory rebuilt
-6 speed bullet proof manual transmission - NV5600
-Gear Vendors Overdrive
-Upgraded Holset HX-35 turbo
-NP205 iron transfer case
-3.73 gears
-2" Lift

Offline wildcatjason

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Diesel Mileage
« Reply #18 on: March 19, 2012, 06:06:25 pm »
Also, add a little bit of transmission oil or 2 cycle motor oil to your diesel.  I use 1 oz of the oil for every 2 gallons of diesel.  I heard that it helps to restore some of the fuel economy loss from the Ultra Low Sulfer reformulated diesel.

These trucks are also very sensitive to highway speeds.  With the high price of fuel, I keep my speed to no more than 60 mph for best fuel economy.  Back when diesel was cheap, I used to drive 75-80 mph with my 6.2L Suburban and it would only get 20-22 mpg.  However, since then, I have broken 30 mpg driving a steady 55 mph.
Im a still a lead foot. I also had schieders diesel treat. The quantity is more expensive, but since you can add 4 oz to a full 30 gallon tank it turns out being very inexpensive in comparison.

Offline tpull123

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Re: Diesel Mileage
« Reply #19 on: May 29, 2012, 07:31:21 am »
A couple of weekends ago I got a quite a few miles on my 6bt Cummins Conversion, seems to average around 21 mpg (mix of city and highway) which I was pretty happy with considering what it is.    Its a mildly built (370 hp / 875 ft-lb), 6" lift, 35" tires, dana 60, NV4500.   

Now only if diesel prices would come down a little bit...........that 21mpg would look soo much better vs a gas motor.
1978 Frame w/ Cummins Diesel, 85 cab and front end, and time well wasted....lots of it!

Offline tpull123

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Re: Diesel Mileage
« Reply #20 on: May 29, 2012, 07:36:13 am »
A picture of the truck....
1978 Frame w/ Cummins Diesel, 85 cab and front end, and time well wasted....lots of it!

Offline bake74

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Re: Diesel Mileage
« Reply #21 on: May 30, 2012, 08:35:38 pm »
     That is a sharp looking diesel, 21 MPG is not too bad at all.  One of these days I might just have to get me a diesel.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
  74 k10, 77k10    Tom