Realistic suggestions

[Camarrow]

Since trading my truck for a avalanche for my wife I have been looking for a truck to drive to work/play farm with. Before buying a truck my wife and I have been trying to pay off bills because of a possible summer layoff at the plant I work at. Yesterday she got the check book statement and decided to find where all are money is going. Well for last month we payed $357 for gas to drive to work (does include a trip to vale Co). Though the trip is in there it still should be about what we pay every month since we didn't use the other car while gone and didn't drive much while there. So here is the question. I have been looking at a 86 K20 with a 80K 6.2 and a banks. The truck has a 400 and 4.11s. I average about 60-65mph and rarly go over that speed, so need for a freeway screamer. I am I fooling myself into thinking that a low geared 3/4 ton will get 15-18 mpg? The seller says he gets 16-17 but that is hard to trust. I drive 60+ miles to work a day so pulling isn't that big a deal, it is more I like the heavier axles (lots of friends with 8.5 10 bolt falures as of late). I could swap in 3.42s but would cost $1200 (free labor + lockers). Should I just find a late model 1/2 ton 6.5 and deal with the Computer/injection pump problems. I guess I just really need to be sure that I won't be buying a 12mpg truck. Anyone else have any 80s 3/4ton experences?

[NH2112]

I'd say you could hit 15-18 if you didn't take off or accelerate quickly, ran 33" radial A/P or A/T tires at a high pressure, and set the pump so you JUST get black smoke when you load the engine down. A set of Goodyear or Bridgestone heavy duty tires (load range F) would help, too, since the stiff sidewalls and tread would keep rolling resistance to a minimum.

[rjwest]

I had a 82 heavy 3/4 ton Std 4 speed od with 3.73 rear 24 MPH highway Honest that was average
over 150 k miles..... 15- 17 with 25oolb
truck camper.....

I suspect the auto will use more fuel.

[86burb]

My '86 K20 Suburban TH400 4.10 lockers averages 17-18mpg with 33" tires @ 80 psi.

[G. Gearloose]

My old '83 K20 (8600 gvw) NA, 4.10 , 700R4 got over 20 mpg (corrected)highway with 35" mud terrains.

My old 84 K20, NA 8600gvw, M465, 4.10 and 245R75's got 22 mpg highway.

My '84 K5, Banks with 4.10, (10.5" fulll floater) 700R4 gets 21 mpg (corrected) with the same 35" mud terrains.

I suspect 18 for a suburban is realistic, if your gentle. Perhaps minus 1 more for the TH400.

If you get 12 mpg, somethings broke, or release the parking brake.

[arveetek]

My '86 K-10 with 3.73 gears, 465 manual tranny, and 31" tires averaged 14-16 mpg.

My '81 conversion with 4.10 gears, 27" tires, and 700R4 overdrive averages 18-19 mpg.

My '86 C-10 Suburban with 3.73 gears, 700R4 overdrive, and 235/75/R15 tires averaged 19 mpg.

My '77 K5 conversion with 3.08 gears, 235/75/R15 tires and TH350 tranny averaged 22 mpg.

The higher (lower number) axle ration and overdrive tranny makes all the difference. The lower (higher number) ratio gives more power.

The truck you are describing, I would not expect to see over 16 mpg unless the fuel injection pump is set for maximum economy.

Casey

[84 Convert]

My crew cab has gotten between 13 and16MPG in mixed driving mostly between 60 and 70+MPH always 8500lbs+ sometimes up to 19000lbs GCVW. I think your seller is probably selling you straight. Oh, yeah, I also have a big lumber rack and 8' wide flatbed to help with wind drag. I run 235/85R16's rated for 65psi at about 55-60psi. Be sure you buy GOOD FUEL! It does make a difference.

Gregg

[Camarrow]

Just so I know. When you guys say injection pump "tuned for economy" what exactly do you mean? Is this to turn the screw out? How far out can it be turned? I know a diesel doesn't get lean but does the EGT get high or something? I know basicly what that screw does but just for fun someone explain it to me so I don't look dumb later for thinking I know.

[britannic]

The fuel pump adjustment affects the stroke of the plungers that create the inj. line pressure and fire (pop off) the injectors. You can achieve a similar result to lowering the injected fuel rate by keeping your foot out of it at higher loads and speeds. Injection and cam timing is a critical factor in fuel economy, as is engine breathing (free flowing intake and exhaust).


Originally posted by Camarrow:
Just so I know. When you guys say injection pump "tuned for economy" what exactly do you mean? Is this to turn the screw out? How far out can it be turned? I know a diesel doesn't get lean but does the EGT get high or something? I know basicly what that screw does but just for fun someone explain it to me so I don't look dumb later for thinking I know.