8 MPG?

I love being listed as a junior member @ 73 years old !!!!

One thing I noticed not mentioned. Have you corrected the speedo for the 36' tires? If not , you are putting more miles on than indicated, hence lower MPG.

MisterB said:

Are you talking about a gauge like this? This is the best I could get it adjusted a few weeks ago when I did it

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Pretty close, I was talking more like these...



While driving keeping it close to 20 in. Hg. will help. Basically you're driving like a grandma.

My K5 I had a built 350 (10:1, mild cam, 2.02 corvette heads, performer intake with 750 Holley DP re-jetted), 4sp, 4.11 gears, 205, and 35s. No emissions bs either. If I wasn't playing I would get 16-18 mpg depending on city/hwy. If I was playing you would see the fuel gauge drop (40 gal. tank). Probably 4-6 mpg. Estimated about 300 HP.

MikeB said:

Assuming your engine is stock, 15" is low. Should be closer to 20". Heck, even with a moderate performance cam, my 355 will make 18-19" at idle.

Have you checked for small vacuum leaks -- at both ends of vacuum hoses, EGR valve (if equipped), carb gasket, distributor canister, etc?

As for gas mileage, I haven't measured it on my 82 C10, but my old 69 C10 with a mild 350 would get 13-14 on a highway trip. It had a 3.08 axle and 29" tires, also 600 cfm Eddy 1406 carb, cast iron manifolds, and dual exhaust. I had that carb tuned so it was right on the ragged edge of being too lean.

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I'm not sure what cam it has. The EGR valve is brand new, as is every single hose, hose fitting, and clamp. I'll have to run it again, but closer to the engine, because the one I chose to use was the longest and easiest hose to get to, which was the brake booster hose.

Also, I'm at 2,000 feet above sea level, and the manual says higher altitudes might effect the gauge to say you're not in the normal range, when really you are.

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78 Jimmy 2WD said:

One thing I noticed not mentioned. Have you corrected the speedo for the 36' tires? If not , you are putting more miles on than indicated, hence lower MPG.

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That's a good point. Somehow the speedometer is on. I have verified it with GPS, and also those radar speed signs that show your speed when you drive by a school zone or whatever.

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MisterB said:

Also, I'm at 2,000 feet above sea level, and the manual says higher altitudes might effect the gauge to say you're not in the normal range, when really you are.

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I’m at 1600ft but 1/2 hour west is ~500ft and 1/2 hour east is 3-4000ft. Atmospheric pressure ranges from ~100kPa at lower elevations and mid 90kPa at 3-4000’, but my idle kPa only varies 1 point or so.

nujac said:

The title on the truck says 3/4 ton but it is not a full floating axle.

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From what I’ve seen, 3/4 ton trucks don’t come with full floats, but rather a sf.

First time I took '81 on a trip, I used google maps and added each and every beginning point, stop, turnout, location we went to, everything. 8 mpg's after it was all said and done. Was disappointed because the truck ran so well. That was cruising no faster than 65 with cruise control set, unless it was backroads, or mountain roads.

Heck, my old '65, Mean Green got 14-16 with a stock engine and 3.54 gears cruising 70 (2,600 rpms). My current '65, Crusty Biscuit gets 12-14 with a basically stock engine with unknown miles and 3.19 final drive (2,600 rpms). But it'll cruise in direct drive, which is 4.57 gearing, and get 12, you're just not going faster than 55 (3,000-ish rpms).

DoubleDingo said:

First time I took '81 on a trip, I used google maps and added each and every beginning point, stop, turnout, location we went to, everything. 8 mpg's after it was all said and done. Was disappointed because the truck ran so well. That was cruising no faster than 65 with cruise control set, unless it was backroads, or mountain roads.

Heck, my old '65, Mean Green got 14-16 with a stock engine and 3.54 gears cruising 70 (2,600 rpms). My current '65, Crusty Biscuit gets 12-14 with a basically stock engine with unknown miles and 3.19 final drive (2,600 rpms). But it'll cruise in direct drive, which is 4.57 gearing, and get 12, you're just not going faster than 55 (3,000-ish rpms).

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I guess it's the price we pay for having a big square box rolling down the road lol.

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MisterB said:

I guess it's the price we pay for having a big square box rolling down the road lol.

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It is. What gets me is my older trucks get better mileage than the square does.

That’s about right

I’ve bought several trucks that were stock and lifted them
My experience has been

Figure 13-14 mpg bone stock with no lift and 225 28” tires

And you will lose 1/2 MPG for every inch of additional tire diameter

and 1/2 MPG for every inch of lift

So if you do a 6” lift you’re gonna lose 3 MPG and if you go from 28” tires to 35” tires , you’re gonna lose another 3 MPG

The engine makes a difference too
When we did the LS swap and had it tuned , with a 4” suspension and one inch hockey puck body lift and 35” tires with 3.73 axles
It went from 8.5 with the old worn out TBI 350 to 15 with a tuned LS

We also had a 02 4wd Jeep Liberty bone stock with tiny tires and it gets 14

shiftpro said:

A warmed up 350 with 4 barrel in a 2wd can get 20 mpg... I've done it.

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Tell me how! I've changed over to EFI and still only get 7mpg if I'm lucky. I have a feeling I've got to tear it down and rebuild it.

Raybo135 said:

Tell me how! I've changed over to EFI and still only get 7mpg if I'm lucky. I have a feeling I've got to tear it down and rebuild it.

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Down a steep hill! [emoji23]

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Raybo135 said:

Tell me how! I've changed over to EFI and still only get 7mpg if I'm lucky. I have a feeling I've got to tear it down and rebuild it.

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Post #25 in this thread.

Well you can always remember that the gas is cheaper than the depreciation on a new truck that doesn’t get much better mileage

It amuses me how some people agonize over the MPG of a new vehicle and never factor in the depreciation. Which will almost always be considerably more than the fuel costs

My latest personal vehicle is a 06 4wd expedition limited , with every option , heated and cooled seats etc ,
that I got last year , from an elderly guy trading it in on a new Buick .
I paid him $3,500, which was what Carmax offered him and $500 more than the Buick dealer offered

He bought it new and paid $47k
And put 90k miles on it
At 14 mpg he used 6,500 gallons , and at $3 a gallon he spent about $20k on fuel , and lost $43k on depreciation

I buy large comfortable gas guzzling vehicles for wholesale when they bottom out price wise, and I don’t worry at all about the MPG

The vehicle before that was a 04 4wd expedition , with 100k on it
Original owner paid $44k , sold it to us for $6,500.
We put another 110k on it and sold it for $3,000

The one before that was a 4 runner with 100k I’m the clock and we paid $9k , we put another 220k on it and sold it with 339k on it , for $2,000
, only reason it didn’t bring $4k was the suspension , shocks , springs and bushings and steering rack was totally worn out and it really wasn’t safe to drive at 77 mph , which is what I usually set the cruise on

My employer has me driving a ‘17 3/4 ton 4wd chevy and it gets 12.5
Unless I’m towing , then it gets 8

I’m sure if you put a six inch lift and 35s on the 2017 it wouldn’t get much better than the lifted square

You need to start a small business for the tax deduction
Friend of mine is a construction inspector for a lender , drives all over the place , he gets a new 4 wd crew cab pickup every 3 or 4 years and the tax deduction pays for the truck in lowering what he has to pay Uncle Sam every April