Nobody warned me about the MPGs on these square bodies!

[WranglerTJForum]

Today marks the second time my square body has run out of gas on me.

In fairness, it's my own fault. When I bought the truck the dual fuel tanks didn't work (only the main tank worked) and the fuel gauge was in no way whatsoever accurate. My next project is fixing the tanks (as anyone knows who has been following my threads on this forum). Still, I figured I've got 16 gallons in the main tank and that should be enough to get me to and from since I don't do much driving.

Oh boy was I wrong! Today my square body ran out of gas on me for the second time and left me stranded on the side of the road. I was shaking my head thinking I just filled the main tank a few weeks ago and I'll be damned if I've driven more than 50 miles (if that), unless I am forgetting something.

I had the thing towed home, put more gas in it, and it fired right up.

I know, stupid me. The fuel gauge doesn't work so how could I ever really know for sure? Still, my main driver which is a 2019 F150 3.5 Ecoboost gets much better (though not great) MPG. I figured that the K10 would get much worse MPG than the F150, but I had no idea it would be this much worse!

I suppose it doesn't help that I've got a 500HP Blueprint Engines 396 stroker in there with a Holley Sniper EFI setup. No idea what sort of MPG it's getting but after today I'm convinced I'm getting 8 MPG at best.

Anyways, I didn't buy this thing for the MPG (obviously) but I had no idea this thing would suck gas the way it does! Talk about a wakeup call

The cold weather and snow is about to set in here in rural Wyoming so it's time to get started on the fuel tank project!

 

[DoubleDingo]

8 is what they get. Fill it up before leaving town and don't get stranded. Take a jerry can too.

 

[WranglerTJForum]

8 is what they get. Fill it up before leaving town and don't get stranded. Take a jerry can too.

I learned that lesson the hard way, twice! From now on I'll be carrying my NATO gas cans with me in the back. I've owned a lot of vehicles that suck gas; this one tops them all by quite a margin!

It'll be nice to have the aux tank (and fuel gauge) working.

 

[DoubleDingo]

I learned that lesson the hard way, twice! From now on I'll be carrying my NATO gas cans with me in the back. I've owned a lot of vehicles that suck gas; this one tops them all by quite a margin!

It'll be nice to have the aux tank (and fuel gauge) working.

If the exhaust sounds really good, the right foot usually gets WAY heavier!

 

[nvrenuf]

What are these “mpg’s” you speak of?

Something else you should know about fuel gauge operation - 1/4 to E does not move proportionately with F to 3/4, that last 1/4 to E is way faster!

 

[WranglerTJForum]

If the exhaust sounds really good, the right foot usually gets WAY heavier!

Yep, and this one sounds really darn good!

What are these “mpg’s” you speak of?

Something else you should know about fuel gauge operation - 1/4 to E does not move proportionately with F to 3/4, that last 1/4 to E is way faster!

I know how that goes! In my case the fuel gauge works but it's off the charts entirely. I've got a Dakota Digital VHX cluster that I'm going to install which should hopefully be more accurate.

 

[legopnuematic]

Even with your setup you should be able to hit double digits, unless if you really are in the skinny pedal all the time.

 

[83Stepper]

I get a lot of smiles per gallon, if that counts lol. But yeah I've got a spreadsheet that I track my mpg, all maintenance and repairs as well. With a cammed 350 and a 3 spd Saginaw, I've getting an average of about 10mpg. Some weeks are closer to 9 and others are closer to 11.5. And yes, the better that it sounds, the harder it is to get decent mpgs lol.

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[fast 99]

Both of my K20's with a stock tire diameter are highly tuned, checked with infrared and in good condition. One with 411 gears gets around 10 other one with 373 11-12 thats it.

Suppose a gear vendor overdrive would help [a little] but they aren't driven much more than 2k a year. Economics don't work out. Gas is way cheaper than any new truck payment.

 

[WranglerTJForum]

Mines got a 700R4 with 4.10 gears and 33X10.5 tires.

I agree, gas is way cheaper than a new truck payment. In addition, I can actually work on this thing myself and it's enjoyable. Can't say the same for any modern vehicle.

 

[Hilllbilly]

I get 12 mpg, 350/th400/4:10 gears/35 tires/ '81 k20

My 2005 dodge ram 4x4 3500 sht bed, cummins diesel, 3:73 gears gets a easy 25 mpg , 65 mph, on the highway .... Yeah buddy !

 

[Terlingueno]

85 K20 Sub

I get 14-ish mpg depending on tailwind or not.

350 Goodwrench 10067353 crate, Eddy 1405+2101 performer intake, headers, SM465, 4.10 gears in the pumpkins, LT 235 85R 16's.

Original engine/Quadrajet got 14-ish depending on tailwind. Didn't drive over 55-60 much at all then. Still don't...

 

[gmbellew]

Mines got a 700R4 with 4.10 gears and 33X10.5 tires.

I agree, gas is way cheaper than a new truck payment. In addition, I can actually work on this thing myself and it's enjoyable. Can't say the same for any modern vehicle.

you should be doing better than 8mpg with an OD transmission (assuming you have some highway time mixed in). my 1990 burb with 33s, 700r4, 350tbi will pull down 13ish on the highway at ~75mph unless i am fighting wind. around town it does 10.5ish.

 

[WranglerTJForum]

you should be doing better than 8mpg with an OD transmission (assuming you have some highway time mixed in). my 1990 burb with 33s, 700r4, 350tbi will pull down 13ish on the highway at ~75mph unless i am fighting wind. around town it does 10.5ish.

The state highway that goes from town to our house has a posted speed of 70 MPH. I'm regularly doing 75-80 MPH.

Being as though this is Wyoming I'm almost always fighting wind (sometimes lots of it). Since mine is a '73 and doesn't have baffled tanks, I'm wondering how much fuel is actually left in there when it sputters and dies.

Of course when it died I was going up a hill. When I got it back home to flat ground I noticed it started even without filling the tank.

 

[nvrenuf]

My 2005 dodge ram 4x4 3500 sht bed, cummins diesel, 3:73 gears gets an easy 25 mpg , 65 mph, on the highway ....

No offense but I’d have to see that hand calculated in person. I’ve got an 06 2500 4wd Megacab w/ 6spd & 3.73’s, I’ve never gotten better than 16.5 (hand calculated since new). My overhead instant average always displays approx 6~7 mpg’s high.