Everything is newly tuned up, all filters changed, timed at 5 degrees BTDC.. Even a new catalytic converter and freer flowing muffler.. 5 speed and stock size tires. Its a long bed. Not raised. Stock 20R motor does have power steering and AC ( mileage is without the AC on) Why only 16 mpg city and 18 highway?? I turn 3K at about 65 mph....

 

you turn 3k at 65mph!

try upping your tire height a bit i bet that will help

 

3K at 65 mph is not bad for a 4 cylinder... Up my tire height and the odometer will turn that much slower. Yeah the revs will go down but who knows what the accurate mileage will be?

 

yep, that engine is designed to turn that, it's also got 4.38 gears instead of 4.10s like '82 and newer trucks since the transmission had higher gears than the later models. however if you have a 5 speed it's had a tranny swap done sometime in its lifetime, as the only tranny available in a 4x4 that year was a 4 speed.

16-18 is pretty typical for a 20R, if you baby it you might push 20 in a 4x4.

 

Would a header do anything for me? It a long tube type..

 

The problem is you have to turn that rpm to have the power you need. The 20R doesn't have a lot of power - only had like 90hp, and that was optomistic. 5 speed could help, but not by much, you still can't drop your rpms much or you lose enough power you still aren't gonna better mileage, but it will be doggy too.

That engine responded pretty well to upgrades if I remember right. Anything that gives you a bit more power is likely to help in the cruise mpg department too.

If you are running 225s (stock size) try 235s or 30x9.50s next time. The small increase in diameter might make the difference without ruining drivability, and will look better too.

 

actually the 20R isn't going to have much less power than a 22R...its high revving characteristics make up for its (slightly) less torque than a 22R.

there weren't 225s back in '79-80, at least for this truck. they came with H78 mud/snow rated tires

 

It's not hard to figure odometer error. For that matter probably 90% of the Yotatechers have a wrong odometer...
Go from stock 225s (27.5" diam) to:
235s (28.5") =4% low reading =@65 actual mph the speedo reads 67.6 mph
30s (29.5) =7% =@65 actual mph reads 69.5 mph
31s (30.5") = 10% =@65 m actual mph reads 71.5 mph

So when you figure your fuel mileage, just add the proper percentage of miles to the odometer total before doing the math.

But one good question is- Do you know if your odometer is accurate NOW? Have you checked it?

 

Actually, i have 30x9.50's on there now and the speedometer/odometer is very accurate... Did a long mileage check and it was right on par with my new car.

 

that aint to bad thats what i get with my 90 22re 5 spd... well i don't get 18 very much mostly about 16

 

This gives me an idea. I think I'm gonna put some gas in the GF's car each night. She drives approx 120 miles a day, so it won't take long before she starts really worrrying...

 

X-cab turbo 2wd with camper . Stock 25 mpg cityand 33+ highway. 60mph highway 2200rpms.

 

I went back and added that in to my log, made quite a difference in my averages and totals.

 

also i think there's the variable of winter gas. i'm pretty sure that's what we've got right now, since my '91 dropped to about 19-20mpg instead of the 23-24 i was getting when i bought it in august.