Suburban Gas Mileage?

[Old Dave]

I have a 86 suburban 1/2T 2WD that used to get 15-16 MPG on the highway at 65 MPH. I bought it when it had 91K on it. The 700R4 let go shortly after I bought it and I had it rebuilt. The transmisssion has about 90K since it was rebuilt. The engine was completely rebuilt recently along with the factory quadrajet. The best mileage I have gotten so far on the road is 11.1. Engine has about 12K since the rebuild so it should be broke in. Just wondering what everyone else is getting? I know this thing can do better than what's it's doing now.

[gchemist]

One guy posted 18 MPG with a 400 SB/700R4/3.08 rear end.

I would check to see if your torque converter is locking up. Do you have tach available?

Start with a good tune up. Check your time setting. Check your brakes for any dragging, stuck drum or caliper, front tire rotationo on the spindal, collapsed cat, air intake problems.

[Hooter]

i would recomend you check: tires condition and pressure, brakes dragging, bad wheel bearings, timing a bit off, engine running too rich, tranny torque coneverter lock up or maybe now you are kicking in the 4 barrels too much?

[Old Dave]

Engine was just rebuilt again for the second time by the same guy. He rebuilt it a year ago and it still used a qt. of oil every 1000 miles and puffed blue smoke everytime you started it. He put valve seals and new intake guides in twice (first time he didn't pull the heads but the second time he pulled the heads and did it the right way according to him). He assured me after the second time he put seals in it this would take care of the problem but it didn't. So while we were on a trip to Colorado the first of August he pulled the motor and went through it again. He said he found a torn valve seal on the #7 cylinder. Supposedly he honed it out and installed new rings, rod and main bearings and put it back together. The crank was new (not ground) a year ago. I've only put about 350 miles on it since getting it back but it doesn't seem to smoke when you start it. Time will tell on the mileage when I get more miles on it. BTW it has no cat converter(went by the wayside after the first overhaul), brakes are new all the way around, timing is correct (I checked it myself after the second overhaul), torque converter locks up about 40-45 mph and into 4th gear at about 50-55. Don't have a tach on this but could rob (borrow) the one off my son's 70 chevy and just see what it's running at highway speeds. The one thing I've noticed is when you take off it shift into 2nd gear at about 5mph and into 3rd at about 20. It's done this ever since the 700R4 was rebuilt about 90K ago. This is the first O.D. I've owned and I don't know if this is correct or not. Anymore thoughts?

[gchemist]

If your tranny is shifting at 5 MPH your killing it!! Adjust your TV cable to bring the shifting points higher. The torque converter lockup sounds about right. Mine are a little lower but I have less weight and a 1800 stall. My tranny guru recomends the following shift points

1-2 15 MPH
2-3 25-32 MPH
3-4 43+ MPH really depends on throttle acceleration.

The TV cable should be fully pulled at WOT. The best valves for heads are the umbrella type. They seal better than all other types of seals.

What is your rearend ratio?

[jimss420]

I have a '79 c10 2wd with a 350 thats mildly modified, with a turbo 350 trans, 3.08 gears and the speedo is exactally right, it gets 15 mpg on the hwy going 70 mph at 2600 rpm, (14 mpg with the a/c on and going up grades)

[jimss420]

oh yeah another thing, the only smog equipment that is on it is a High flow cat and an pcv valve, all that other crap sits in in the back of the garage for the 2 years i dont have to smog it (i live in CA).