Matt81

I seem to remember reading somewhere on this forum that the average highway mileage for a c3 is ~20mpg. Even on the best of days, my 81 with TH350 gets less than 15. Am I misinformed, or is there something wrong with my car? Torque converter not locking up? At least gas prices aren't $1.80+ around here anymore!

Neo Fender

20 MPG highway average for a C3 is very unlikely except for maybe an '82. I average 13 MPG city in my '79.

Monkeywrench

11MPG (downhill)... don't complain... :lol:

Paul L

I average 10-11mpg in the city and ~14 on the highway.

Gator81

My '81 gets 16-17 around town and 22-24 on freeway trips (when I behave myself :) ). I have checked the mileage of consecutive tanks of fuel running 70 mph with the A/C on and gotten an average of 24 mpg. This is with the stock 2.72 rear gears, 4-speed, and a Summit 330-hp crate engine. Mileage is a little better than it was with the stock L-81 engine, due mostly, I believe, to efficiencies gained from the higher compression (a little over 9:1), the more advanced timing curve, and the mid-range torque orientation of the Crane 2040 cam. But even with the stock engine, the car still got over 20 mpg on the freeway. And that's at higher altitudes (Utah, Idaho, Wyoming). Your '81 oughta do better than what you're seeing. I'd bet the carb needs a rebuild and your timing is probably not advanced as much as it should be.

Tom73

Both of my 73's (L82 auto and LS4 4-speed) get about 13 MPG on the highway. I would love to get 20 but..... :(

tom...

UKPaul

I agree with Gator81 (Hi, Gator :seeya ). My '81 WAS getting just over 20mpg (imperial gallon) if driven sensibly. Dropped dramatically if I got a bit "enthusiastic" & wore my Lead boots ;) . After my locking torque converter keeled over the mileage has dropped to below 20. May be worth checking if yours is locking up OK. Does the engine need a tune up? Are you running under inflated tyres (that has a bigger effect on mileage than you'd expect)?
Paul

Matt81

Any tips on how I can check to see if my torque converter has gone the way of the dodo?

mayberg

I get 7 mpg and a whopping 7 highway!

Maybe I'd get better mileage if I didn't burn the back tires every chance I get, huh?

KorbenDallas

WOW! I don't feel bad anymore knowing stock is about 13mpg!!! Sweet! :cheers:

(8mpg here) :cool:

GORDO77

My stock 77 with L48 350 trans and 3.08 gears got 15. with new 700r4 i get 21 highway. :seeya

UKPaul

Drive at a constant speed above 55mph(?) & gently push the brake pedal down. This will unlock the torque converter so, if it is locking OK, the rpms should increase by about 300.
Good luck,
Paul

Neo Fender

Also, you'll have to wait for the engine to warm up. The converter lock up function is temperature controlled and will not activate until the coolant has reached a pre-determined temperature.

KenSny

I get about 15-16mpg with combined in-town and highway driving. Everybody "remembers" getting good gas mileage with the older cars, but it just wasn't the case in the mid-'70s. If you got 20mpg then you were not driving a 350 or larger V8.

andyg

I have checked a few times and estimated 14MPG.That is as long as I stay out of the secondaries. Then its more like GPM... :D


----Andy