Mpg to expect on an '82 C20 3+3, 350?

[Thesiger]

Am I crazy for hopping to get at least 14 MPG highway with a beast like this? I hear 12 a lot, but I assume that's with the 454. Thoughts?

 

[HotWheelsBurban]

Everything I ever heard on these was single digits. But with overdrive automatics, that should help.
For comparison, my '97 (GMT 400/OBS)C3500 CCLB with 4L80E and 5.7 Vortec gets 10 ish around Houston, and 13-14 on the highway with just the family in it. Last road trip was with a full bed and heavily loaded trailer. That was 11-11.5.....

 

[85K304SPD]

High hopes. Expect 5-10 maximum. If you keep the RPMs down, unloaded.

 

[Frankenchevy]

I wouldn’t expect 14 to happen with a truck that I assume has a th400 trans. 12 might even be optimistic. 10-11 average sounds about right. If your empty, have nice H/T tires pumped up well, engine is in a good state of tune and were very careful with throttle and braking inputs, you might knock down 12…

Where are you driving mostly and what rear gear does it have?

 

[HotWheelsBurban]

I know on the Burbs '90 was the last year that didn't have overdrive automatics. My R2500 Burb with a TBI 350, TH400 and 4.10s would usually get around 10 or 11 in town, a little bit better on the road. Cruising speed was around 55 or 60 with no OD....
The newer truck with 5.7, overdrive and 4.10s will cruise at 65-70 all day while engine RPM is around 2000-2200. So OD makes a huge difference.

 

[Thesiger]

I'd mainly do 55 on country roads, to and from work, easy driving. its an automatic, let me figure out the rear gear and if she has overdrive...

 

[SquareRoot]

I get a verified 14-15 on the highway at 70mph. 85 K20. But, it has only cost me untold thousands of dollars which will NEVER be recouped in fuel savings.

350 Vortec, Electric fans, Pro-Flo4 EFI, NV4500. These 3 ton bricks will never be efficient but the fun factor is off the hook!

 

[Thesiger]

Can't get the ratio and trans right now... It's a friends vehicle. Out of interest and for comparison sake, what'd a 1/2 ton 4x4 350 auto '89 suburban get? 16 highway on a good day?

 

[gmbellew]

Can't get the ratio and trans right now... It's a friends vehicle. Out of interest and for comparison sake, what'd a 1/2 ton 4x4 350 auto '89 suburban get? 16 highway on a good day?

I have a 1990 4x4 suburban. it has a 350tbi with a mild cam and a tune. the rest of the drivetrain is 700r4 and 3.73 gears sitting on a 3in lift and 33x10.5xr15 BFG AT. cruising at 74-75, I get ~13mpg. maybe with stock tires and cruising at 70 you may be 14-15mpg. stock tires and flat land cruising at 55-60mph and I'd expect you'd hit 16-17mpg. I think that's what they were EPA rated when new when the speed limit was 55mph

 

[k1500]

Smiles per gallon vs mpg.

 

[Rusty Nail]

Single digits.
If you are counting on much better you might oughta keep shopping. Sure it's possible but perhaps at a great expense or and maybe those trucks are owned by mechanic types that know what they are doing under the hood.
Tell ya what, if it's gonna make you upset - don't calculate it. I drove less than 450 miles last month and bought two $100 tanks full in 4 weeks.

Then again I daily drive a 35 year old 4x4 that doesn't leak a drop. It ain't cheap but I do it because I want to and because I can. Ain't for everybody.

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[Thesiger]

I already daily drive my 86 305 and it's not terrible on gas. though making as little as I do in my situation at my age I really shouldn't! I like them trucks too much.

 

[Strick]

79 C20 Crew, 350 & SM465 with 3.73 gears. 12 MPG average.

HS

 

[peats]

I would expect 10mpg.

 

[HotWheelsBurban]

I know on the Burbs '90 was the last year that didn't have overdrive automatics. My R2500 Burb with a TBI 350, TH400 and 4.10s would usually get around 10 or 11 in town, a little bit better on the road. Cruising speed was around 55 or 60 with no OD....
The newer truck with 5.7, overdrive and 4.10s will cruise at 65-70 all day while engine RPM is around 2000-2200. So OD makes a huge difference.

Update: I ran a tank of mid grade 89 octane gas through the CCLB, and the in town mileage jumped from 10.5 to 13.85! That's worth 40¢ a gallon. No freeway driving, just surface streets. This next tank will be interesting, because we have some freeway driving on our trip to the model car club show this past Saturday.
So this illustrates how something you don't think about, like gas selection, can make a big difference! Several of us on the 400 forum have been discussing mileage and performance, and it was suggested that trucks might run better on the middle grade. It did in my case; truck ran well on 87 but is better and smoother on 89.