LIVEAnimals
1/2 ton status
90 V2500 Sub
TBI 350/400
4" lift 315s
stock 4.10s
and I get a wonderful 9 mpg
TBI 350/400
4" lift 315s
stock 4.10s
and I get a wonderful 9 mpg
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
MPG Thread, curiosity
- Thread starter sled_dog
- Start date
89 Fullsize Jimmy
350 TBI/700r4/ 4.10 Gears
35" tires, 6 inch lift
All the goodies from CFM Tech for the TBI
~ 13 MPG
350 TBI/700r4/ 4.10 Gears
35" tires, 6 inch lift
All the goodies from CFM Tech for the TBI
~ 13 MPG
redsuburban90
Registered Member
1990 Suburban
383/edelbrock carb
8 inch lift/ 38's
th400
9mpg....
383/edelbrock carb
8 inch lift/ 38's
th400
9mpg....
ccarley
1/2 ton status
1989 1/2 ton Suburban V1500 (4X4)
TBI 350, Jegs TBI spacer and Salad Bowl
TH700R4, 3.73's, True Trac rear with BFG 35" A/T's
10 to 12 mpg, all the time. Speedo is not corrected though, and its 10 mph off at 65 mph. So it may be better than 10 to 12 (since I'm traveling farther than what the odometer is reading).
Now that I've done all the work with the heads, I'm willing to bet it will be better. Also added the TBI pod spacer. I keep track at every fill up, so we'll see how this goes.
TBI 350, Jegs TBI spacer and Salad Bowl
TH700R4, 3.73's, True Trac rear with BFG 35" A/T's
10 to 12 mpg, all the time. Speedo is not corrected though, and its 10 mph off at 65 mph. So it may be better than 10 to 12 (since I'm traveling farther than what the odometer is reading).
Now that I've done all the work with the heads, I'm willing to bet it will be better. Also added the TBI pod spacer. I keep track at every fill up, so we'll see how this goes.
hillbilly deluxe
Professional Pile-It
Here's my junk:
93 K3500 DRW Extended cab Flatbed
6.5 T.D. NV4500 Weighs ~7200 lbs.
4.11's, stock height/wheels.
17 mpg highway. I never paid too much attention to town mpg.
96 1500 Suburban
6.5 T.D. 4L80E 6500 lbs.
3.42's, stock height/wheels.
15 city, 18 highway
73 K2500 Suburban
Stock old ass 350 w/Q-jet. Headers and exhaust. SM465. Weighs 6400 lbs.
4.11's. ~6" lift with 37's.
D60 front, 14 bolt rear.
About 10 mpg combined. The speedo broke a long time ago so that figure is old.
As for the 6 mpg.
A few years ago the '73 'Burb was running like crap and getting about 4 mpg. I decided to do a tune up. I took off the distributor cap and it looked like the internals came off the Titanic. So I replaced the distributor with a new one ($115) and replaced the carb with a rebuilt Jegs Q-jet ($300). Mileage went from 4 to 10. The throttle was also amazingly responsive compared to before. Before I did any mods I once got 14 mpg on a highway trip.
For me the key is not to exceed 2500 rpm on the highway. With the 4.11s and 37s that's about 65 mph so it's cool. I have to hit 3100 rpm to go 75 and it absolutely swills fuel at that speed so it's not worth it. Can't do much about the town mileage except creep around...
93 K3500 DRW Extended cab Flatbed
6.5 T.D. NV4500 Weighs ~7200 lbs.
4.11's, stock height/wheels.
17 mpg highway. I never paid too much attention to town mpg.
96 1500 Suburban
6.5 T.D. 4L80E 6500 lbs.
3.42's, stock height/wheels.
15 city, 18 highway
73 K2500 Suburban
Stock old ass 350 w/Q-jet. Headers and exhaust. SM465. Weighs 6400 lbs.
4.11's. ~6" lift with 37's.
D60 front, 14 bolt rear.
About 10 mpg combined. The speedo broke a long time ago so that figure is old.
As for the 6 mpg.
A few years ago the '73 'Burb was running like crap and getting about 4 mpg. I decided to do a tune up. I took off the distributor cap and it looked like the internals came off the Titanic. So I replaced the distributor with a new one ($115) and replaced the carb with a rebuilt Jegs Q-jet ($300). Mileage went from 4 to 10. The throttle was also amazingly responsive compared to before. Before I did any mods I once got 14 mpg on a highway trip.
For me the key is not to exceed 2500 rpm on the highway. With the 4.11s and 37s that's about 65 mph so it's cool. I have to hit 3100 rpm to go 75 and it absolutely swills fuel at that speed so it's not worth it. Can't do much about the town mileage except creep around...
Last edited:
Interesting to see all these mileage figures. I just purchased a 1985 k10 short bed with 35s and 3/4 axles (I would assume 4.10 gears) and its not getting anywhere near 10mpg. I am pretty sure the secondaries are not opening. Literally have to shift down to 2nd gear if there is anything even resembling and incline. Im guessing around 5 mpg... I can watch the gauge drop.
6.2 n/a
83 K10 (in stock form)
mechanical injection
6.2 c-code with about 135K
700R4
3.08 with 235/75R15 (~1400RPM@55MPH, ~1700RPM@65MPH, )
This truck won't win any drag races, but after about 15,000 miles of driving I was expecting 21-22 MPG at 65 MPH, 22-24 MPG at 55 MPH, and 18-20 in town (lightly loaded).
It's not a great candidate for hauling loads (the downside of 1400RPM
). Trailering on the highway, even here in the midwest, requires downshifting on anything more than a gentle slope. Mileage drops accordingly. I think I got 15MPG hauling a full load and a 2k pound trailer on my last roadtrip.
I recently swapped my c-code intake for a 6.5L intake (no more plug in my intake
). Mileage has risen, black soot has dropped, and I'm downshifting less often. Power-wise, it's almost up to the level of a normal truck. 
But I only have ~1000 miles' worth of data so far. We'll see what the average is after a few more thousand miles.
83 K10 (in stock form)
mechanical injection
6.2 c-code with about 135K
700R4
3.08 with 235/75R15 (~1400RPM@55MPH, ~1700RPM@65MPH, )
This truck won't win any drag races, but after about 15,000 miles of driving I was expecting 21-22 MPG at 65 MPH, 22-24 MPG at 55 MPH, and 18-20 in town (lightly loaded).
It's not a great candidate for hauling loads (the downside of 1400RPM
). Trailering on the highway, even here in the midwest, requires downshifting on anything more than a gentle slope. Mileage drops accordingly. I think I got 15MPG hauling a full load and a 2k pound trailer on my last roadtrip.I recently swapped my c-code intake for a 6.5L intake (no more plug in my intake
). Mileage has risen, black soot has dropped, and I'm downshifting less often. Power-wise, it's almost up to the level of a normal truck. But I only have ~1000 miles' worth of data so far. We'll see what the average is after a few more thousand miles.
Last edited:
The 6.2 in my 82 GMC is lucky to get 15 mpg period...the extreme cold no doubt reduces the fuel efficiency a lot,I dont drive it far either,only 5-10 miles at a time,so each start up is a cold one...it doesn't use much fuel running it at light throttle plowing my driveway,a good half hour's use probably sucks a gallon down,thats not too bad considering a cold start and heavy pushing..
But driving it on the road its a slug,and seems to slurp the fuel down pretty quickly...the TH400 is probably no help,and I dont know what the gears are in it,but they feel pretty high geared for a 3/4 ton,maybe 3.23's or 3.42's?...always feels like its in too high a gear and the torque converter is making up for it,I often pull it down manually into second instead of letting it stay in third..and try not to wind it up much over 2500 rpm,or it'll drink more fuel faster..
4x4 Livin's truck probably is suffering from altitude sickness...you lose a lot of power at high elevation,and you'll have to keep your foot stuffed in it to keep it moving...might check to make sure the secondaries DO open,maybe they are stuck or a vacuum pull off isn't letting them open like they should..advancing the timing might help too,or re-jetting the carb..
But driving it on the road its a slug,and seems to slurp the fuel down pretty quickly...the TH400 is probably no help,and I dont know what the gears are in it,but they feel pretty high geared for a 3/4 ton,maybe 3.23's or 3.42's?...always feels like its in too high a gear and the torque converter is making up for it,I often pull it down manually into second instead of letting it stay in third..and try not to wind it up much over 2500 rpm,or it'll drink more fuel faster..
4x4 Livin's truck probably is suffering from altitude sickness...you lose a lot of power at high elevation,and you'll have to keep your foot stuffed in it to keep it moving...might check to make sure the secondaries DO open,maybe they are stuck or a vacuum pull off isn't letting them open like they should..advancing the timing might help too,or re-jetting the carb..
xenomarine
1/2 ton status
84 Blazer -
when it was stock:
stock 305/700r4/half ton 2.73's/31's - ~9 mpg
first major surgery:
freshened up 355 w/ mild towing cam/half blown up 700r4/3/4 ton 4.10's/35's - ~11 mpg
when i ****ed it all up:
400hp crate 355/1 ton 4.56's/38.5's - 4-5 mpg
All combos had the same qjet, but tuned to the motor. The last mpg is so low partially because I love the sound of it and just get into it way too much.
87 k10 -
tbi 350/th400/1/2 ton 3.42's?/35's - ~12 mpg
76 C30 CCLB
qjet 454/th400 w/ US Gear underdrive/4.10 14 bolt - 13-15 highway cruising mileage
This thing cruises on the highway at 60-65, around town mileage kills it though especially stop and go.
when it was stock:
stock 305/700r4/half ton 2.73's/31's - ~9 mpg
first major surgery:
freshened up 355 w/ mild towing cam/half blown up 700r4/3/4 ton 4.10's/35's - ~11 mpg
when i ****ed it all up:
400hp crate 355/1 ton 4.56's/38.5's - 4-5 mpg
All combos had the same qjet, but tuned to the motor. The last mpg is so low partially because I love the sound of it and just get into it way too much.
87 k10 -
tbi 350/th400/1/2 ton 3.42's?/35's - ~12 mpg
76 C30 CCLB
qjet 454/th400 w/ US Gear underdrive/4.10 14 bolt - 13-15 highway cruising mileage
This thing cruises on the highway at 60-65, around town mileage kills it though especially stop and go.
If the secondaries weren't opening, your mileage would be great.
Your MPG is based off of GPS or some other proven mileage measuring device?
MrSchaeferPants
1/2 ton status
82 Blazer
6.2 c-code
700r4
np208
1/2 ton 3.08
33" a/t
17mpg city/rural mix (not sure the rural part is better/worse/the same as city with the hills/bends/turns/slowing down/speeding up), interior stripped, no topper on. Never took it on the highway. I'll be interested to see when I get the J code on, and finish my 3/4 ton 3.73 swap.
6.2 c-code
700r4
np208
1/2 ton 3.08
33" a/t
17mpg city/rural mix (not sure the rural part is better/worse/the same as city with the hills/bends/turns/slowing down/speeding up), interior stripped, no topper on. Never took it on the highway. I'll be interested to see when I get the J code on, and finish my 3/4 ton 3.73 swap.
Maybe the secondary butterflies open,but the air valve doesn't,so it dumps raw gas in the rear barrels-- but doesnt get enough air to let it burn efficiently?..
hillbilly deluxe
Professional Pile-It
A single cab short bed should scoot around just fine with any HEALTHY V8 Gm put in it. If my heavy ass '73 can get 10mpg I'd think your '85 could do a little better. I'd start looking for maintenance items. Like you said, carb, but also plugs, wires, air filter etc.
I just got a job with a guy I used to work for. He gave me a '97 K3500 extended cab long bed Chevy with a 454. I'm guessing it's got 4.11's since it was at like 2500 on the highway. It's the same way. SES light is on and it has no power. A 454 shouldn't downshift on little bitty hills. It needs work. No idea what the mileage is yet, I'm using it for a service truck and it sits a lot.
Even with my choke staying closed? I am seriously down on power.... Havent driven the truck enough to know the true mpg... it will be gps based. I need to get this choke staying closed thing fixed first. I believe its the oil pressure sender that goes to the choke what is causing my issue.
Ya, I just bought it and got a good deal on it. The choke light is staying on. I have done a bunch of research on here and am pretty sure that I need to replace the oil pressure sensor that sends signal to the electric choke. I will be replacing that today or tomorrow. Truck runs great, just seriously down on power and sucking gas down. If I get this choke issue fixed before the weekend, I am going to take it wheeling this weekend!!!!!
hillbilly deluxe
Professional Pile-It
Let us know how it goes. Never owned an '85 so I know nothing about the electronics of that vintage. 
85 Blazer
GM Goodwrench 350 with Comp 4x4 cam
M4ME Quadrajet
Headers and duals
4.10 gears and 33's
4 inch lift
3/4 Ton axles
11-13 in town (Gets moving real easily, love that torquey cam)
15 max on Hwy.
GM Goodwrench 350 with Comp 4x4 cam
M4ME Quadrajet
Headers and duals
4.10 gears and 33's
4 inch lift
3/4 Ton axles
11-13 in town (Gets moving real easily, love that torquey cam)
15 max on Hwy.
choke should just have a keyed 12v going to it and a ground.... that's it.
