Why My 350 is poor MPG on Gas??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lost_66 · 02-08-2005, 03:07 AM

i want to know why my 82 chevy c/20 engine 350 with SM465 and has bad mileage on gas... i fill up gas for 20 gallion tank cost me almost $30 doller
and i drove on hwy only 65 mph and 2 hour and 15 min later it goes to empty in tank! i figure it was not 17 mpg.. and i dont understand why my engine so bad on gas but there no missing sound and has new tune up wire, spark plug and do you have idea why my engine has bad mpg gas??

gchemist · 02-08-2005, 03:56 AM

What is the tire size and rearend gear ratio? Do you have a tach? What is the basic timing? Does it have emission equipment on it? Has the cat ever been replaced?

CbHeEaVsYt · 02-08-2005, 04:07 AM

has it been real cold there lately?
cause in cold weather u usually get crappy mrg

79Silv4x4 · 02-08-2005, 10:00 AM

First I would check the ACTUAL fuel mileage. The fuel gages in these trucks are not kown for their accuracy so don't rely to heavily on what it says. Once you know what the actual mileage we can tell if it's really all that bad. . .

lost_66 · 02-08-2005, 02:12 PM

Quote:

Originally Posted by gchemist

What is the tire size and rearend gear ratio? Do you have a tach? What is the basic timing? Does it have emission equipment on it? Has the cat ever been replaced?

my rearend gear ratio dont know what is ratio? and i dont have tach timing is "4" with 800 rpm there no emission equipment and no cat only dual exhaust with glass pack and tire size is 235/85/16 not wide tires..

SCOTI · 02-08-2005, 06:21 PM

My stock 74 350ci, 2-barrel, turbo 350, 12-bolt w/3.40's, & 29" tall rear tires get a whopping 10mpg city/hwy combined.

My 68 6cyl, 250ci, 1-barrel, 3spd manual, 12-bolt w/3.73's & 28" tall tire got a whopping 12mpg city/hwy combined.

Define crappy milage.

*1FaastC10* · 02-08-2005, 07:09 PM

my K20 350/350 4.10s and 31" tires gets 12 mpg with an 8' Western blade hanging on the front of it.

lost, sounds to me like she's begging for a tuneup.

lost_66 · 02-08-2005, 08:44 PM

i put new tune up before..

EGK v power and accel spark plug wire, blue straek dist and rotor cap

but still not improve mpg.. do you think carb would need tune right?
or something?

*1FaastC10* · 02-09-2005, 01:11 AM

25 year old truck, it may need tuned, rebuilt, or trashed and replaced.

DirtyBurb86 · 02-10-2005, 11:37 AM

Don't feel so bad, I'm getting about 5 MPG in my '86 burb.

-Shawn

TrainD5115 · 02-10-2005, 01:01 PM

I can tell you that I went from about 12 mpg down to about 7 mpg because of a vacuum leak and a stuck choke. I'm still trying to find it and its time consuming because of all the extra vacuum lines my setup has.

72402 · 02-10-2005, 10:56 PM

If I had an 82 3/4 ton with a 350 that was getting anywhere close to 17 mpg, I'd be braggin about it. My 72 1/2 ton with 402 will get maybe 10 on a good day.

Tom · 02-11-2005, 05:22 PM

My vortec 350, 2004R overdrive, 3.07 rear, non emissions 79 with 27" tires gets a whopping 15mpg on the freeway, still a crappy 10mpg around town, and thats with a roller cammed vortec headed efficiant motor. These trucks just don't have the aerodynamics to get good milage.

02-08-2005, 03:07 AM	#1
lost_66 Registered User Join Date: Nov 2003 Location: Pillager,MN Posts: 181	Why My 350 is poor MPG on Gas??? i want to know why my 82 chevy c/20 engine 350 with SM465 and has bad mileage on gas... i fill up gas for 20 gallion tank cost me almost $30 doller and i drove on hwy only 65 mph and 2 hour and 15 min later it goes to empty in tank! i figure it was not 17 mpg.. and i dont understand why my engine so bad on gas but there no missing sound and has new tune up wire, spark plug and do you have idea why my engine has bad mpg gas??

02-08-2005, 04:07 AM	#3
CbHeEaVsYt Pick up man Join Date: Feb 2005 Location: trenton mi Posts: 135	has it been real cold there lately? cause in cold weather u usually get crappy mrg __________________ heres sum pics of my truck 82 silverado c10 heres my baby 1990 k1500 check out this 1957 chevrolet for sale

02-08-2005, 06:21 PM	#6
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,071	My stock 74 350ci, 2-barrel, turbo 350, 12-bolt w/3.40's, & 29" tall rear tires get a whopping 10mpg city/hwy combined. My 68 6cyl, 250ci, 1-barrel, 3spd manual, 12-bolt w/3.73's & 28" tall tire got a whopping 12mpg city/hwy combined. Define *crappy* milage. __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

02-10-2005, 01:01 PM	#11
TrainD5115 North Coast, baby! Join Date: Jun 2004 Location: Toledo, OH Posts: 437	I can tell you that I went from about 12 mpg down to about 7 mpg because of a vacuum leak and a stuck choke. I'm still trying to find it and its time consuming because of all the extra vacuum lines my setup has. __________________ Brad 79 Scottsdale C20 350/350 3.73's Still running full CA smog gear!

02-10-2005, 10:56 PM	#12
72402 Registered User Join Date: Nov 2004 Location: Cameron, Oklahoma Posts: 199	Gas mileage If I had an 82 3/4 ton with a 350 that was getting anywhere close to 17 mpg, I'd be braggin about it. My 72 1/2 ton with 402 will get maybe 10 on a good day.

02-08-2005, 03:56 AM	#2
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	What is the tire size and rearend gear ratio? Do you have a tach? What is the basic timing? Does it have emission equipment on it? Has the cat ever been replaced?

02-08-2005, 10:00 AM	#4
79Silv4x4 Workaholic Join Date: Oct 2002 Location: Katy, TX Posts: 1,589	First I would check the ACTUAL fuel mileage. The fuel gages in these trucks are not kown for their accuracy so don't rely to heavily on what it says. Once you know what the actual mileage we can tell if it's really all that bad. . .

02-08-2005, 07:09 PM	#7
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	my K20 350/350 4.10s and 31" tires gets 12 mpg with an 8' Western blade hanging on the front of it. lost, sounds to me like she's begging for a tuneup.

02-08-2005, 08:44 PM	#8
lost_66 Registered User Join Date: Nov 2003 Location: Pillager,MN Posts: 181	i put new tune up before.. EGK v power and accel spark plug wire, blue straek dist and rotor cap but still not improve mpg.. do you think carb would need tune right? or something?

02-09-2005, 01:11 AM	#9
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	25 year old truck, it may need tuned, rebuilt, or trashed and replaced.

02-10-2005, 11:37 AM	#10
DirtyBurb86 Narcissistic Prick Join Date: Dec 2004 Location: So Cal Posts: 87	Don't feel so bad, I'm getting about 5 MPG in my '86 burb. -Shawn

02-11-2005, 05:22 PM	#13
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	My vortec 350, 2004R overdrive, 3.07 rear, non emissions 79 with 27" tires gets a whopping 15mpg on the freeway, still a crappy 10mpg around town, and thats with a roller cammed vortec headed efficiant motor. These trucks just don't have the aerodynamics to get good milage. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.



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