better gas mileage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

carter442 · 10-04-2009, 12:44 PM

i have an 88 k2500 6 lug 3/4 ton. it has a 700r4 and a 350 tbi 3.42 gears. my fuel gauge doesnt work so i estimate my economy at 10 mpg so i dont run out but when i decided to go up a bit to se what im really geting i went to 13 mpg and ran out of gas when i should have had 3 gallons in my truck. i dont rev more than 2000 rpm on acceleration and at cruising at 50 to 55 im reveing about 2100 to 2200. iv seen people with these exact same conditions that are gtting close to 20 mpg i drive 27 to 28 miles a day an only 2 of them are in the city the rest are in the country or highway any ideas why my gas mileage is horrible?

ChevLoRay · 10-04-2009, 03:15 PM

Lots of things affect fuel mileage, not the least of which is the appointed masher of the gas pedal. Beyond that, it's things like stop and go driving, rapid acceleration and braking, poor engine condition, slipping transmission components, and the list goes on and on.

It could be as simple as a thermostat that is rated at too low a temperature which then allows for a cooler coolant temp that doesn't compute with the electronic inputs to the CPU, and subsequently enriches the air/fuel mixture. A richer mixture is then read by the O2 sensor and that means another adjustment to the fuel system.

It's kinda hard to diagnose like this. Maybe some others will generate a list of stuff to check.

Spray-Bomb · 10-04-2009, 03:25 PM

If you are twisting that kinda RPM at 55, then your trans is slipping bad or you have really short tires

Or, somebody changed the rear gears

Mine cruises at 65 and 70 at those RPM, and has 3:73s with 29" tall tires

ChevLoRay · 10-04-2009, 03:46 PM

At 45MPH, my 3.43 geared V6 is rolling at less than 1500 RPM's. On the highway, 65MPH is less than 2000RPM. The tires I am running are "short" so my speedometer reading is optimistic, too. An indicated 35MPH, is actually 33MPH, per the PoPos' speed monitor strapped to a street sign post.

brawley · 10-10-2009, 10:00 PM

just my 2 cents..but I changed out my catalytic converter,my old one was getting clogged up, my fuel milage went from 10-11 to 14mpg and this is all in town driving.

10-04-2009, 12:44 PM	#1
carter442 Registered User Join Date: Aug 2009 Location: tipton IN Posts: 156	better gas mileage i have an 88 k2500 6 lug 3/4 ton. it has a 700r4 and a 350 tbi 3.42 gears. my fuel gauge doesnt work so i estimate my economy at 10 mpg so i dont run out but when i decided to go up a bit to se what im really geting i went to 13 mpg and ran out of gas when i should have had 3 gallons in my truck. i dont rev more than 2000 rpm on acceleration and at cruising at 50 to 55 im reveing about 2100 to 2200. iv seen people with these exact same conditions that are gtting close to 20 mpg i drive 27 to 28 miles a day an only 2 of them are in the city the rest are in the country or highway any ideas why my gas mileage is horrible?

10-04-2009, 03:15 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: better gas mileage Lots of things affect fuel mileage, not the least of which is the appointed masher of the gas pedal. Beyond that, it's things like stop and go driving, rapid acceleration and braking, poor engine condition, slipping transmission components, and the list goes on and on. It could be as simple as a thermostat that is rated at too low a temperature which then allows for a cooler coolant temp that doesn't compute with the electronic inputs to the CPU, and subsequently enriches the air/fuel mixture. A richer mixture is then read by the O2 sensor and that means another adjustment to the fuel system. It's kinda hard to diagnose like this. Maybe some others will generate a list of stuff to check. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

10-04-2009, 03:25 PM	#3
Spray-Bomb Texas Big Wig Join Date: Jan 2007 Location: Mineola, Texas Posts: 5,620	Re: better gas mileage If you are twisting that kinda RPM at 55, then your trans is slipping bad or you have really short tires Or, somebody changed the rear gears Mine cruises at 65 and 70 at those RPM, and has 3:73s with 29" tall tires __________________ Just not low enough... ----------------------------- Sinister Killer Last edited by Spray-Bomb; 10-04-2009 at 03:28 PM.

10-04-2009, 03:46 PM	#4
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: better gas mileage At 45MPH, my 3.43 geared V6 is rolling at less than 1500 RPM's. On the highway, 65MPH is less than 2000RPM. The tires I am running are "short" so my speedometer reading is optimistic, too. An indicated 35MPH, is actually 33MPH, per the PoPos' speed monitor strapped to a street sign post. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. Last edited by ChevLoRay; 10-04-2009 at 03:48 PM.

10-10-2009, 10:00 PM	#5
brawley Easy Does It Join Date: Apr 2007 Location: Dirdy Mo , North Carolina Posts: 450	Re: better gas mileage just my 2 cents..but I changed out my catalytic converter,my old one was getting clogged up, my fuel milage went from 10-11 to 14mpg and this is all in town driving.



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