Z code engines - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Boog** · 02-01-2012, 09:55 PM

I just bought a 2006 GMC crew Z71. It has the 5.3 Z code engine. According to the owners manual it is a flex fuel engine. It does not have the FlexFuel emblem on the tailgate but that doesn't mean anything.
While E85 is not readily available in our part of the country yet I am curious how these trucks run on it.
Anyone use E85 much and have real world comparison results to regular unleaded gas. Cost and mpg, performance?

1978steven · 02-04-2012, 11:26 AM

My wife's '04 Tahoe is flex fuel with the 5.3. Although we do not regularly run E-85 I can tell you a few things we noticed the few times we have ran it. Here in NY flex fuel is not drastically cheaper then regular unleaded (current prices here in NY $3.08/E-85 and $3.69/Reg Unleaded), I did notice a more peppier driving Tahoe while running E-85, significantly less fuel mileage where she normally averages 14-15 mpg daily driving she got around 12 mpg on E-85, we also noticed while running E-85 the exhaust has a distinctive almost like race fuel smell. For daily use I would not run it as the cost per gallon is not worth it, but if loaded down or towing I would run it because it really felt like it had a good deal more powwwaaa.........

BossHogg69 · 02-04-2012, 02:39 PM

Hey Boog, you can drive down here to Sherwood and get a tank of E85 and find out - there's a Phillips station down here off the Wildwood exit on 67/167 that has it.

biggsteve97 · 02-05-2012, 02:30 PM

I have an 03 Z71 Tahoe with the flex fuel 5.3L and I ran the E85 in it for about 2 weeks last year. Here is what I noticed: No real noticeable difference in power or driveability, it seem to be the same but with a slightly smoother idle. However while it was cheaper per tank(1.99/gal E85 vs 2.95/gal unleaded) the fuel mileage had dropped off so much it was not economically feasible to continue use. We went from 14.5mpg down to 8.5-9.1 mpg, therefore we were filling up more often and just negated the benefits for using E85.

02-01-2012, 09:55 PM	#1
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,655	Z code engines I just bought a 2006 GMC crew Z71. It has the 5.3 Z code engine. According to the owners manual it is a flex fuel engine. It does not have the FlexFuel emblem on the tailgate but that doesn't mean anything. While E85 is not readily available in our part of the country yet I am curious how these trucks run on it. Anyone use E85 much and have real world comparison results to regular unleaded gas. Cost and mpg, performance? __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

02-04-2012, 11:26 AM	#2
1978steven Registered User Join Date: Oct 2004 Location: Currently New Windsor, NY but Texas is home Posts: 332	Re: Z code engines My wife's '04 Tahoe is flex fuel with the 5.3. Although we do not regularly run E-85 I can tell you a few things we noticed the few times we have ran it. Here in NY flex fuel is not drastically cheaper then regular unleaded (current prices here in NY $3.08/E-85 and $3.69/Reg Unleaded), I did notice a more peppier driving Tahoe while running E-85, significantly less fuel mileage where she normally averages 14-15 mpg daily driving she got around 12 mpg on E-85, we also noticed while running E-85 the exhaust has a distinctive almost like race fuel smell. For daily use I would not run it as the cost per gallon is not worth it, but if loaded down or towing I would run it because it really felt like it had a good deal more powwwaaa......... __________________ 2002 Silverado 2500HD LB7 CCSB LT EFI Live by Rob at ATP, Edge CTS Insight DSP 5 control, S&B CAI, PPE boost valve, Pro Fab AIH, AirDog II 165, PPE WIF sensor delete plug, 5" stainless exhaust, Cognito braces & HD tie rods, H2's 315/70 R17 BFG's 2004 Tahoe LT 2006 Silverado Z71 LS 1971 Chevy C10

02-04-2012, 02:39 PM	#3
BossHogg69 motor exploder Join Date: Mar 2009 Location: Pittsburgh, PA Posts: 2,346	Re: Z code engines Hey Boog, you can drive down here to Sherwood and get a tank of E85 and find out - there's a Phillips station down here off the Wildwood exit on 67/167 that has it. __________________ Adam 1969 Chevy CST/10 stepside, DART Big M/TREMEC Magnum Extreme/3.73's w/Detroit Truetrac 1965 Chevy Bel Air Wagon (daily driver), 327/TH350,10 bolt w/3.08's 1961 Chevy Bel Air Sport Coupe, ZZ454/M21/9" rear w/3.50's & Detroit Truetrac 2005 GMC 1500 ccsb 2wd, 6.0L/4L65e/3.73 G80 2006 GMC 2500HD ccsb 4x4, DMax LBZ/Allison 6spd/4.56's w/Detroit TrueTrac Use the SEARCH function on this forum - it is your friend!!

02-05-2012, 02:30 PM	#4
biggsteve97 Registered User Join Date: Jan 2010 Location: Kansas City, Mo Posts: 284	Re: Z code engines I have an 03 Z71 Tahoe with the flex fuel 5.3L and I ran the E85 in it for about 2 weeks last year. Here is what I noticed: No real noticeable difference in power or driveability, it seem to be the same but with a slightly smoother idle. However while it was cheaper per tank(1.99/gal E85 vs 2.95/gal unleaded) the fuel mileage had dropped off so much it was not economically feasible to continue use. We went from 14.5mpg down to 8.5-9.1 mpg, therefore we were filling up more often and just negated the benefits for using E85.



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