Mileage

coreylubahn · Post by **coreylubahn** » Thu Dec 02, 2004 11:50 am

So what kind of gas mileage does everyone get. I have done the air-box mod and put in a K&N and I also have a topper on the back, but I only get around 15 City and maybe 17 Highway (Maybe only 16). I would have thought the airbox mod and K&N would have helped but they didn't make much, if any difference. I always run 89 Octane (with Ethanol here in Iowa). Just seems to me that the mileage is really low. Would a new exhaust system help any...maybe I can convince the money manager (also known as my wife) to let me spend some money if there is some return to be had (as in better gas mileage). I don't know....I love the truck but the mileage stinks!!!

jeff024 · Post by **jeff024** » Thu Dec 02, 2004 12:05 pm

welcome to the site .......... i get right around 19.5-21 mpg i also mainly drive highway miles so i may be on the high end and all i have done is the air intake , exaust and a bed cover.

coreylubahn · Post by **coreylubahn** » Thu Dec 02, 2004 12:14 pm

Thanks for the welcome...I've been lingering in the darkness for almost a year now just reading posts and looking at the modification info, but I thought it was time for me to start joining in.

Anyway, 19.5-21....wow....not even since new have I ever had even 20 (heck I can't remember even 19) when running a complete tank through on all highway. My mileage doesn't seem to change that much going city to highway, only a couple MPG if that. I'm not sure I have ever had the odometer past 255 miles on a single tank....most times I'm lucky if I get to 235. What the heck!!!

jeff024 · Post by **jeff024** » Thu Dec 02, 2004 12:20 pm

i usually stop for gas when it hits 295-300 and put 15 gals in the tank and always fun 89octane and when on highways i run 65-80mph so its not like im easy on it i guess i just hit the top end i also make sure all fluids are changed when the miles permit . i think the intake helped and the bed cover not sure the exaust did that much but noise and maybe a bit more pickup.

barch97 · Post by **barch97** » Thu Dec 02, 2004 12:22 pm

try using your cruise control more. and slow down. keeping the tach under 2000rpms will have a dramatic effect on your fuel economy.

Retep · Post by **Retep** » Thu Dec 02, 2004 1:00 pm

coreylubahn wrote:...I've been lingering in the darkness for almost a year now just reading posts and looking at the modification info, but I thought it was time for me to start joining in.

Come on in... the water's fine

Welcome to the site.

If enough people chime in on this, I think you will find that mpg rates are all over the place with more being in the lower numbers.
I used to average 18.5 mpg or so with a 50/50 mix of city and highway driving. I have even seen 22 -23 mpg on long highway trips. But those days seem to be long ago. I have been fighting a mileage problem for a couple months know. currently averaging 17 - 17.5 mix. I have no idea if I have fixed my problem or not because now it is cold here and I believe we have switched to winter formula gas (both mileage killers).

coreylubahn · Post by **coreylubahn** » Thu Dec 02, 2004 1:01 pm

I usually use my cruise religiously on road trips...if I don't I end up going 25/30 miles over (these trucks really move without feeling like it). Am I the only one that has this kind of mileage....I mean 300 on a 15 gallon tank is 20 MPG...Best I think I've ever had is like 18 on a road trip with the cruise set at 75 or 80...must be the RPMS....cause at my highway speed I never get below 2000. Interesting and informative....thanks guys!!

jeff024 · Post by **jeff024** » Thu Dec 02, 2004 1:05 pm

what rear gear do you have i have 3.73s?

Retep · Post by **Retep** » Thu Dec 02, 2004 1:06 pm

coreylubahn wrote:I mean 300 on a 15 gallon tank is 20 MPG...

Crew cabs only have a 15 gallon tank??? I have a 19 gallon tank.

jeff024 · Post by **jeff024** » Thu Dec 02, 2004 1:10 pm

no retep we have a 17.5 gal tank

coreylubahn · Post by **coreylubahn** » Thu Dec 02, 2004 1:13 pm

jeff024 wrote:what rear gear do you have i have 3.73s?

I really don't know...I have a stock truck except what's listed in my signature, and 3.73 is stock is it not. Also, the absolute most gas I have ever stuck in my truck was like 15.5 gallons and the needle just about broke off...I'm going to have to go home and look at the window sticker and check out the tank capacity.

barch97 · Post by **barch97** » Thu Dec 02, 2004 1:15 pm

coreylubahn wrote:Best I think I've ever had is like 18 on a road trip with the cruise set at 75 or 80...

that'll do it. try running a tank at around 65-70. and yes the gear ratio will make a big difference there also. the 3:42 will do better on gas where the 3:73 delivers more power.

I've got 3:73 and have never gotten better than 19mpg. more typically around 17mpg.

barch97 · Post by **barch97** » Thu Dec 02, 2004 1:18 pm

coreylubahn wrote:
jeff024 wrote:what rear gear do you have i have 3.73s?
I really don't know...I have a stock truck except what's listed in my signature, and 3.73 is stock is it not. Also, the absolute most gas I have ever stuck in my truck was like 15.5 gallons and the needle just about broke off...I'm going to have to go home and look at the window sticker and check out the tank capacity.

More common to have 3:42 in an '03. check your glove box rpo codes to be sure.

G80 Axle Positraction Limited, Slip

GT4 Axle Rear 3.73 Ratio (Dup with 5X1)

GT5 Axle Rear 4.10 Ratio (Dup with GT8)

GU4 Axle Rear 3.08 Ratio

GU6 Axle Rear 3.42 Ratio

Retep · Post by **Retep** » Thu Dec 02, 2004 1:20 pm

Barch is correct. anything above 70 mph and mileage drops off fast.
I have 3.73 gears.

coreylubahn · Post by **coreylubahn** » Thu Dec 02, 2004 1:38 pm

I'll have to check my RPO codes, but I'm fairly certain that I got the posi with the 3.73 gears when I got my truck. At least now I don't feel alone in the world that there are others that get close to the same mileage as me. I just started hearing 20...21 and started wondering what was up...must be gearing and speed choice. So now I know. Thanks all for your responses.

Rusty · Post by **Rusty** » Thu Dec 02, 2004 1:45 pm

Hi Corey! Welcome to the site!

Our CrewCab has 3.73 gears and when I was driving it, the gas mileage was pretty bad (12-15 range combined hwy/cty), but then I have a lead foot. My wife drives all the time now and she is much nicer to it than I was so I'm sure the mileage has improved quite a bit. I'll have to check it sometime.

Ken · Post by **Ken** » Thu Dec 02, 2004 7:18 pm

I took a trip a few weeks ago (Approx 260 miles round trip) a large percentage of that was on interstate and over some fairly good sized mountains. I drove 75 -80 MPH the entire trip and there was a small amount of city driving. Round trip though I got 19.2 MPG. I have stock ZR5 wheels and tires (Goodyears) 3.73 gears, and I just recently (July) changed all fluids out to full synthetic. Eng, Trans, Diffs, & Transfercase.

Welcome to the Forum.

jeff024 · Post by **jeff024** » Fri Dec 03, 2004 2:53 am

mid 19s per gal is what i average . Finally someone else who get more then 17-18 and my trucks the same as yours Ken just no Z wheels .And i have never used anything other then synthetic , cost a bit more but i dont change it as often and hopefully it will be better in the long run.

Jim · Post by **Jim** » Fri Dec 03, 2004 4:56 am

With the last two tank fulls I have broken the 20 MPG barrier (barely). Both tanks were mostly Highway 65-70 MPH.

Post by **HenryJ** » Fri Dec 03, 2004 6:20 am

HenryJ wrote:My worst mileage was 14.1 mpg, Best mileage 22.8 mpg

Average of 39 fill-ups , 16.89 mpg

Like everyone else I am usually between 15-18 mpg normally. With extended offroading it hovers at or just below 15 mpg.

Gas Mileage

Welcome

Jeff · Post by **Jeff** » Tue Jan 04, 2005 12:21 pm

Starting out, I was getting between 21 and 22 miles per gallon, bone stock, using synthetic oil and changing every 3,000 miles. I got to the point of getting about 14 to 15 mpg around 45,000 miles. I did a full tune up, cap, rotor, wires and plugs (Plugs were burnt bad) and am back to 21, 22 mpg.

kf6kmx · Post by **kf6kmx** » Tue Jan 04, 2005 9:55 pm

Jeff wrote:Starting out, I was getting between 21 and 22 miles per gallon, bone stock, using synthetic oil and changing every 3,000 miles. I got to the point of getting about 14 to 15 mpg around 45,000 miles. I did a full tune up, cap, rotor, wires and plugs (Plugs were burnt bad) and am back to 21, 22 mpg.

Really? What plugs did you put in it?
I have just coming up on 42k.. I'm also down to about 15 to 16mpg from a 18-20 past avg.. But I also changed my tires (size/type) which I figure is affecting me a little at least.
I didnt think it would be needing plugs this soon, but it might be worth a check (I guess I'm spoiled by my girlfriend's that came with the 100,000 mile spark plugs in it

)
I know we have 100k anti-freeze, but I never looked up the avg life of the plugs..

Fish4Fun · Post by **Fish4Fun** » Wed Feb 09, 2005 10:37 pm

Hay everyone just found site and just picked up a 2003 ZR5 crew cab.
I got it about 2weeks ago and have been watching the gas mileage. Its just like my 99 gmc jimmy with the 4.3 on side note my jimmy started dropping off on gasmileage at around 45k then i rolled it at 53k and got the truck

I am looking at the original window sticker for mine (guy took great care of this truck only had 9k on it)

i have 3.42 axle
235/70R15 goodyears
17.5 gallon tank
i am avg just over 20mpg but i drive main interstate set on cruise at 69 35 miles one way to work and then back. i usually fill up after 230 miles and it takes 11 gallons. and i have 1/4 tank left on gauge.

the window sticker says 15 city 19 highway
fine print says EPA indicates that the majority of vehicles will achieve
12 and 18 in the city and between 16 and 22 on highway

with an annual fuel cost of $1367

Post by **HenryJ** » Thu Feb 10, 2005 8:29 am

Fish4Fun wrote:.... my jimmy started dropping off on gasmileage at around 45k....

Might be worth looking into a tune-up around that mileage. Check the plugs, and probably replace the cap, rotor, and stock plug wires.

killian96ss · Post by **killian96ss** » Thu Feb 10, 2005 9:53 am

HenryJ wrote:
Fish4Fun wrote:.... my jimmy started dropping off on gasmileage at around 45k....
Might be worth looking into a tune-up around that mileage. Check the plugs, and probably replace the cap, rotor, and stock plug wires.

I'm about to do the plug wires with a new cap & rotor, and I currently have 48k miles. I thought our plugs were the 100k mile platinums?? Almost every GM vehicle since 1996 that I have worked on had the platinums. Did GM give us the crappy plugs to cut more costs?

Steve

top_sgt · Post by **top_sgt** » Thu Feb 10, 2005 11:45 am

noooooooooooo...GM wouldn't do that!!!

just look at the stocks,, ball joints,,............

Post by **HenryJ** » Thu Feb 10, 2005 12:33 pm

killian96ss wrote:
HenryJ wrote:... Check the plugs...
... I thought our plugs were the 100k mile platinums?? ...

They are rated for up to 100k. Check the plugs they will show signs of other problems like leaky injectors , rich/lean , additive fouling , etc.
They may even need replacement. At 50k you are halfway through the useful lifespan, things may not be operating at peak levels.

killian96ss · Post by **killian96ss** » Thu Feb 10, 2005 9:41 pm

HenryJ wrote:They may even need replacement. At 50k you are halfway through the useful lifespan, things may not be operating at peak levels.

I wonder if it would be worth it to upgrade to the AC Delco Raipid Fires, Denso Iridiums, or something simular? Depending on the vehicle sometimes the stock plugs work best.

I've had to learn the hard way about spark plug hype over the years with several different vehicles.

Steve

Post by **HenryJ** » Fri Feb 11, 2005 8:39 am

killian96ss wrote:...I wonder if it would be worth it to upgrade to the AC Delco Raipid Fires, Denso Iridiums, or something simular?...

The stock plugs are pretty good and unless there is a problem, I'd run them out.

I switched to NGK Irridium's since I am running the MSD. They are working really well, but are pricey!

There is a thread on sparkplugs around here somewhere. I tried the Bosch Plat.+4. They didn't work out so well.

killian96ss · Post by **killian96ss** » Fri Feb 11, 2005 9:32 am

HenryJ wrote:I tried the Bosch Plat.+4. They didn't work out so well.

I tried these on my SS and they caused idle problems, and surging at certain speeds. It seems to me that some of these fancy plugs work better on the old carbureted muscle cars than the current fuel injected computer controlled cars.

Since I have been getting a little off topic, I average 16-18 mpg city/hwy, with the 3.73's, BL, and 31's. Only 1 time did I get 300 miles out of one tank, and this is when my truck was still new with no BL or 31" tires.

Steve