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1490 Views 14 Replies 9 Participants Last post by  Method2Madness
So, I've spent the past hour searching and mulling through the site trying to get a solid answer, but have come up a bit short.

I just bought a 2011 Colorado 2.9l, 4sp auto ext cab on stock tires. Only mods are k&n cai and some weird sounding magnaflow exhaust. I have a bed cover also. The truck is in mint condition, runs perfectly and has been well maintained as far as I can tell. 68,500 miles.

The issue im having is with fuel mileage. Im thinking its a bit low. I've gone 150 miles and am right at half a tank. I've run the ac/defrost a bit and the transmission gearing on this thing is a bit wonky, so sometimes you have to get on it to make it downshift in order to maintain 70mph. Given this, does 150 miles on half a tank sound a bit low to you guys?

What are you with the 2.9 seeing at half a tank?

I know from my search, mpg is a hot topic and I'm not trying to beat a dead horse. I'm just a bit concerned as I have a 30 day, 100 percent warranty, and 3yr/36000 mile warranty after that, and if something's wrong, I wanna get it looked at by one of the techs at work (I work for the dealership where I bought it)

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If the tank was full how many gallons of gas have you used? Guy I work with has a 2010 truck that looks like yours and he said it gets 2O in town and 24-25 on the hiway. He also drives it hart. So that's not bad but stil there are a lot of variables that make mpg vary.
your gas gauge is not an accurate reading for fuel mileage. drive until you need to fill up, crunch the numbers and get back to us.
As the others have said, you need a more accurate mpg reading. At the next fill set the trip meter to zero. Then when you fill again, note the mileage traveled and the amount to fill up. Divide the miles by the number of gallons and that will give you a better indication of your mileage.
Also compare the tire size installed on your truck matches the factory installed option. Factory size is listed on the manufacturer label located on the driver side door jamb.

As mentioned above, please calculate your mileage based on used gallons and distance travelled. If tires are not factory size you won't get accurate readings.

Otherwise, what you are experiencing seems pretty normal/reasonable.

My 3.7l averages between 15.8 and 16.1 due to oversized tires. That's like 225 between fillups if I take it low.
Thanks for the responses!

I was already planning on doing the mileage calculations as you've all suggested, as I know the gauge isn't always the best indicator. But even if the gauge is a little off, 160 still seemed a bit odd, so I wanted to get a rough idea of what others were experiencing.

I'll definitely do the calculations and report back.

Thanks again for the help. :)
Purchased my 2012 truck in August of this year and I’m seeing 19.7+ in the city, 22-23 hwy. At ¾ = 100 miles, 1/2 = 199 miles, ¼ = 280+ miles. I let the pump click 2 times, (from past experiments with 3 clicks, the 2nd and 3rd times are usually no more than .2 tenths of a gallon i.e. 14.2 then 14.4). I also found that premium gives more consistent mpg’s all around taking in to account stop/go traffic, short errands to the store and adverse weather conditions. i might get flamed for this, but I think the full CIA and free flow exhaust is hurting more than helping. Two things that improved my mpgs were new plugs and TB clean, but the truck only had 24k miles in 4 years time. At 160 miles and ½ tank, I’m guessing high 17’s at fill-up.


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My 2.8 gets 26 mpg.... 5 speed 4 wheel drive.
I get over 400 miles outta a tank of fuel... Running reg. 87 octane....
So, i just put in a can of seafoam, filled up and changed the spark plugs (Bosch platinums) out for AC delco iridiums. I've noted the mileage and will do the calculations at next fill up.

Thanks again, all for the info and assistance!

Newcoly and Tweek: Thanks! Your posts give me a rough estimate.

Also, I tend to agree with you about the CAI and exhaust. Both are more than likely going away as soon as I can find a stock airbox and associated hardware, and can swing by to pick up the stock exhaust from a most generous donor. :)
My '09 2.9 Auto (Reg cab) gets between 22-24 mpg. I have noticed it gets a little better with the AC off and goed down at any speed faster than about 68 Mph. That seems to be the sweet spot (rpms At or below 2000).

I do notice that depending on the angle of the truck at fillup time (front facing up hill) that I can get as much as 120 miles on the top 1/4 of the tank, but usually at 100 miles. If I had to fill it up level, I only get 80 miles on the top 1/4 of the tank. I typically get between 380-410 miles per tank.
Good move going with the Delco plugs. As long as you didn't attempt to gap the plugs.

Seafoam - don't expect magic. All that will do is maybe clean injectors a tad.
Good move going with the Delco plugs. As long as you didn't attempt to gap the plugs.

Seafoam - don't expect magic. All that will do is maybe clean injectors a tad.
Nope. No gapping. :)

And I don't expect the seafoam to do a whole lot. But figured it wouldn't hurt.
At a preliminary glance, it appears the plugs are doing the trick. I've driven 75 miles and still halfway between full and 1/4. I'm still going to do the actual mpg math, tho.

Also, spoke with the original owner and he is going to be bringing me the stock exhaust and airbox on Thursday, which I more than likely will be reinstalling in place of the k&n and magnaflow.
2012 Crew cab Z71 4x4
5.3l auto 4.10 gears
265/65 R18 tires

Volant CAI
Supermodulation PTB
Custom cat back exhaust 1 in 2 out Magnaflo
Diablo intune running economy tune (getting lined up for supermod remote tune)

Fill up with Shell 87
full to 3/4 - 100 miles
3/4 to 1/2 - 100 miles
1/2 to 1/4 - 95 miles
1/4 to 1/8 - 20 miles

16.416 gallon needed to top off = 19.188 MPG

Mileage was 70 percent Highway running 70 to 75 (speed limit 65 to 70) running 5 over.
30 percent city 35 to 55 with a lot of red lights.

Can't complain
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So, I crunched the numbers, and with combined city/hwy driving, I'm at like 20.7mpg. I was right at 200 miles at half a tank, as well. So, it looks like after the plug change, I'm right inline with what most are reporting on the site.

Thanks for all your help!
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