Offroad Trailblazers and Envoys

Fuel mileage.

Trailblazer and Envoy related, but not off-road related...

by Shdwdrgn » Tue Apr 15, 2014 2:34 pm

Nice to know somebody is using the gear calculator. You wouldn't believe how much effort it took just to get those color bands to come out right! I was looking at the info because I was afraid changing from 3.42s to 4.10s would make way too much difference in my drivetrain, so I had to see the numbers. Once I saw that my 30.5" tires and 4.10s were only going to change my engine speed by 300rpm but put me squarely in the middle of the 'standard duty' range, I had no reservations about making the swap.
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by HARDTRAILZ » Tue Apr 15, 2014 2:36 pm

Trail X wrote:The drag is related to velocity by a power of 2. So the drag force actually increases by 25% between 85 mph and 95 mph. The difference between 70 mph and 95 mph is a 84% increase in drag.

This is why driving into a 15 or 20 mph headwind can really kill your gas mileage.


This is what I was referencing.

I also was thinking that it may have something to do with my relatively flat bottom due to all the skid plating. With a flat surface to behind the TC, it allows less turbulence underneath and I know that affects mpg.
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by TBYODA » Tue Apr 15, 2014 2:59 pm

HARDTRAILZ wrote:I think you are on to part of it.
Yea knew my idea was a very simplistic. Tire size and gearing is all on what your needs are and MPG is what it is good or bad.

HARDTRAILZ wrote:My lack of speeding much is another big thing.
Yep big factor.
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by navigator » Tue Apr 15, 2014 3:14 pm

HARDTRAILZ wrote:My lack of speeding much is another big thing.

If I take it easy (3.42/32s) and stay around 55mph, I can get around 20mpg via scangauge on 10-15 mile trips.
If I am running interstate running 70-75 I usually get around 17mpg via scangauge.

The speed makes a big difference.
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by Shdwdrgn » Tue Apr 15, 2014 3:22 pm

I know someone once spoke of the drag from the huge void under our rear bumpers, and considered cutting some panels to smooth out the airflow back there, but I never heard if it was ever attempted. Seems like it could be done fairly easy with some sheet-metal, using some bends to keep it rigid. Anyone want to give it a try?
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by HARDTRAILZ » Tue Apr 15, 2014 3:23 pm

Sounds like you are getting pretty good mpg!

Running over 70 is what I meant, since speed limit on interstate here is that.

Drove the same basic trip last night on a 55 mph State Highway on the way there and a 70 mph Interstate on the way back...the roads are parallel and for most part you can see the other. Bout 16 miles each way. Not much difference in mpg, but when I crept up toward 80, I would see the Scangauge start to drop.

I think overall with my setup about 60-65 is the sweet spot where everything locks in and just works well. I am sure everyone is a little different in that aspect.
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by HARDTRAILZ » Tue Apr 15, 2014 3:26 pm

Shdwdrgn wrote:I know someone once spoke of the drag from the huge void under our rear bumpers, and considered cutting some panels to smooth out the airflow back there, but I never heard if it was ever attempted. Seems like it could be done fairly easy with some sheet-metal, using some bends to keep it rigid. Anyone want to give it a try?



Could be part of my good mpg's actually. With my rear bumper tucked up tighter all the way around I may not have as big of air dam on the tail-end.

Sheet-metal with bends made me think of pole barn siding/roofing. Might be a cheap option if someone wanted to try it out.
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by Trail X » Tue Apr 15, 2014 4:46 pm

The most streamlined shape known to man is a teardrop that is round up front and tapers off at the rear. So, I could see a lower rear roof or a higher rear bumper being potentially helpful in that regard.

Probably the worst things we can do for our wind resistance is a tall roof rack or a brush guard. Round bars or square bars are some of the worst for drag coefficients.
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by BowTide » Tue Apr 15, 2014 6:25 pm

Shdwdrgn wrote:
BowTide wrote:from my limited calculations in the first few tanks (city driving 55 and under) 12.8-14 is best I can get, isn't that a little low for a 6 banger? Oh, it has 3.42 gears and stock 245 16's in a 'Fordstone' Destination street tire. /b]


You would have to answer a lot more questions before anyone could give you a reasonable answer. What year is your vehicle? Have many miles? How well has it been maintained (regular oil changes, etc)? When was the last time you cleaned the throttle body? Is your drive a constant stop&go, or do you do a lot of low-speed cruising? How aggressively do you drive? Do you have any extra weight in the vehicle? Towing a load? 2WD or 4WD?

As you can see, there is quite a list of things that can affect your mileage. Yes your numbers are on the low end, but if you've done something like going 50,000 miles between oil changes or strapped a sheet of plywood to your grill, then obviously your mileage would be lower than average.

[b] 75k miles, just bought it so I can't answer some of the maintenance questions, I'd say there are a moderate amount of traffic lights/stop signs and we drive fairly mildly...............HOLY SHEEP DIP BATMAN!!!! THAT'S IT, I wondered if it was that darn sheet of OSB board strapped to the grill was killing my fuel mileage! :excited: :woot:
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by KingBird » Tue Apr 15, 2014 6:38 pm

Last edited by KingBird on Sun Apr 27, 2014 1:11 am, edited 1 time in total.
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by KingBird » Tue Apr 15, 2014 9:12 pm

.
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by Shdwdrgn » Tue Apr 15, 2014 9:27 pm

Only 75k miles on a 2004? Wow that's pretty low! I also have a 2004 TB 4x4, just creeping up on 105k, and my mileage swings between 15-16.25mpg from Winter to Summer.

Definitely check into cleaning your throttle body, and take a good look at your fluid levels and what kind of condition they are in. I assume since you didn't mention it, no engine codes have popped up indicating a problem? Get yourself a couple of the larger bottles of Techron (did I spell that right?) to put in your next two tanks of gas... that will do a great job up cleaning up your fuel system and de-gunking your injectors.

And I think that's about the end of what I can suggest... anyone else want to step in?
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by BowTide » Tue Apr 15, 2014 10:50 pm

KingBird wrote:Holy crap! How'd you get a sheet of OSB to keep from breaking at 75mph?!?!?! Lol!

That's my story and I'm sticking to it, honest as a Swift driver posing as an O/O at the lunch counter at a TA.


Only 75k miles on a 2004? Wow that's pretty low! I also have a 2004 TB 4x4, just creeping up on 105k, and my mileage swings between 15-16.25mpg from Winter to Summer.
Definitely check into cleaning your throttle body, and take a good look at your fluid levels and what kind of condition they are in. I assume since you didn't mention it, no engine codes have popped up indicating a problem? Get yourself a couple of the larger bottles of Techron (did I spell that right?) to put in your next two tanks of gas... that will do a great job up cleaning up your fuel system and de-gunking your injectors.


Yea It came from WI and the dealership(?) sprayed black over the rust underneath to hide the rust so I'm thinking it wasn't used much but was exposed to deicing solutions quite a bit.
I will clean the TB for sure then.
I just returned to a right down the street beer run and noticed that the throttle is touchy from stopped/barely rolling until it shifts, maybe we need to apply the "egg under gas pedal" idea when getting up to driving speed?
The TB came from a local Chevy dealer and has a limited warranty and 2 year service agreement (I still need to read over that info!) so it has had an oil change and all fluids checked at least. I really want to change the other drivetrain fluids here soon though because I'm sure they didn't do them.
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by Shdwdrgn » Wed Apr 16, 2014 12:02 am

Mine has always been a bit like that too... touchy from a dead stop, its like it wants to launch off the line no matter how I easy into the gas. I've played with the tuning a bit to try and lighten that up, but haven't had much luck.
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by BowTide » Wed Apr 16, 2014 9:01 pm

KingBird wrote:Holy crap! How'd you get a sheet of OSB to keep from breaking at 75mph?!?!?! Lol!


:hijack:
Well let me tell ya, I used the cheaper version of 200 MPH tape to hold it on and together, I think it was called 100 MPH tape...
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by KingBird » Wed Apr 16, 2014 9:31 pm

I like this guy.
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by mikepeters1983 » Fri Apr 25, 2014 10:04 am

2004 GMC Envoy XUV, 3.73s about 151000 miles. I was getting by what the dashboard was saying 14.7 about a week ago, replaces plugs, modded cold air intake and resonator delete, now I am up to about 18.5 give or take avg. Still got to do a little more to it to see if I can improve it more.
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by nickpls » Fri Aug 22, 2014 10:17 am

Completely stock 2002 TB with 125k - 12 MPG combined city/highway. Seems a bit low, no?
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by Trail X » Fri Aug 22, 2014 10:57 am

I'd say so, unless you only drive for only like 3 miles at a time.
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by nickpls » Fri Aug 22, 2014 9:04 pm

My commute to work is about that, 3 miles. I had a few 20 mile highway trips on this tank though.

Was thinking of getting a scangauge to track mpg, anyone use one for that?

Edit: I just remembered I have a PCM4Less tune as well, forgot I got that last year.
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