Fuel Mileage

pokeypokey06

Original poster
Member
Dec 24, 2011
8
I have a 05 tb short wheel base. I filled the tank and drove around 87 miles and I'm just under half of a tank. Does this seem right? Any input would help.
 

Sparky

Member
Dec 4, 2011
12,927
Fill the tank
Drive for a while down to 1/4 tank
Fill tank
Divide miles driven by gallons you put in the tank to get mpg

This will let us know if your gauge is lying or not.
 

djthumper

Administrator
Nov 20, 2011
14,955
North Las Vegas
:iagree: with both of the previous statements. Also are there any odd noises or other changes lately?
 

vipergg

Member
Dec 7, 2011
191
Assuming the guage is right then no that's not right. Even in the winter you should 300 plus miles on a tank . And it will go down even faster once you get below that half mark , at least mine does.
 

pokeypokey06

Original poster
Member
Dec 24, 2011
8
it has about 63,000 miles, no codes and 3.42 ratio. I changed oil,cleaned tb,changed plugs, front and rear diff fluid, transfer case fluid, in the past month. No strange noises or anything like that. My driving habits are mellow. It don't think it is the gauge because I installed all new stepper motors, and also a new sending unit.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
tiphat.gif
Welcome
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In case you haven't heard:
http://gmtnation.com/f5/welcome-gmtnation-com-heres-story-226/

Is it possible someone siphoned some gas out?
Until you refill and get the MPG's calculated, it's hard to tell how accurate the gauge is. :twocents:
 

Sparky

Member
Dec 4, 2011
12,927
vipergg said:
Assuming the guage is right then no that's not right. Even in the winter you should 300 plus miles on a tank . And it will go down even faster once you get below that half mark , at least mine does.

FWIW my 1st half seems to go a little faster than the 2nd half. I know, backwards of most vehicles (including my previous ones) but... :shrug:
 

jham

Member
Nov 20, 2011
1,334
What's your temp gauge readings my 2005 with 67000 miles needed the water pump replaced and t stat was stuck open and they are know to cause bad fuel mileage in our platforms
 

pokeypokey06

Original poster
Member
Dec 24, 2011
8
thermostat was just changed to. Forgot to list that one. It reads 210. As for the water pump, how do I know if it needs to be replaced?
 

jham

Member
Nov 20, 2011
1,334
pokeypokey06 said:
thermostat was just changed to. Forgot to list that one. It reads 210. As for the water pump, how do I know if it needs to be replaced?

mine started making a little noise and my heat didn't work as good as it used to
 

Iahawkeye

Member
Jan 24, 2012
52
Sparky said:
Fill the tank
Drive for a while down to 1/4 tank
Fill tank
Divide miles driven by gallons you put in the tank to get mpg

This will let us know if your gauge is lying or not.

I really think that this method is your best option. Cold hard math doesn't lie.

I always have to chuckle when someone posts how many miles they can go on a tank of gas. For starters, some of us have bigger tanks than others.:thumbsup: Another issue is what do you call a tank? Do you fill when it is an1/8? When the light comes on? Anyways, just my 2 cents.
 

Mooseman

Moderator
Dec 4, 2011
25,472
Ottawa, ON
Because of the way these gas tanks are shaped, the first 1/4 goes down fast. Then from 3/4 to 1/4 it's a slower pace. Then it goes down fast again for that last 1/4 for whatever reason (well mine does). As mentioned, actual calculated mileage is the best way to go.
 

TsBlazer

Member
Dec 13, 2011
3
pokeypokey06 said:
it has about 63,000 miles, no codes and 3.42 ratio. I changed oil,cleaned tb,changed plugs, front and rear diff fluid, transfer case fluid, in the past month. No strange noises or anything like that. My driving habits are mellow. It don't think it is the gauge because I installed all new stepper motors, and also a new sending unit.


Heh, I'm having the same problem with mine.. 72k miles and I'm averaging 11 ~ 12 mpg for a couple of tanks now.
Its empty, all fluids changed within the last 6 months, recently put a can of SeaFoam in the tank, PCMForless tune, clean air filter, clean TB. The sending unit needs to be replaced, but that shouldnt decrease mileage. (Local stealers are telling me $250 to replace it.... after the 50% off) :eek:

One thing I can think of (besides winter blend gas) is maybe a partially gooped up catalytic converter from a bad thermo. Another possibility (at least on mine), is that I have a very short drive to work, about 4 miles down a hilly road. Im thinking with that short of a drive it doesnt have enough time to get to optimal temp, possibly burning more gas...

Getting 240 ish miles per tank just sucks.....
 

vipergg

Member
Dec 7, 2011
191
TsBlazer said:
Heh, I'm having the same problem with mine.. 72k miles and I'm averaging 11 ~ 12 mpg for a couple of tanks now.
Its empty, all fluids changed within the last 6 months, recently put a can of SeaFoam in the tank, PCMForless tune, clean air filter, clean TB. The sending unit needs to be replaced, but that shouldnt decrease mileage. (Local stealers are telling me $250 to replace it.... after the 50% off) :eek:

One thing I can think of (besides winter blend gas) is maybe a partially gooped up catalytic converter from a bad thermo. Another possibility (at least on mine), is that I have a very short drive to work, about 4 miles down a hilly road. Im thinking with that short of a drive it doesnt have enough time to get to optimal temp, possibly burning more gas...

Getting 240 ish miles per tank just sucks.....

Oh yeah only driving 4 miles will do it in the middle of winter...
 

fishguy1123

Member
Dec 5, 2011
310
Finally did the math on mine today. 18.2 mpg whith a mix of hwy/city/rural driveing. I actually drove it a lil harder just to see how it would do. Probly 2/3 hwy and 1/3 mixed. DIC showed 21.2 but that was reset about a week prior so it had some carryover mileage on it as well.
 

moneypit

Member
Dec 7, 2011
214
wow, I think 18mpg is great on these buggies! I don't think we ever got that good with my daughter's driving habits...:frown:
 

fishguy1123

Member
Dec 5, 2011
310
moneypit said:
wow, I think 18mpg is great on these buggies! I don't think we ever got that good with my daughter's driving habits...:frown:

Haha... Well, that was your problem right there! :rotfl: I think if I was on a trip (hwy) it would probly be 1-2mpg better. I figure it's not bad considering it has just shy of 150,000 mi on it.
 

pokeypokey06

Original poster
Member
Dec 24, 2011
8
well I did the math. I drove it down to 1/4 of a tank. Came out to 194 miles and I put in 14 gallons. So it came out to about 13.8 mpg. So does that seem about right?
 

Blckshdw

Moderator
Nov 20, 2011
10,691
Tampa Bay Area, FL
pokeypokey06 said:
well I did the math. I drove it down to 1/4 of a tank. Came out to 194 miles and I put in 14 gallons. So it came out to about 13.8 mpg. So does that seem about right?

Pretty close, if it was all city driving. This is from FuelEconomy.gov
 

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djthumper

Administrator
Nov 20, 2011
14,955
North Las Vegas
Pretty close, it depends what all you have done to the vehicle or what mods have been done. If you haven't already give the TB a good cleaning.
 

Sparky

Member
Dec 4, 2011
12,927
pokeypokey06 said:
well I did the math. I drove it down to 1/4 of a tank. Came out to 194 miles and I put in 14 gallons. So it came out to about 13.8 mpg. So does that seem about right?

All city, highway, or 50/50 mix?
 

revamp

Member
Dec 22, 2011
223
Mansfield, TX
This is an interesting thread for me. In the past few weeks, I started smelling a light gas smell randomly, and when I am stopped it smells like my engine is drinking oil. My MPG has dropped about 2MPG. In addition, After a long commute home, after I park and have to start back up a few minutes later, it doesn't start. I have to hold to gas pedal down slightly to get it to start up.

Forgive me if this is a hijack, but I am really trying to find where these combinations exist. I just posted on another thread about possibly needing an engine rebuild in a year... I need a compression test - maybe that will reveal a lot for me.

Thoughts.?
 

Shdwdrgn

Member
Dec 4, 2011
568
Before getting my PCM tune, my city mileage stayed right around 13.8-13.9. After the tune, I was in the low 14's, but then started doing more highway driving and couldn't get an accurate apple-to-apples comparison. Last year it wasn't unusual to be seeing around 21mpg when I was on the interstate, however some time around this Fall, it dropped drastically and I can no longer seem to get above 15.2. I need to check for codes, and I know the most common cause has been the front oxygen sensor, so I'll have to see if I can get this fixed and get my mileage back.

With that in mind, I got some definite proof of an idea I've had for awhile now. I run 3.42 gears, and it just feels like much of the time it struggles once it gets into overdrive (which happens frequently even in town). This morning as I was driving down the highway at 60mph, we had some extreme cross-winds, and I was watching the average on the DIC steadily dropping. I decided to drop into 3rd gear, and even at that speed, my mileage instantly started to climb again. Even after I reached town, it continued to come up while driving in traffic, and it was certainly more responsive since it didn't have to keep dropping in and out of overdrive. Recently I've been spending more time in 3rd while driving in town, but I had no idea it would actually improve my driving on the highway as well. I'm starting to think that I should stay in 3rd any time I am running 55 or less, and reserve 4th for the interstate.
 

jbones

Member
Dec 5, 2011
658
Shdwdrgn said:
I run 3.42 gears, and it just feels like much of the time it struggles once it gets into overdrive (which happens frequently even in town).

I don't know if this falls into play for your circumstances, but, your tire size 30-31, and gear ratio 3.42; Good Fuel Economy but less power, good for flat highway driving

Differential Gear Ratio Chart - Tire Size to Gear Ratio

Someone posted a chart on another thread, don't remember is this is the same chart.
 

Sparky

Member
Dec 4, 2011
12,927
Interesting. According to that chart, the guys who have a 3.73 ratio with a lift/bigger tires would probably do better on the highway than the rest of us with a 3.42 ratio and the same tires.

Also helps solidify my theory on why I saw the mpg increase going from 3.08 to 3.42 on my Camaro I had.
 

Shdwdrgn

Member
Dec 4, 2011
568
interesting data on that chart, and it just helps confirm that for my purposes (75% city driving and occasional towing of 5000+ pounds up a mountain), switching to 3.73 gears would give me an all-around gain. More and more, I am surprised that the 3.73's did not come standard for our trucks.
 

jbones

Member
Dec 5, 2011
658
Shdwdrgn said:
More and more, I am surprised that the 3.73's did not come standard for our trucks.

Me too. I guess GM didn't figure on the truck being used for more than taking Johnny to school. The cost of new gearing dosen't even put it close to any mods for me. Even if I had the dollars its' way out of my skill range.
 

Shdwdrgn

Member
Dec 4, 2011
568
jbones said:
Me too. I guess GM didn't figure on the truck being used for more than taking Johnny to school. The cost of new gearing dosen't even put it close to any mods for me. Even if I had the dollars its' way out of my skill range.

It is unfortunate that we 4x4 owners have double the cost for such conversions. Someone told me awhile back of a place I could get the gearing for around 250-300 each. On the other hand, it might be worthwhile to check the local yards and see if I can find a set available for a better price.
 

jbones

Member
Dec 5, 2011
658
Shdwdrgn said:
It is unfortunate that we 4x4 owners have double the cost for such conversions.

That's the spoiler for me, front and rear. So far not towing anything, and only 255/65/17, so with those tires and the 3.42 it's a good ratio for me right now. Or should I say one I have to live with.
 

fishguy1123

Member
Dec 5, 2011
310
Just filled up from aprox 1/2 tank. This time most of the miles were rural/city with about 60 out of 168.7 hwy (70-75mph). DIC read 20.9 and actual was 18. My last calc was 3mpg less than DIC and so it this one.
 

Iahawkeye

Member
Jan 24, 2012
52
fishguy1123 said:
Just filled up from aprox 1/2 tank. This time most of the miles were rural/city with about 60 out of 168.7 hwy (70-75mph). DIC read 20.9 and actual was 18. My last calc was 3mpg less than DIC and so it this one.

From what i have heard, the DIC has always been a little generous. Maybe, GM wants you to feel better about your mileage... That is why I think to get a real comparision for mileage, you have to divide miles and gallons. Shoot, create a spreadsheet. I know it is a little nerdy, but I have accurate information for the last 3 years that I have owned my envoy.
Avg gas Miles Gal MPG

Yearly Miles $2.53 13358.9 885.62 15.08423477 Yearly mileage totals…15.08mpg
Yearly Miles $2.52 18022.1 1061.852 16.97232759 Yearly mileage totals…16.97mpg
Yearly Miles $2.89 19466.8 1167.987 16.66696633 Yearly mileage totals...16.67 mpg

Someone on this forum (or the old place) said that they did this and I was impressed. It is also a great place to log in your repairs and maintainance. Again, it is a little overboard, but a great resource that is handy if you are willing to put in a few minutes everytime you fill up.
 

djthumper

Administrator
Nov 20, 2011
14,955
North Las Vegas
jbones said:
I don't know if this falls into play for your circumstances, but, your tire size 30-31, and gear ratio 3.42; Good Fuel Economy but less power, good for flat highway driving

Differential Gear Ratio Chart - Tire Size to Gear Ratio

Someone posted a chart on another thread, don't remember is this is the same chart.
That is basically the same chart that I posted.

jbones said:
Me too. I guess GM didn't figure on the truck being used for more than taking Johnny to school. The cost of new gearing dosen't even put it close to any mods for me. Even if I had the dollars its' way out of my skill range.
You have think that they put them out as more of a soccer mom vehicle not for off road use like a lot of are doing with them now. I have noticed that a lot of rental car companies got the 3.42 with the 4WD so that they could offer a 4WD SUV in the mid-size range. Chief, you have fishstick in range of you to help do this.

I guess I noticed this more then everyone else because there is nothing but mountains around me where every I go. I felt it big time after I went up in size last year followed with a trip hauling stuff that I hauled the week before with the stock tires.
 

jeremym

Member
Jan 19, 2012
8
If you have an android phone there is an app called Car Maintenance and will calculate MPG as well as let you input different maintenance things to remind you when its time change the brakes/wipers/transmission fluid/etc...
 

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