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Increase My Fuel Economy


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  • 3 weeks later...
Just wondering what I can do to my engine to increase my fuel economy. I already have a Flowmaster dual exhaust on the truck. I'm running 265/75/16 tires, so I know that isn't helping, but it came with them on. Any suggestions are appreciated.

 

Sorry I can't offer anything, but I heard putting the 265/75 on vs. 245 actually increases mileage because of the gear ratio change, you should be running lower rpms. But then they are heavier so I don't know....

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Your flowmaster is hurting you. :P

 

I lost mileage when I added the flowmaster to my 2003 5.3. Lost low end torque which had a bad effect on mileage intown. Only thing I can suggest is a custom tuned "geared" for mileage instead of power. What gears does your truck have? 245's would help too. But imo, not worth the change.

 

Just about anything you do other than a tune will cost alot more than the savings you'd get.

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Your flowmaster is hurting you. :P

 

I lost mileage when I added the flowmaster to my 2003 5.3. Lost low end torque which had a bad effect on mileage intown. Only thing I can suggest is a custom tuned "geared" for mileage instead of power. What gears does your truck have? 245's would help too. But imo, not worth the change.

 

Just about anything you do other than a tune will cost alot more than the savings you'd get.

 

 

I second the custom tune. I used to have a 4.8 in a 01 silverado Z71. The only thing I had done to it was a magnaflow muffler, K&N intake and the custom tune and I got between 18 to 19.

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Your flowmaster is hurting you. :P

 

I lost mileage when I added the flowmaster to my 2003 5.3. Lost low end torque which had a bad effect on mileage intown. Only thing I can suggest is a custom tuned "geared" for mileage instead of power. What gears does your truck have? 245's would help too. But imo, not worth the change.

 

Just about anything you do other than a tune will cost alot more than the savings you'd get.

 

 

I second the custom tune. I used to have a 4.8 in a 01 silverado Z71. The only thing I had done to it was a magnaflow muffler, K&N intake and the custom tune and I got between 18 to 19.

 

 

Flowmaster to magnaflow is a big difference for the better.

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  • 3 weeks later...

What kind of fuel mileage do you get with your 4.8? I'm getting only 5 km/L which is about 12.5 miles per gallon

 

The truck has just under 200,000 km's (so about 125,000 miles) and it is all stock with the exception of 265/75/16 tires

 

Anything I should check that could be causing my truck to waste more gas?

 

Also, truck has an auto transmission

 

The factory build sheet says I should be getting 18 mpg city and 24 mpg highway but I'm getting half of that

Edited by 2001gmcsierra
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Are you talking US gallons or Canadian/Imperial gallons? Also, is your tire size larger than stock. If so have you had the speedo recailbrated?

 

Plugs, wires, if they haven't been done already. Air filter?

 

Did you buy this truck new or used?

 

 

 

 

Edit: change gallon term

Edited by txab
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Are you talking US gallons or Imperial gallons? Also, is your tire size larger than stock. If so have you had the speedo recailbrated?

 

Plugs, wires, if they haven't been done already. Air filter?

 

Did you buy this truck new or used?

 

 

I'm using 3.78L = 1 gallon

 

Yes the tires on it (265/75/16) is a bit bigger than stock (245/75/16)

 

No, I haven't had anything done to the speedo

 

I just bought this truck used and the gas mileage is killing me

 

I haven't changed any of those items that you listed, so do you think if I change them it will increase the gas mileage or is my truck getting average mpg?

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You're not getting an accurate reading on distance traveled. Which throws your calculations off. You should be doing a bit better than you are on MPG. Do you know what your rear gear ratio is? There is an RPO code listed in the glove box door. Should start with "GT".

 

Are you toting around a bunch of weight in your truck?

 

Mileage wise your truck is due for plugs/wires, if they haven't already been replaced. It's something to look into. Do you know the maintenance history of this truck? I'd get an accurate measurement of my distance I traveled then figure fuel mileage.

Edited by txab
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You're not getting an accurate reading on distance traveled. Which throws your calculations off. You should be doing a bit better than you are on MPG. Do you know what your rear gear ratio is? There is an RPO code listed in the glove box door. Should start with "GT".

 

Are you toting around a bunch of weight in your truck?

 

Mileage wise your truck is due for plugs/wires, if they haven't already been replaced. It's something to look into. Do you know the maintenance history of this truck? I'd get an accurate measurement of my distance I traveled then figure fuel mileage.

 

First I just want to say thanks for helping

 

Do you think it makes a really big difference in my actual MPG than what I am calculating according to the trip meter...like how big of a difference do you think the tires make? They are only about 1.5" bigger than the stock tires.

 

No, the truck isn't hauling anything but it does have a canopy but I don't think that's very heavy

 

Truck was meticulously maintained by original owner before I bought it...I'm gonna check the air filter tomorrow and I will change the plugs/wires soon as well....will these increase the fuel economy?

 

Would it be unrealistic of me to ever expect to get around 17-18 mpg out of it? If I can't get somewhere near there than I might have to sell it

 

Also, I will get you the gear ratio tomorrow

 

Thanks again

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With your tire size difference, your speedo is off 2.3 mph (3.9%). At 60 mph you're actually running 62.3 mph. (100 kph vs 103.9 kph) You are covering more ground than your odometer is showing. Any way you can talk with the previous owner and see what kind of mileage he was honestly getting? Also find out when he serviced the plugs/wires. Don't spend money if you don't need to. Air filter is a inexpensive changeout.

 

The reason I asked about the rear ratio, many times the 4.8 comes with a ratio number less than a 3.73. To get better towing/driving performance many people will swap to a 3.73 or 4.10. If your truck came from factory with 3.08 or 3.23 that's what the mileage estimate you have on the sticker is based on. So if ratio has changed so will mileage.

 

As Steven stated previously in this thread a custom tune would probably do you a world of good. Also you do have a truck with 125k on the clock. So its efficiency has dropped some through wear and tear.

 

Are you running a quality 5w-30oil? Are you buying a good brand of fuel? Cheap gas can lower mileage. Fuel blend makes a difference as well. Winter blends and ethanol blends can affect a difference on mpg.

 

Have you scanned your truck for codes set in the computer? Your O2 sensors may be allowing you to run a bit rich. As they age they can get lazy and not perform at their best. They can still be within range so no codes will be set. What about your engine temperature? Does the truck warm up as it should or does it take a while? You should have a 186 degree thermostat. If a stat is stuck open or has been changed to a lower temp, your truck may burn more fuel, unless a tune has been done on it to compensate for the temp difference.

 

Depending on the configuration and construction of your topper, you may be hauling a bit of weight. What are your driving conditions? Flat, level or a hilly conditions?

 

Here's something I found:

 

To the person who said MPG goes down with larger tires. That may be, but it has nothing to do with your answer, which said larger tires are heavier, and more to do with how the car is driven and engine power curves. A larger tire size is going to add at best a few ounces to the weight of the tire. In fact, the lead balancing weights might make more of a difference in tire weight. A few ounces on a 3,000 car makes no difference. The power to start a vehicle from a dead start would be affected by tire size, but not due to tire weight. This whole concept is demonstrated by the fact that vehicles need a transmission. (If the car just had one gear, 4th, the engine would not have enough power to start the car from a dead stop. That's why there is a transmission.) A larger tire would make a vehicle a bit harder to get moving. But, the trade off means the vehicle would take less energy to keep it moving with larger tires. Therefore, if a car is used primarily for highway driving, overall MPG may improve with larger tires. For city driving, with lots of starts from dead stops, MPG may get worse with a larger tire. This has a lot to do with transmission design, where vehicle manufacturers gear the cars for a good blend of city/highway fuel economy, also based upon the power sweet spot of the engine (and tire size!). However, for cars used for a lot of highway driving, significantly better MPG may be achieved by gearing the transmission to use lower engine rpm's at highway speeds. (Especially with diesels). But regearing, if even possible, costs a lot of money. Increasing tire size is a cheap way of doing the same thing. A bigger tire will go farther distance during one revolution, meaning you need less engine rpm's to turn it.

 

As for the original question, tire size is DIRECTLY related to speed and mileage readings on your speedometer/odometer. Your speedometer expects the car to go a certain distance for each revolution of the tire. Imagine: If the tire is HUGE, the car will go very far with one revolution. (Your speedometer readings will change with new tires vs old!) Almost every vehicle in the country is purposely made to READ about 5 mph HIGHER THAN actual speed. I say the manufacturers do this to make the vehicle odometer rack up the miles more quickly, which is "Gotcha Capitalism" at work. But, the manufacturers avoid massive class-action lawsuits by claiming they must do this to make absolutely sure that the car isn't going FASTER than speedometer speed so they don't get sued by people who get a ticket.

 

From a purely geometric perspective, changing the tire diameter could effect the "Perceived Mileage" - assuming the odometer (and speedometer) tabulates the revolutions (RPMs for the speedometer), the traveled distance would be greater than the measured distance if the tire size was increased. (Just as someone would run slightly further if they ran around a track in lane two versus lane one.) Calculating the MPG would provide an error unless the odometer/speedometer was recalibrated for the different size of tire.

 

A friend of mine was once pulled over for exceeding the speed limit shortly after putting larger tires on his vehicle. His speedometer measured his speed right at the speed limit, but his actual speed was higher.

 

This error does not "change your mileage", rather just gives an erroneous value if you are using your odometer. If you are using known distances in your calculation instead of your odometer, you would avoid this problem.

 

However, newer/luxury cars may be using GPS or other high-tech detection methods to determine distance and speed, rather than tracking the revolutions of the axle - thus eliminating the error and the need to recalibrate.

 

From a mechanical perspective, an increase of tire/rim diameter might effect the efficiency of the transfer of energy or torque upon the axle. However, I would speculate that the change would be negligible.

 

In summary, I would suspect that the change in tire size would have minimal effect on your "actual mileage", but the "measured mileage" could easily vary as a result of calibration issues.

 

Also here's a short video:

 

http://www.ehow.com/video_4997503_bigger-s...as-mileage.html

Edited by txab
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I've got a 5.3 and I get 15 city, about 19 highway. 76k on the odometer. I'd think you should be doing better than you are. You need to find out answer to some of the other things I pointed out. Could the rear gears have been changed put because the previous owner needed to tow larger loads

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Rear gears are stock, I will check which gears are in it this evening

 

A mechanic told me I should get o2 sensor extenders installed in the front 2 o2 sensors, and he said this will increase the fuel mileage by about 13 mpg on the highway and about 8 mpg in city so I could be looking at about at least 20 mpg city and about 25 mpg highway and it costs $140 for the pair of o2 sensor extenders

 

I researched the o2 sensor extenders a bit but I couldn't find if they damage the engine in any way or cause a loss of power....all I learned is that they cause less oxygen to be detected by the sensor so less fuel is consumed

 

Has anyone had o2 sensors installed and can you share the results?

 

Here is a video:

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