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Q: My truck uses a lot of gas

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I installed an after market muffler onto my truck. The first couple of months was fine but then I realized my truck was using too much fuel. I fill it up and about 5 days it's all gone. What's the issue ? Thank you

My car has 25000 miles.
My car has an automatic transmission.

A: Hey there. There are many versions of your ...

Hey there. There are many versions of your vehicle, so the mileage varies between 17 to 20 (combined city/highway) depending on the version. See fueleconomy.gov to determine what the rated mileage is for your version of the vehicle. The flex fuel version (using E-85) of your vehicle will have much lower mileage, reflecting the much lower energy content of the fuel. If after measuring your actual fuel economy it is 10% or more below the government published rating, then you have a problem.

Whether the degradation is due to an aftermarket muffler or not is not clear. You would have to talk to the manufacturer about their product specifications and how such compares to OEM. It is technically possible to measure back pressure in the exhaust system if the need arose. But aftermarket exhausts are required to allow the vehicle to function per government mandated fuel economy standards. If these aftermarket parts didn't, and caused a degradation in your results, that would be a problem. In your circumstance, I would first carefully measure the actual fuel economy you are getting over a period of about a month. Simply compare those data with the rated (expected) performance of the vehicle. If the values are within 10%, that is within an acceptable range due to differences in climate, elevation, driving characteristics, and variances in loads that are carried in these trucks. If you would like to get the truck's gas usage inspected by an expert, a certified professional from YourMechanic can come to your car's location to have this examined.

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