Anyone know why tank mileage drops down after oil change

isisleo86

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When i first got my 15 Kia my tank would show 360 miles to empty when i filled it. I got my oil changed last Janurary and it was the same. A new company took over my dealership a few months after. I got my oil changed in July and my tank mileage after was about 320 miles when I filled up. It stayed steady until my oil change last weekend. Now the display says I have 300 miles to empty when i fill up :francis:.

My mpg is roughly the same it's just my miles to empty drops after every oil change. I get my tires rotated and balanced rregularly and had my 25,000 check up. Could the dealership be fukking me over either by not changing the oil correctly or actively sabotaging me?
 

Art Norm

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If they overfill it, that can affect gas mileage. Using the wrong weight oil will cause it to drop, also. Are they just changing the oil, or did they change the air filter, too? An old, dirty air filter can drop gas mileage as well. The gauge could be off. Fill it up, set the trip odometer to 0, and see what it reads when you hit E.
 

MR. SNIFLES

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THUNDER BUDDIES
THEY RESET YOUR FUEL MILEAGE HISTORY. HAPPENS ALL THE TIME. IT HAPPENS ON OUR CARS AFTER OIL CHANGES. ONE OF MY JOBS IS TO LOG FUEL ECONOMY ON OUR FLEET. IT THIS IS THE CASE IT WILL FALL IN LINE AFTER A FEW FILL UPS.

THE COMPUTER THAT CALCULATES YOUR FUEL ECONOMY DOES SO BY CALCULATING YOUR CURRENT MPG MIXED WITH YOUR MPG HISTORY. WHEN CARS COME FROM THE FACTORY THEY HAVE WEIRD FUEL ECONOMY NUMBERS BECAUSE THEY HAVE NO HISTORY AT ALL. MOST CARS ARE SHOW AROUND 3-10 MPG UNTIL IT IS DRIVEN FOR ABOUT 50-100 MILES. AFTER THAT IT WILL SHOW CORRECTLY WHEN FILLED UP.

IF YOUR LUBE SHOP RESETS THE FUEL ECONOMY HISTORY IT WILL THROW THE NUMBERS OFF A BIT. A HARD RESET OF THIS NUMBER WILL HAVE A DRASTIC EFFECT ON THE FUEL CALCULATION. YOU USUALLY HAVE TO PUT THE CAR IN ENGINEERING MODE FOR THE 2ND OPTION.
 
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