SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/cars-oil-grade-mpg

Your owner's manual says 5W-30 oil, but the shop puts in thicker 10W-30. What can happen?

Your gas mileage can drop. The recommended grade gives the best mileage.

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  1. Your gas mileage can drop ✔
  2. Mileage goes up, thicker is better
  3. Nothing, all oil grades are the same

Why: The Department of Energy says using a thicker grade than the engine was designed for can lower gas mileage. Follow the grade in the owner's manual.

Huh, didn't know that: DOE estimates that using the recommended oil grade can improve gas mileage by 1% to 2%.

The dad joke
I had a dream that I was a muffler last night. I woke up exhausted!
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References

Answer: Your gas mileage can drop. The Department of Energy says using a thicker grade than the engine was designed for can lower gas mileage. Follow the grade in the owner's manual.

  1. Keeping Your Vehicle in Shape (fueleconomy.gov, US DOE) www.fueleconomy.gov/feg/maintain.jsp
    using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage
    Checked 2026-10-11.

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