What could be causing my car's MPG to stay 4 under the highway rating?

[NoraGH]

I’m trying to figure out if my car’s fuel economy is normal or if something’s off. I drive a 2018 sedan and my last few tanks have been consistently under the highway rating by about 4 MPG, even though my commute is mostly steady 65 mph cruising. I’ve checked the tire pressure and it’s fine, so I’m wondering what else could be causing it.

[EmmaLR]

Yep, EPA numbers are under ideal conditions. With a steady 65 mph, I saw tanks about 4 MPG below the highway rating, especially when it’s hot or windy. Small things like how smooth the cruise is or occasional drafts can tilt that a lot.

[Justin.M]

I did a quick maintenance pass and it didn’t solve the gap. Replaced the air filter, spark plugs, cleaned the MAF. Mileage ticked up a notch but not dramatic.

[Richard.L]

Have you checked live data for fuel trims or misfire codes? If the O2 sensors or a converter are drifting, you’d see worse numbers.

[Thomas_T]

Maybe the issue isn’t the numbers at all. Could be how you’re measuring, fill technique, or the car warming up in cold weather; those can make the same drive look different from tank to tank.