2015 Fusion Hybrid
 

I have been averaging 53 to 55 mpg using only Mobil fuel. I just refilled at a different Mobil station and my mpg dropped to 34 mpg. Can anyone explain this? My driving is no different. I was thinking of the air conditioning cutting into the mileage, but I have used the air for the past two years and it kept the same good mileage.

See what happens on the next fill. My guess would be a fill discrepancy based on the different station, possibly the slope your car was parked on resulting in an incomplete fill on the prior tank.

If you "just refilled" as stated, your MPG reading will be very inaccurate for the first few miles, car computers are famous for stupidly high, or low estimates. Give it a chance to settle and see what happens.

Thanks. I will wait until my next fill-up
john