Over the last month I've seen a severe drop in the MINI (just over 20MPG normally 28-30) and in my car going from 27MPG to 17.

Called the MINI/BMW shop and they said its the fourth call about R56's this month about plummeting gas mileage.

Anyone else experiencing this?

 

Winter gas formulations can affect mpg, but I don't think a 30% decrease is just due to the gas.

Any other symptoms? (running rough, hard to start, etc.)
How many miles on the car?
Where are you located?
Have you checked for any codes?

 

With shops it is either never heard of it or everyone is calling. Instead of trying to solve your issue.

Have you switched up on gas suppliers?

I lost a set of injectors years ago due to bad gas, expensive lesson. And also had some bad starting issues as well as a breakdown from water in the gas. I always seek out name brand stations with high volumes.

Also want to check the O2 sensors - will most certainly eat up the gas if they are going bad, even if they haven't failed.

 

Check the minimum octane recommended on the little sticker inside the fuel tank cap and never use anything less. Also, only pump fuel from these fine companies.
https://www.toptiergas.com/
One of the 1st things to die from NOT using Top Tier is the O sensor, another voice of experience.

 

Sorry for the late reply. Since its affecting both cars the same way, that's why I got spooked. The other car is NOT a MINI.

On the MINI. Its a 2013 with 18K miles. Runs fine, just had the oil and battery changed and thoroughly checked (got it in June). No running issues at all. Starts immediately.

Always use Premium from Chevron. Never any less octane. Same with the other car.

 

Maybe you can try using some octane booster. When I have it in my Mini, I notice a slight bump in MPG.

 

Sounds like the tanker topped off the gas station with E85. Takes 30 to 33% more fuel to make the same HP compared to gas.

 

Download the puregas app; find a station near you, and fill the car up with ethanol free fuel to see what happens to you MPG. Octane booster is great, but it can't make up for the lower energy density of ethanol. I've heard there is a government push to increase the amount (above 10%) of ethanol in our gas. This is bound to cause problems for fuel systems and engines since ethanol absorbs water in the air around it, so let your congressman know you don't want more ethanol in your gas!

The energy density of ethanol is 60% of gasoline (26.8 MJ/kg for ethanol compared to 44.4 MJ/kg for gasoline).

https://www.fuelexpert.co.za/dooctaneboosterswork.php