Put Premium in Wife's 2013 Malibu

My wife got a new 2013 Malibu a few months ago and I was driving it a lot this week. I forgot that it takes E85 and I, by habit, just filled up with premium fuel. I have not revealed the mistake to her, however I’m wondering what damage I may have caused and if I need to take it to the dealer tomorrow.

I’ve driven about 20 miles on this almost full tank of premium. . .

The damage is about 20 cents times the number of gallons you put in…

Your wife’s car is able to run on E85 but does not require it. There are sensors in the fuel system to constantly measure the composition of the fuel (anywhere from 10% to 85% ethanol) and the car will make adjustments to the engine management system accordingly. Drive on without worry and enjoy the better fuel economy this tank.

That’s called a “flexfuel” vehicle if you look at the plate on the back. It can use gasoline or E85. The engine management system adjusts accordingly.

Premium fuel will cause no harm whatsoever, but is a waste of money if your vehicle does not require it.

As a side note, your car will likely get the best mileage with the lowest octane gas (not E85 though) you can get away with putting in it–it probably takes 87 octane but check the manual. Usually you will get slightly less MPG out of higher octane fuel, and you will get the worst mileage out of E85, possibly offsetting any savings in price.

If you have been filling it with E85 all along, you will probably be surprised at how good your gas mileage is on this tankful of “real” gasoline.

@threephi, if you want to get the most for your money when buying fuel, buy regular gasoline with low or no ethanol. E10 is typically added to 87 octane regular, but many areas allow other octane enhancers. E85 is inefficient and will give you significantly lower fuel mileage than E10 or gasoline with MTBE. Other octane enhancers might be substituted for ethanol or MTBE. The lower the ethanol content, the better the gas mileage.

It doesn’t require E85, but it can run on it without problem

Per section 9-40 of your owners manual

“Recommended Fuel
Use regular unleaded gasoline with
a posted octane rating of 87 or
higher. If the octane rating is less
than 87, an audible knocking noise,
commonly referred to as spark
knock, might be heard when driving.
If this occurs, use a gasoline rated
at 87 octane or higher as soon as
possible. If heavy knocking is heard
when using gasoline rated at
87 octane or higher, the engine
needs service.”

You aren’t hurting anything by using premium other than your wallet though.

Since E85 is not universally available, selling a car that only runs on E85 would be both stupid and illegal. Agree with others that this is a “Flex Fuel” car and runs just as well on pure high grade gasoline than on E85.

You have to calculate how much it costs per mile to fuel it with the two different fuels. E85 will get 15% less miles per gallon, wiping out most of the cost advantage.

This may be a bad basis for comparison, but I have a '00 Caravan that is flexfuel. It actually says in the owner’s manual that if you go to from regular gas (or E10) to E85 or back that it’s best to do it somewhat gradually - i.e. you would start by putting half or quarter tank of E85 on top of an E10 before just going from empty to full on the different kind of fuel. As has been noted above, the two fuels do require different air/fuel mixes, but the computer adjusts. Not completely bombing the gas tank with the different fuel presumably makes the “adjustment” period smoother. In essence, if it has been running on E85 and you filled a near empty tank with E10 you’ll be running rich for a while. But neither you nor your wife is likely to ever notice.

You did NOT make any mistake.
as others have noted ; the E85 designation simply means that her car MAY use e85 fuel.
as opposed to vehicles like mine which can NOT ever use e85 fuel.
A ‘‘mistake’’ would be putting e85 in MY cars !

Out of curiosity, what car do you drive? I’m wondering if you’re using premium unnecessarily with that one.

I drive a 99 Mercedes E320. Everything’s fine with my wife’s car by the way.

Think about the E85 - it’s more like a 30% loss in fuel economy compared to regular, just a lot less BTUs per gallon.


That 1999 E320 definitely requires premium fuel, so you did no harm by putting premium in both of the cars

FWIW . . . and this is coming from a former Benz mechanic . . . the 112 engine in your car was one of their better designs. Quite reliable and not that difficult to work on. And it’s really able to rack up some miles. I’m sure you know all this by now

Sneak a peak at your wife’s owner’s manual. It’ll tell you everything you need to know and it’ll relieve your fears.

Sneak a peak at your wife’s owner’s manual. It’ll tell you everything you need to know and it’ll relieve your fears.

Dang! None of my wives came with an owner’s manual!

Well, not to get off topic db4690 but I do know the car can get up there on mileage. My wife got the Impala to replace her '99 ML320. She really liked her sister’s Impala and wanted to get one and she’s right cause she’s my wife and she loves it.

I’m looking into getting a new car for myself. My E320 is having some serious problems with the transmission. It’s sorta a shame to replace it after so long, but things are suddenly going wrong fast. What is the new Mercedes E-Class like?

Good looking’ but not being a Mercedes fan I don’t feel qualified to answer. If you like that brand, and they ARE gorgeous, the E class is well written about by the car mags. Top Gear, Car, Octane, and some of the other mags do good comparisons of these types of cars. Perhaps a trip to the bookstore is in order.


In regards to the '99ML320 . . . the engine and transmission were generally fine, but the vehicle itself was considered pretty atrocious. At the time, it was considered to be pretty low quality for a Benz. To put it bluntly, those early ML320s and ML430s were straight out money makers for the dealership mechanics

I take it your E320 has some serious mileage by now . . . as such, it’s probably time for a transmission rebuild. As with any aging car, there comes a time when the repairs become more frequent.

I don’t have an opinion of the current E-Class, because I left the dealership 5 years ago to become a civil service auto mechanic

@db4690 There was a lot of stuff that broke on that ML320. Lots of accessories broke and the brakes suddenly malfunctioned during a trip last summer. We don’t need to cargo room anymore so we decided to get rid of it.