ALTOONA, Pa. (WTAJ) — Gas station chain Sheetz is once again lowering the price of gas, this time for the rest of April. But there’s a catch: The discounted price is only for one certain type of fuel.

Sheetz announced Monday that the price of E85 (flex fuel) will be dropped to $1.85 per gallon from April 17 to midnight on April 30. That’s about half of the national average for a gallon of gas, which was $3.67 on Monday according to AAA.

Sheetz has locations in Pennsylvania, West Virginia, Virginia, Maryland, Ohio and North Carolina. This price drop will be available at the chain’s 375 locations across those six states that sell E85. 

In order to benefit from the promotion, you need to first make sure your car can burn E85 gas.

E85 is approved for use in “flexible fuel vehicles,” which are designed to run on gasoline or gasoline-ethanol blends of up to 85% ethanol (E85). 

According to the Department of Energy, E85 contains between 51% and 83% ethanol, making it a cleaner-burning fuel than other fuel grades. Because of its high octane and clean burning, E85 is a popular low-cost alternative for drivers whose cars can handle it.

Not sure if you can use flex fuel? There’s an online tool you can use to find out. Just click here to enter your vehicle’s manufacturer and find out.

If it accepts E85, your car might also have a yellow gas cap or a badge that advertises it as a “flex fuel” vehicle. The owner’s manual for your car should also specify what types of gasoline it can tolerate.

The Department of Energy says flexible fuel vehicles — or flex-fuel vehicles — have been manufactured since the ’90s, and these cars “experience no loss in performance when operating on E85, and some generate more torque and horsepower than when operating on gasoline.”

However, because ethanol produces less energy than the same volume of standard gasoline, flex-fuel vehicles will get fewer miles to the gallon when using E85.

Sheetz reminds drivers that E85 is clearly designated as a different fuel type, and should not be used in standard vehicles.

If you do put E85 in a car that isn’t meant to run on flex fuel, your Check Engine light will probably come on, according to Progressive. A one-time mistake might not be a huge deal, but doing it repeatedly could cause serious corrosion, the insurer warns.

“Plus, when you accidentally put E85 fuel in a car, it may void your engine warranty,” Progressive explains. “That means you could be on the hook for the repairs, even if your car is brand new.”