2. What About Diesel?

Did you know that Subaru has been making a diesel BOXER® engine for some time now? It just isn't available in the United States, so you probably don't have to worry about filling your Subaru up with diesel. In fact, the brass at Subaru has indicated that they're going to stop making the diesel engine and instead focus on making electric vehicles. So, it's you're more likely to be plugging in a new Subaru than you are to be filling up with diesel.

3. Can I Use Ethanol In My Subaru?

Ethanol is a plant-based fuel that has less chemical energy compared to gasoline -- but it does have a much higher octane rating. To help reduce dependence on the oil supply, most of the gasoline sold in the United States is about 10% ethanol and only 90% pure gasoline. 10% ethanol has been found to be safe to use in virtually all modern cars with fuel injection technology.

That said, you'll now find a variety of other ethanol blends at the pump, including E85 FlexFuel and new blends like E15 and E30. The number that follows the E tells you what percentage of that fuel is ethanol. FlexFuel is up to 85% ethanol and just 15% gasoline; E30 is 30% ethanol.

To find out what ethanol blends are safe to use in your car, just check the owner's manual. For example, the owner's manual for the 2020 Subaru Outback indicates that the standard 2.5L engine has a 10% ethanol limit -- meaning you should only use regular gas. However, 2020 Subaru Outback models with the 2.4L turbocharged engine can safely use up to 15% ethanol. That means you can fill your 2020 Subaru Outback XT with E15 fuel without any issues.

4. Why Do Some Engines Need Premium Fuel?

When you approach a fuel pump at your local filling station, you'll probably find at least three different kinds of gas. Usually, they're separated into regular, mid-grade and premium gasoline. Premium gasoline has a higher octane rating compared to regular gas. The octane rating of a particular gas tells you how much it resists early detonation, a.k.a. engine knock.

On ordinary Subaru family vehicles like the Ascent and Forester, regular gas is all you'll need. However, the engines found in the Subaru BRZ, the Subaru WRX, and the Subaru WRX STI are built for higher compression with a powerful turbocharger -- as a result, regular fuel can be problematic in these engines. Instead, premium gas is required. Premium fuel is more stable and won't combust early inside high-performance engines.

If you're the type to "treat" your regular engine to a tank of premium fuel every so often, you might keep that extra cash in your pocket. Higher octane fuels don't burn cleaner or provide more power. If your car was designed to run on regular fuel, there's really no advantage to filling up with premium fuel.