When the price of gasoline spikes, drivers scramble to reduce fuel costs. A quick way to save at least 20 cents per gallon (often as much as $4 per fill-up) is to stop pumping premium gas and switch to regular grade. But how will you know if the switch is safe or if it will damage the engine in your car?
The key for drivers is to know whether premium gasoline is merely recommended or if it's required. In today's automobiles, advances in engine technology mean that even if the owner's manual recommends premium gasoline, the car will typically run on regular without issue and won't damage the engine in any other way. The car's performance might suffer only slightly: it might be a half-second slower from zero to 60 mph, for instance. But the average driver isn't likely to notice this drop-off.
Drivers used to buy a tank of premium gas every once in a while to clean their engine. Years ago, premium gasoline contained more detergents and additives to stop carbon deposits. But experts say that because of government regulations aimed at cutting emissions, all grades of gas, including those you buy at independent, low-price stations have plenty of additives to both protect engines and cut pollution.
Edmunds has compiled two lists: "premium recommended" and "premium required" for vehicles from the 2009-2014 model years (with a few 2015 model-year vehicles). If your vehicle is on the "premium recommended" list, you're OK to try switching to regular unleaded gasoline. If, on the other hand, your car is on the "premium required" list, then you have to run premium fuel. You can confirm the information on these lists by checking your owner's manual.
Smarter Engines Protect Themselves
If you're still in doubt about switching to a lower-octane fuel, here's a deeper explanation of why the change is unlikely to hurt your car.
First of all, premium gas is more expensive because it contains a higher percentage of octane. Why is this important? When vaporized gas mixes with air and fills the combustion chamber, it is compressed by the rising pistons. This makes the gas-air mixture grow hot and it could ignite before the spark plug fires, pushing backward on the piston. Higher-octane fuels can be compressed to a greater degree without self-igniting. That's why premium gas is used in high-performance engines.
In the old days, engines could not adjust to fuels with varying octane ratings. Use the wrong fuel and the engine would knock or "ping" audibly because the gas exploded prematurely. This knocking damaged internal engine components over time.
Today, engine control systems can compensate for low octane by monitoring knock activity and adjusting ignition advance to avoid knocking. This sophisticated electronic capability effectively tunes the engine on the fly and gives drivers more flexibility in the grade of fuels that they can safely use.
Compared to premium gasoline, lower-octane fuels don't allow the engine to run as much ignition advance during situations calling for rapid acceleration. More ignition advance allows the engine to make more power, and accelerate more quickly, during these conditions. Since the engine doesn't make quite as much power with lower-octane fuels, this translates into slower acceleration in cars for which premium fuel is recommended. The performance loss is especially noticeable in turbocharged gasoline engines, which have become increasingly popular in recent years.
The performance loss, however, is something you will only notice if you have a heavy foot and accelerate rapidly from a dead stop or while changing lanes at highway speeds. But if you accelerate moderately, the loss of power is barely noticeable, regardless of whether you use premium or regular-grade fuel.
When Premium Can Be a Money-Saver
Edmunds has noted, however, at least one case in which a car with a small turbocharged engine got better fuel economy when running on premium. The car in question was a 2011 Chevrolet Cruze LTZ and, perhaps befitting a car that's marketed as a money saver, the owner's manual only calls for regular unleaded gasoline. Yet in a specific test we noticed that we got better fuel economy (and ultimately saved a bit of money) by using premium fuel. One factor affecting the outcome of the experiment might have been that the testing was conducted in extreme hot-weather conditions, however.
If you want to see if you can save money by using premium gas in a car for which it's recommended but that doesn't require it, conduct your own test project. Monitor your fuel economy and performance over at least two tanks of premium gas. Record the trip mileage, gallons used, fuel price and octane rating in a notebook or in an app such as Road Trip or on a site such as Fuelly. If your car has an onboard fuel economy meter, make sure you reset it when filling up. Then, fill up on the same number of tanks of regular gasoline and record all the same data. Finally, compare the results. You're looking for a drop-off in fuel economy or a sense that the car is slower or hesitant under strong acceleration.
That's the drill for a premium-recommended car. You can stay with premium, or step down to regular unleaded if you want to.
It's a different story for a car whose engine requires premium fuel. The car will still run on regular fuel in a pinch, but you shouldn't make a habit out of it. The fuel's lower octane can result in elevated exhaust-gas temperatures and possible knocking, both of which can adversely affect the engine's health in the long run. Running regular-grade fuel in a car that requires premium might sound like a good way to shave a car's running costs, but the short-term savings won't come close to offsetting the cost of repairs to a damaged engine.
For those driving "recommended premium" cars, however, it's just a matter of driving moderately and avoiding acceleration with a wide-open throttle. Do that and you might never feel the difference between using premium and regular grade gasoline: and neither will your car.