To Save Money on Gas, Stop Buying Premium
Modern Engines Make Allowances for Lower Octane
The average national retail price of premium self-serve gasoline currently tops $4.018 a gallon, and may well keep climbing. Drivers who are pumping premium are undoubtedly asking themselves if they can safely switch to regular grade, which is about 20 cents a gallon cheaper. In many cases, the answer is yes.
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 knocking. Its performance will suffer only slightly: Perhaps it might be a half-second slower from zero to 60 mph. The key for drivers is to know whether premium gasoline is merely recommended or if it's required.
Edmunds has compiled two lists: "premium recommended" and "premium required" for vehicles from the 2008-2012 model years (with a few 2013 model-year vehicles). If your vehicle is on the "premium recommended" list, you're OK to switch to regular unleaded gasoline. If, on the other hand, your car is on the "premium required" list, then you should run premium fuel. You can confirm our information by checking your owner's manual — always a good idea.
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.
In the bad old days, engines could not adjust to fuels with varying octane ratings. Use the wrong fuel and the engine would knock audibly as the fuel combustion became uncontrolled. Knock is an engine phenomenon that can damage internal engine components over time.
Today, engine control systems can compensate for low octane by monitoring knock activity and adjusting ignition advance to quell the knock. 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 where lots of throttle might be used. More ignition advance allows the engine to make more power, and accelerate faster, 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.
The performance loss, however, is something you will only notice if you have a heavy foot and accelerate rapidly both from a dead stop and while changing lanes at highway speeds. But if you accelerate moderately, the loss of power is less noticeable, regardless of whether you use premium or regular-grade fuel.
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. Edmunds director of vehicle testing, Dan Edmunds, documented the performance of regular vs. premium for fuel economy in our Long Term Road Test Blog. One factor affecting the outcome of the experiment might have been that the testing was conducted in extreme hot-weather conditions.
If you want to see if you can save money by using premium in a car that doesn't require it, conduct your own test project. Fill up on regular gasoline. Record the trip mileage, gallons used, fuel price and octane rating in a notebook or in an app such as Road Trip or on site such as Fuelly. If your car has an onboard fuel economy meter, make sure you reset it when filling up. Then switch to premium fuel, do the same number of fill-ups and check the result.
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 long term engine's health. 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.