Auto Repair Encyclopedia
Regular Gas: Is It Okay to Use in Your Car?
It's happening to most of us. As gas prices rise, we look for ways to save money on what's beginning to feel like liquid gold. Some options include carpooling, taking public transit, working from home, and cheating at the gas pump. Sure, your car's owners manual says to use premium fuel, but filling an empty tank with premium can cost as much as $6 more than a tankful of regular. Do you take the chance on cheaper fuel? Can using regular gas when your car calls for premium harm the engine? Depending on what type of vehicle you have, yes, it can.
The Differences
Premium gasoline has a higher Octane Number Requirement (ONR) rating than regular. ONR is a measure of gasoline's ability to resist pre-igniting, or knocking, when burned in an engine. Because premium fuel has a higher ignition resistance, it's recommended for high-performance and luxury engines with turbochargers, superchargers, and higher compression ratios—in other words, engines that produce more pressure and heat. Because premium gas resists ignition longer than regular, premium causes consistent burning in these engines, which produces optimal fuel economy and performance. However, spending more on gasoline with a higher ONR than recommended in an unmodified engine is a waste of money.
The Potential Harm
When gasoline with an ONR lower than recommended is used in a vehicle, the pressure and heat produced by the engine ignite the fuel rapidly and unevenly. This is what causes the dreaded pinging or knocking noise most often heard under heavy acceleration or load. Do these noises indicate harm to your engine? If it happens only occasionally, it isn't serious, but frequent knocking can cause
Newer cars have a sensor that detects knocking. The sensor makes preventive adjustments when you use lower-ONR gasoline. But these adjustments come at the cost of power and acceleration.
In the long run, if you use regular gas when your owners manual calls for premium, harmful engine deposits will accumulate. This can not only increase the likelihood of knocking but also can increase emissions while reducing fuel economy.
In sports cars with turbo- and superchargers, using a lower-than-recommended-ONR gasoline is an especially dangerous proposition, particularly if the vehicle is driven hard and sees excessive boost pressure. The potential damage can be catastrophic and expensive.
In Summary
Although it's possible to use lower grade gas than recommended, the money you save now will disappear the moment your car has to go into the shop for engine repair or replacement. If you occasionally need to use lower grade gasoline because premium isn't available, don't fret, but don't make it a habit. If you want to keep your car running strong and well for many years to come, always follow directions in your owners manual, and fill up with the recommended grade of gasoline.
