High-Octane Gasoline May Not Be the Best Solution

Times Staff Writer

Question: Is there any advantage to using higher-octane gasoline, such as premium instead of regular, either as a steady diet for a car’s engine or intermittently?--H.A.O.

Answer: It is a time-honored tradition for many motorists to burn an occasional tank of premium as a substitute for regular, in the apparent belief that it may do some good for their engine. In all likelihood, it does almost nothing beneficial.

All gasoline has an octane rating, which is a measure of the resistance of the fuel to uncontrolled combustion inside the engine. Uneven or uncontrolled combustion typically causes engine ping, which may or may not cause engine damage, depending on its severity.


Every engine has an “octane rating,” meaning that its basic design requires gasoline that has a certain octane. The octane rating is contained in the owner’s manual and is sometimes posted near the gas-tank cap.

Necessary Protection

If an engine is rated for regular, which is typically 87 octane in unleaded gas, then that fuel should provide all the necessary protection for the engine.

Higher-octane fuel does not burn hotter. It will not clean out deposits from an engine combustion chamber. And it will not provide any higher fuel economy.

But an engine’s octane rating can change over time. That is because as an engine ages, it can accumulate deposits inside the combustion chamber. These deposits effectively reduce the volume of the cylinder and thereby raise the combustion ratio of the engine.

As a result, it is common to find that engines ping as they get older, even though they never pinged when they were new. If the ping becomes regular and particularly heavy, it may be necessary to buy a higher-octane fuel to control the ping. In some cases, ping can seriously damage an engine. You should check your owner’s manual for advice or consult a dealer to see how much ping is acceptable for your car.

Some Advantages

Be aware, though, that premium fuel may offer some advantages in the area of additives. Every gasoline refiner puts in a very small quantity of additives, amounting to between two-tenths of 1% and four-tenths of 1% of the volume of the fuel.

These additives help stabilize the fuel and inhibit rust in the fuel system. They also contain a detergent to help keep fuel system parts clean, which is especially important in fuel-injected engines. Some additives help control engine deposits.

It is commonly believed that premium fuels contain a better additive package. This is not always the case. Many name-brand refiners put the same additive package into their regular and premium fuels.

Check Advertising

Of course, gasoline companies would never make it so easy on motorists as to actually disclose whether their premium fuel contains the same package as their regular. You may, however, be able to guess by the company’s advertising. If a company pushes its premium fuel as a product that offers improved engine protection, then you could surmise that it has increased the dose of additives in that product.

Unfortunately, that leaves a lot to the imagination, both your own and the company’s.

Another big unknown in gasoline is where refiners get these additives. About one-half of U.S. refiners simply buy their additives from vendors who offer the same packages to many companies. A few refiners actually concoct their own additives. Again, it is difficult, if not impossible, to know which companies make their own additives and to know whether these are any better than the off-the-shelf products.

Gasoline is a “blind product” for most consumers. Unlike motor oils or car tires, gasoline is largely unrated and sold with few disclosures to the consumer. In many cases, the brand-name fuel you are buying was not even refined by the company whose name is on the pump. And the crudes used to refine gasoline have different properties. In some cases, high-sulfur crudes create obnoxious odors. The disclosure requirements should be better.

Q: I have a 1985 Camry with a baffling problem. After I drive about 4 miles, the car suddenly loses power, as if it were not getting enough fuel. After the dealer had the car a week, he replaced the igniter, but that didn’t fix the problem. Another mechanic replaced the fuel filter, which worked fine for about a month. Then the problem returned. Any suggestions?--P.C.

A: The igniter, which is a part of the electronic ignition, was the wrong thing to replace, because when it fails the car simply dies. The mistake is so basic that you may want to look for a new mechanic.

Because the new fuel filter fixed the problem temporarily, it’s a good bet that the fuel system continues to have a problem. If the new filter is again clogged, you may have a contaminated fuel tank. In that case, you need to have the tank removed and cleaned.

If the fuel system is not clogged, then you should have the fuel injectors checked. Possibly they are clogged, because it takes a lot less dirt to foul that system than to plug the filter.

You should also have the fuel pump checked out to make sure it has not been damaged or is unable to provide adequate fuel volume and pressure. A mechanic can easily check that with a fuel pressure gauge and by performing a volume test.

Vartabedian cannot answer mail personally but will respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, You section, The Times, Times Mirror Square, Los Angeles 90053.