By Roland Jones Business news editor
msnbc.com
updated 7/23/2008 1:25:25 PM ET 2008-07-23T17:25:25

With gasoline prices hitting record highs almost daily, you might be wondering if you can get away with filling up your expensive car with regular instead of the expensive premium gas your manufacturer recommends.

The answer: Regular’s fine in most cases, but it’s best to check your owner’s manual.

Given the high cost of a fill-up these days, Americans in almost every income bracket are cutting back, and those who drive high-end vehicles that demand premium gas are paying a higher price.

“In the vast majority of cars out there you can get away with using regular gas instead of premium, but there are a few hot rods like the Dodge Viper that require you to use it all the time,” says John Nielsen, director of the AAA’s Approved Auto Repair and Auto Buying Network.

“If it’s required, you’re often going to see that word in the owner’s manual, and that’s going to be very clear, but if it says premium is ‘recommended’ you can probably use something less expensive without any damage. So the best advice we can give to drivers is to check if their car requires premium gas by looking in their owner’s manual,” he said.

There are three basic provisos for gasoline usage in owner’s manuals: when only regular gas is required, when premium is “recommended” and when premium gas is “required.” Only in the third instance will deviating from the manufacturer’s requirements potentially harm your car, said David Champion, director of automobile testing at Consumer Reports.

Using premium gas in a car that only requires regular won’t help performance. As for cars for which premium gas is recommended, but not required — such as the V6 Nissan Maxima, the Toyota Camry V6 and Nissan Murano — using a higher-grade gas like premium will give you better engine performance, but not significantly better mileage, Champion said.

But if premium gas is required, those cars are designed to run only on premium and could possibly be damaged if you use regular over a prolonged period, Champion said. Cars that require premium gas are typically made by luxury brands like BMW, Mercedes, Lexus, VW and Audi, and some Acuras are also on that list, he said.

Video: A gadget that saves gas

At certain temperatures and altitudes, you might want to use premium because there could be some ‘pinging’ or engine ‘knock’ and there will be a slight loss performance, and the impact on the engine can sometimes be significant, he added. “So if premium is required, you could try using regular, and if [the engine] starts to ping use premium.”

Premium gas’ name is in some ways misleading. Premium doesn’t mean higher quality, it means higher octane, a term that measures how quickly a fuel burns (the higher the octane, the slower the burn).

A fuel’s burn rate used to matter because it controls the amount of engine “knock” or “pinging,” which refers to premature ignition of the fuel-air mixture inside the engine’s cylinders (it makes a sound similar to marbles inside an empty can). Occasional knocking is fine, but prolonged knocking can seriously damage an engine, according to AAA’s Web site, and so higher-octane, slower-burning gas is recommended to control it, especially in older cars.

But if you use regular gas in a modern car that requires premium, the potential for engine damage is somewhat limited because most of them now have a device that can sense engine “knocking” and can compensate for it to prevent any damage by automatically adjusting the car’s settings to a lower-octane gas.

Mid-grade gas is cheaper than premium, but it isn’t worth bothering with, said Champion. Regular gas has an octane level of 87, while mid-grade usually has an octane level of 89 and that is not sufficient for cars that require premium gas, which generally has an octane level of 91.

In the end, lowering the octane level of your gas will offer a modest saving. While the precise price difference between regular and premium gas changes depending on market conditions, AAA calculates that the current price spread between self-service regular and self-service premium is approximately 40 cents per gallon on a nationwide average basis.

So with regular gas at about $4 a gallon, that’s a saving of 9.5 percent of your fuel bill each time you visit the gas pump, said Jeff Sundstrom, AAA’s fuel price analyst.

Far more important than using regular or premium is the type of gas you put in your car, Sundstrom added. AAA advises using a major brand of gas that includes a detergent like Chevron’s Techron, he said. Detergents keep engine valves and fuel injectors free from the build-up of carbon deposits that can reduce an engine’s performance.

Another effective way to save on gas is to drive like your grandmother, said Champion. That means gentle acceleration, gradual braking and avoiding hard stops, he said. Accelerating too quickly can mean you have to brake harder and that can waste gas.

“Drive like your grandmother and your gas mileage will go up noticeably,” he said. “No changes you make at the pump can do that for you.”

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