Total Kar; Cars, Trucks and Mechanics

Q: I drive a 2008 Acura turbo RDX. Acura recommends the higher octane grade gas. Can I go to the lower octane too? Does Turbo make a difference in gas selection?

A: I have to agree with Acura here… minimum octane rating for your engine (2.3 liter 4 cylinder with 240 horsepower) is 91.

Premium fuel is part of a turbocharged gasoline engine. Understand this; it is not that your engine won’t run on lower grade fuel, it will, however you won’t get proper performance from your engine with a lower grade gas. You will have less power and you will not be able to gain RPM as easily. This will make the engine actually use more gas to get the same performance as with a higher grade gas.

The biggest problem however will be the fact that you may also get unwanted noise from your engine (knocking or clattering). Your engine has a “Knock Sensor” that will sense this and it will attempt to adjust ignition timing to eliminate or reduce the knock. Long term knock can be damaging to your engine.

So though you might think you save money by buying lower grade gas, you in fact will do the opposite, you will end up spending more on gas and on possible engine repairs.

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When you go to the gas station to fill up your car, there is always the choice of three different levels of octane gas, from low to high. Why are there different levels, and which one does my vehicle need?  These are good questions. First let me explain a bit what it is, octane…

When gas is sprayed into the engine, the heat of the engine turns the gas in to a vapor. The spark plug sets of a spark to ignite this vapor. Sometimes however, the gas mixture detonates to early, when this happens you often hear an extra sound, called a ‘knock’.  Octane is an additive put into gasoline to control unwanted knocking. The higher the level of octane, the less likely knocking occurs.

Why then three different levels of octane and not just one level; high?

Higher octane fuel burns slower, which in turn gives more thermal energy, so you should get more power from higher octane fuel. But the byproduct of a hotter engine is more carbon waste and it won’t clean your engine out, just the opposite…

Then, why not one level; low?

Lower octane actually burns cleaner; however, if hauling heavy loads, especially on hilly or mountainous terrain, your car or truck won’t perform as good as it does with higher octane level. The three different levels are to suit the different needs.

Most all vehicles today are engineered to run on the lower octane rating, after all, less emission is supposed to be the main motivation for the engineering of today’s cars and trucks. In normal situations I run a lower level octane, to spare my engine and the environment. However, if I need just a bit more performance I will run a higher octane level.

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