Premium vs. Regular


My car runs on regular. Will "treating" it to premium gas provide any benefit?

My owner's manual calls for premium. Do I really need to use it?

What is pinging or knocking?

How does high-octane gas prevent pinging or knocking?

Is it a big deal if my car pings?

Are there any circumstances under which premium gas would be a good idea?

Q. My owner's manual says my car will run just fine on regular, unleaded gas. Will "treating" it to premium gas provide any benefit?


A. Let's be perfectly clear about this:


A. The only thing you'll be benefiting are the portfolios of impoverished oil company executives.

And before you do that, consider that Exxon-Mobil earned $39.5 billion dollars in 2006 - a world record profit. It's not like they need you giving them a hand out.

Q. But, won't premium increase the performance of my car's engine?



A. Higher octane provides no additional performance for cars that are designed to run on regular gas.

Q. You're telling me I'm wasting my money by using premium?



A. You're starting to get the picture.


Q. Okay. My owner's manual does call for premium gas. Do I need to use it?


A. In that case, the answer isn't quite so clear. In a high-compression engine that's designed to run on premium fuel, premium will provide some additional power. But, if you want to save some money, you can probably still fill up with regular, unleaded fuel much of the time.

Q. How much will I save?


A. About 20-30 cents per gallon. For an average driver, that can run as high as high as $200 a year.

Q. So, why would my owner's manual calls for premium gas instead of regular?


A. Because your manufacturer decided to use what's known as a "high compression" engine.

An engine with a high compression ratio has some advantages. It squeezes more power of the same-size engine. But, it requires you to spend more for every tank of gas, to get that extra power. In other words, instead of manufacturing a car with a larger, but lower-compression-ratio engine, manufacturers are using high compression engines, and foisting the additional cost back to you - by forcing you to buy premium gas to get that extra performance.

Q. My owner's manual says that if I don't use premium, I might get engine pinging or knocking. Is that right?


A. It's possible, depending on the load you put on the engine.

Q. What is pinging or knocking?


A. They're noises, which are signs that the gas and air mixture in your car's cylinders isn't burning exactly as intended. The sound you hear is the result of the fuel and air mixture combusting unevenly in the cylinder.

Pinging or knocking will reduce the efficiency of your engine and, over a very long period of time, it can cause damage.


Q. How does it occur?


A. Let us show you! Here's what's going on in the cylinders inside the engine during pinging or knocking:

Illustration #1 The piston begins to move upwards during what's called the, "compression stroke," compressing a mixture of fuel and air.

Illustration #2 In a normally operating engine, the spark from the spark plug ignites the mixture of fuel and air, causing an extremely rapid burning of the fuel in the cylinder. That's good. It's what creates the pressure that makes the piston travel down very fast, causing the crankshaft, your transmission, and ultimately the wheels - to turn.

Illustration #3 However, it's possible for the mixture of gas and air to burn somewhere else in the cylinder, simply from the pressure (or compression) within the cylinder, and not from the spark. That's called "pre-ignition," and it's more likely in a high-compression engine.

Illustration #4 When the fire you want (that's the one from the spark plug), collides with the fire you don't want (that's the one resulting from the pre-ignition), the result is a ping or, if the pre-ignition fire is big enough, a knock. The degree of severity, including the amount of noise generated, is determined by how big that unwanted flame is.

Q. How does high-octane gas help?


A. Compared to regular gas, high-octane gas requires higher temperature and pressure to ignite, so it can withstand higher compression without reigniting. As such, it's less likely to result in premature ignition, and therefore prevents pinging and/or knocking.

In other words, it's a form of protection for high compression engines.

Q. So, I should use high-octane gas to prevent pinging?


A. High-octane gas will prevent pinging.

But these days most cars have something called a knock-sensor, that will - under many circumstances - obviate the need for premium gas. Just about any car that's more recent than about 1996 will have a knock sensor.

Q. How does a knock-sensor work?


A. The knock-sensor uses auditory detection to actually "hear" the knocking or pinging. When necessary, it uses this information to delay the spark and to minimize knocking or pinging.

That's good news. That means you can use gas with a lower octane rating. And, if your engine detects a knock or ping, it can usually adjust the timing of the spark until the knocking is gone.

Q. You're telling me that modern cars automatically detect this problem, and therefore won't ping?


A. Right - as long as the load is not too great.

Load is the amount of work you're asking the engine to do, and it's affected by a number of factors, including climbing steep hills, pulling heavy weight, hard acceleration or driving in hot weather. Any combination of these factors can affect load. So, if you live out in the desert Southwest, it's 115 degrees out and you're hauling your mother-in law up, you're going to need premium.

Why? Because there's only so much that your car's knock sensor and computer can do to adjust the engine's timing.

Q. Is it a big deal if my car pings for a few seconds here and there, under these circumstances?


A. No, it's not.

Q. So, are there any circumstances under which premium gas would be a good idea?


A. If you plan to haul that aforementioned mother-in-law in hot weather, or are going to be driving up monstrous mountain passes with a heavily laden car, then you might consider filling up with a tank of premium gas.

Q. But, under most normal operating conditions, do I lose anything if I use regular unleaded instead of premium?


A. In many cases, no, but you'll have to experiment with your own car. If you take our advice and drive judiciously - without lead-footing or overloading your car - and you don't hear pinging, you can use regular fuel. Of course, you'll lose that warm feeling of giving oil companies an average of 20-30 cents more per gallon of gas. And, you will lose performance that under most driving situations won't be noticeable.