Should I Use Premium Gas in My Car?

Updated on January 3, 2020
Ian Mundell profile image

Ian is a car enthusiast who's driven cars, motorcycles, and trucks all over the world and still loves to drive a manual transmission car.

Do I Need The Most Expensive Grade of Gas?

There are a lot of stories, legends, and myths about what kind of gas you should use in your car. You've probably heard the most common stories:

  • if you use premium gas, you'll get better mileage;
  • your car will last longer if you use higher octane gas;
  • the more expensive gas grades will give your car better performance.

In this article we'll go into all these points and talk about what you should know, what is the best kind of gas to use, and when some of these stories might actually be true!

What Are the Different Grades of Gas?

Every time you drive past a gas station, or stop to fill your car or truck, you'll see three (and sometimes even four) different grades available. These are two obvious differences between the grades:

  • Names - they'll have names like regular, mid-grade, and premium.
  • Prices - this is the most important difference! The range between the cheapest and most expensive grades can be 40 cents or even more.

But beyond price and name, what do those numbers actually mean, and should you care?

Source

Octane and Compression

The good news is you don't need to know all about how a car engine works to figure out if you need the expensive premium gas. However, if you've ever wondered about what those numbers mean, the next section is for you.

A traditional car uses an internal combustion engine, and it works like this. A mixture of gas and air is compressed by the motion of a piston inside a cylinder. When it's compressed to a certain point, a spark sets it on fire and the tiny explosion sends the piston back up the cylinder. There are several cylinders, each with a piston, and every one is pumping up and down to keep producing power for the car.

In a modern car engine this is very precisely timed, but there's still sometimes some fuel that, because of the high heat produced by this action, might detonate ("self ignite" or "pre-ignite") before the spark sets it off at the exact right time.

The octane rating of gas is a measure of how good it is at resisting that self ignition. The lower the rating, the more likely it is to self ignite.

What Happens if Gas Self Ignites?

The problem isn't so prevalent these days (I'll explain why in a moment). But think about what's happening. A potent fuel is exploding (in a very small way!) in a semi-uncontrolled fashion. As with any explosion, it causes vibration and shock waves, which can ripple throughout the car engine. You'll notice this as a knocking or a pinging sound. Imagine repeatedly hitting your car's engine with a small hammer - it'd have a similar effect. If a lot of knocking occurs, it could potentially damage the engine.

Thankfully, with today's computerized cars, this is much less problematic than it used to be. The computers in a car can detect self ignition and knocking, and can change the timing of the pistons and the sparking so as to reduce

Where Does The Octane at the Pump Come In?

Modern technology has made huge changes in how car engines perform, and they are much more capable of self correcting for minor problems today. That also means they don't have to have a very high compression ratio, unless you have a car which is designed to be very high performing - in other words, a sports car.

Higher compression means more heat, and that means more likelihood of self ignition for unburned fuel mixture before the spark gets to it. But with modern cars being so reliable, coupled with car computers that can detect knocking and make necessary changes to reduce it, it's only the most demanding applications that will notice a difference between premium and regular octane grades.

What's the Cost?

The cost of regular versus premium isn't all that much. If you drive 15,000 miles a year, filling up on premium will only add about $20 a month to your gas bill.

You (Probably) Don't Need Premium Gas

So if premium gas is better at resisting self-ignition, who needs it? Most cars just don't have the high performance requirements (meaning a high compression engine) that will cause knocking in a modern engine - and preventing that knocking is why you need the high octane gas. Only a small number of vehicles really need it, and these are mostly sports cars.

  • Read your car's manual. Some manufacturers will say premium gas is recommended or suggested, but if it's not specifically listed as required then you can start with unleaded gas and it'll almost certainly work fine. Remember, the majority of cars are designed to use regular gas.
  • Listen for knocking. If you hear knocking, bump up to the next grade.

Using premium gas won't give you better mileage, and for most cars it won't make any noticeable difference in performance. For most drivers, the only effect you'll see is a higher charge at the pump.

Bottom line - follow what it says in the manual. If it says premium is required, then you'll have to spend a little more at the pump. (But it's well worth the extra money to protect against possible engine damage.) If it says something more lenient like "premium recommended", you should be fine with regular.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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    © 2020 Ian Mundell

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