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What Level of Octane Should I Use in my Car?

When you pull up to the gas station with an empty fuel tank, it is tempting to simply choose the lowest price tag. Unfortunately, reaching for regular grade fuel may not always be the best choice. You need to consult your owner’s manual or the sticker on your gas cap to determine the right octane for your vehicle. Or, call a professional auto repair shop in White Lake, MI. Here is what you need to know about octane at the pumps.

What is an Octane Rating?

It shows the fuels ability to be compressed without prematurely igniting in the engine. Gas and air get compressed inside the cylinders. Then, once they are under pressure, a spark ignites the fuel. This controlled explosion creates the combustion to power your vehicle. But different makes and models compress the fuel and air at varying ratios. High performance vehicles with bigger horsepower usually have higher compression ratios. So for higher horsepower you want a high-octane fuel. It does not ignite as easily and can withstand more compression.

What Happens When I Use a Higher Octane?

If you use a high-octane fuel instead of a specified lower octane, nothing will happen. It will not harm the engine and will not give your engine any more power. The worst scenario is that you wasted a few bucks at the pump buying more expensive fuel.

What Happens When I Use a Lower Octane?

If you put lower octane gasoline in a vehicle that requires higher, you might notice some issues or you might not. Most cars have a modern knock sensor that can automatically adjust the timing for lower octane fuel. That said, it usually only works for standard driving conditions, like driving steadily uphill or cruising down the road.

Fast changes in engine speed or load is where you will likely notice a change. If you put in the lower octane gasoline and press the accelerator quickly, you will likely experience a heavy knock. If you continue to drive roughly with a lower octane fuel, it can result in engine damage.

What Causes an Engine Knock?

Basically, it is a misfire. In a spark-ignited engine, combustion inside the cylinder starts at the spark plug and propagates outward. The end gas, or unburned portion, experiences increased temperature and pressure. If that increase is too high, the end gas of a lower octane fuel will spontaneously combust. It is a very fast and violent reaction that causes the knocking sound you hear. And while putting a lower octane fuel isn’t as serious as mixing up diesel fuel and unleaded, it could still cause problems.

Choosing the Proper Octane for Your Vehicle

Always use the proper fuel recommended in the owner’s manual or on the fuel door or cap of your car. It is there for good reason. And if your manual specifies a higher octane, choose the closest octane without going below it. If you do happen to fill up your tank with a lower octane, go to a local parts or auto repair shop in White Lake, MI for an octane boost. One bottle should treat an entire gas tank, getting the octane rating up to where it should be. Granted, this isn’t a fix-all solution and shouldn’t be used on a regular basis, but it can help you out in a pinch.

If you have more questions about octane and gasoline, call Holly Tire. We offer honest and reliable auto repair in White Lake, MI. You can reach us or swing by 15140 N. Holly Rd. Holly, MI 48442 to talk with one of our technicians.


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