How Can Your Choice of Gas Affect Your Vehicle


Whenever you pull into a gas station, you’re faced with a choice: do you fill your tank up with regular, or do you splurge on the premium? With words like “super” and “plus” plastered to the front of the pump, you might think that the higher the octane, the better it must be. And as the owner of a BMW, you want what’s best for your car – so premium is the way to go, right?

The truth is slightly more complicated than that, and, depending on the model of your car, paying for premium might not be doing anything to improve its performance. To help clear the confusion, let’s review the differences between regular and premium gas, and find out when you’re actually better off using high-octane fuel. More important that the actual octane rating is the actual stations at which you buy your fuel. Top Tier gas stations like Chevron, Mobile, Shell etc sell gas that has a cleaning additive in the fuel that keeps components clean. So an 89 at Chevron will be better in the long run for your car than a 91 at other gas stations. Check and make sure your station is a top tier station and that there is more in their gas than just gas.

Regular vs Premium: What’s the Difference?

The difference between regular and premium fuel is in the octane rating, which tells you how much compression the fuel can withstand before it combusts. Low-octane fuel can tolerate lower amounts of compression than high-octane fuel. If your car has a high-compression engine, then you’ll benefit from filling up the tank with premium gas.

Some BMWs have high-compression engines, while others don’t. The best way to determine whether your car calls for premium gas is to check your owner’s manual.

So, what might happen if you choose the wrong fuel for your car?

The wrong fuel can…

… create a whole lot of noise

If you have a high-compression engine, low-octane gas can cause “knocking” – a pinging sound that occurs when the mixture of air and fuel in your engine isn’t burning correctly. Under normal circumstances, the air-fuel mixture is ignited from the spark generated by the spark plug. When you hear knocking, though, this means that the air and fuel are burning up somewhere else in the engine, due to the compression in the cylinders. In other words, using the wrong fuel can make your engine really noisy – and, sometimes, that noise can lead to serious problems.

… cause engine damage

Most modern knock-sensors in cars that require premium fuel will correct for low-octane gas, but no necessarily in all conditions.  Long-term knocking can negatively affect your car’s performance, and possibly damage your engine. While serious internal damage isn’t guaranteed when you use the lower-octane fuel, it’s still a risk. If you’ve been experiencing engine knocking, a technician can help you correctly diagnose the source of the problem – whether that’s the octane level of your fuel, or something else more serious.

…result in a failed emissions test

Another part of your car that can be affected by your choice of gasoline is the oxygen sensor. This small but vital component monitors how much oxygen is in your car’s exhaust, helping to increase performance and decrease harmful emissions. Using low-quality fuel that lacks a cleaning agent, or using a lower octane gas than is recommended for your car, can cause your oxygen sensor to fail. And if that happens, you could fail your emissions test.

… decrease your car’s efficiency

If your oxygen sensor malfunctions, you may also likely experience a reduction in gas mileage – but you won’t always notice it until it’s too late. The biggest problem with a failed oxygen sensor is that it can be hard to diagnose. Sometimes, a broken oxygen sensor will trigger the check engine light – but sometimes, it won’t. To make sure it’s always functioning as expected, fill up with a high-quality fuel.

B and B Autohaus can help extend the life of your BMW

At B and B Autohaus, we aim to educate our clients on how to properly care for their BMWs – including choosing the right gas to help them avoid costly repairs down the line. With decades of combined experience working on BMWs, our technicians and mechanics are among the most highly qualified in all of San Diego. Call us today at (858) 560-0042, or check out our Kearny Mesa shop, and experience the B and B difference.