What Are the Numbers on Gas Pumps?

As drivers in the Sterling, Virginia area, we all fuel up our vehicle’s gas tanks multiple times each month, often doing so without considering what the numbers on the fuel pump genuinely represent. Some prefer the cost-effective route afforded them at pump number 87. Many are creatures of habit who believe the highest octane is worth the investment for the longevity of their vehicle’s life, regardless of the make and model.

If you have ever asked yourself what the numbers on gas pumps stand for, why the gas pump numbers matter, or if gas pump numbers are essential for the health of your car or truck, this blog is for you!

To gain a better understanding and provide your vehicle with the best automotive care you can give it, let’s take a trip into the internal combustion engine of the average modern vehicle.

Engine Cylinders, Pistons & the Crankshaft

Vehicles with combustion engines contain cylinders and moving pistons connected to crankshafts. Once ignited by the spark plug and expanding combustion gases, it pushes the piston, which in turn rotates the crankshaft.

A cylinder is a chamber where the gasoline is burned and turned into power; it is the central working part of an engine and is the space in which the piston travels. The number of cylinders in a vehicle varies, and most engines have four, six, or eight cylinders. If this sounds familiar, it is most likely because you have at one point or another heard someone say their vehicle has a four-cylinder, V6, or a V8 engine. Those multiple cylinders are commonly arranged side by side in a bank, or engine block.

Gasoline and Air

Inside the cylinders are where the mixture of gasoline and air burns. When you have the correct octane fuel in your gas tank, the spark plug ignites the mix, and the pressure from the resulting explosion pushes the piston down. If the fuel in your tank is not an optimal match for your engine, the heat can ignite the fuel before the spark plug fires.

If the fuel ignites before the spark plug, the early ignition can cause waves of pressure that rattle the piston creating a knocking sound. All that action causes the spark plugs to overheat, erode the chamber, and, ultimately, poor engine health.

Octane Numbers

The gasoline found at the pumps is lab-tested by way of comparison with two reference fuels.

One reference fuel is knock-resistant and, when numbered on the resistance scale, has a rating of one hundred (100).

The other reference fuel knocks easily, and its rating is zero (0).

Octane numbers determine the likelihood of knocking within an engine.

The two fuels are combined to make the reference fuels that will be used as a basis of comparison for the gas you are buying at the pump.

As fuel arrives at the lab for testing, it gets compared to the reference fuels. When a fuel acts as a comparison mixture (reference fuel) with 87% knock-resistant fuel, it gets labeled with an octane number of 87. The same goes for 88-90 and 91-94. In other words, the higher the octane number, the more resistant it will be from causing a knock.

What Your Vehicle Requires

While knocking depends partly on the engine’s compression ratio, some engines need higher octanes to avoid as much. If you have been using a lower octane on your vehicle without having heard your engine knock, there probably is no need to spend more money at the pump than necessary. However, being the best automotive repair shop in Sterling, VA, we always recommend that you refer to the manufacturer’s manual, where you will find the octane best-suited for your vehicle’s engine. If it cannot be found in your manual, give the manufacturer a quick call or do an online search.

Above all else, pay attention to your vehicle. Take notes of every sound, scent, and noise you might notice for reference when visiting your automotive shop. If you suspect you hear your engine knocking, come on by Casey’s Automotive. Our teams of certified technicians in Sterling, VA, and Chantilly, VA, can service your automotive needs. Make sure you take advantage of our Winter Special before it is too late! Contact us today at (703) 444-6900 to make an appointment.

The best referral you can get is from a neighbor.