Why do you pay more for higher octane gas?

Question

I was thinking of buying a Pontiac GTO but I know that it requires 91 octane gasoline. My question is what would happen if you put 87 gasoline in any car that requires 91? Would that ruin your car or what?

Answer 1

If the manufacturer tells you that the higher octane is REQUIRED, then you must purchase the higher octane. If the manufacturer tells you that the higher octane is RECOMMENDED, then you have the option to purchase the lower octane because the manufacturer has installed a knock sensor.

While I tend to agree with Red above, he is incorrect in stating that it won't ruin your car if you use the lower octane. if the manufacturer REQUIRES the higher octane you must use the higher octane to prevent engine damage.

Octane values are values to indicated the fuels pre-ignition qualities. The higher the octane number, the harder it is to ignite the fuel.

Lower octane fuels can auto-ignite due to hot spots in the cylinder chamber during the compression process. This causes flame fronts to be generated from other locations in the cylinders other than the flame front that is coming from the spark plug location. When these flame fronts collide, actual shock waves are generated. These shock waves are typically hear and called "Engine Ping" Over time these shock waves can significantly damage engine pistons and cylinders.

Most manufacturers realize that people are too cheap to pay for the expensive gasoline, and obviously want to move their vehicle. Many manufacturers now have knock sensors placed on the engine. The knock sensor tell the engine computer to basically retard spark when engine knock (pinging) is detected. The retarding of spark, basically fires the spark plug at a point less than optimal. (or earlier in the compression cycle to prevent the pre/auto ignition). This also really defeats the purpose of developing a more powerful engine for the cars.

However if your vehicle REQUIRES 91 octane, it means no knock sensor is on your engine and using anything less will cause engine damage.

From an economic stand point, most of the time 91 octane is $0.10 (ten cents) more than the (87 octane). A Pontaic GTO carries approximately 18 gallons of fuel. So each fill up is only going to cost an additioinal $1.80 more than the regular stuff. If the manufacturer REQUIRES the higher octane fuel, your still spending less than the cost of a cup of coffee at Starbucks!

If your purchase the GTO, it's a beautiful car, good luck, but don't ruin it to save a few bucks.

Answer 2

I have a customer at my shop with a Nissan Maxima that requires 92 octane gas. He always puts 87 in it to save money. At about 35k miles he started getting check engine lights for a Catalyst Efficiency Low code. He would come in, have us pull the code. We would tell him what it was and tell him he would ruin the Catalytic Converter if he didn't switch to the recommended 92 octane. He refused and every 2-3 months would be back with a Check Engine light and the same code. At around 50k miles his catalytic converter went **** up and it cost him something like $800 to replace as I recall.

So much for saving $0.20 a gallon on gas.

Answer 3

It won't ruin it it will just not perform and it will ping due to preignition , your car was designed for 91 and it needs that for performance which includes gas mileage.

You pay higher costs due to the extra additives and refining required for 91 octane.