What Happens If You Fill Your Car With the Wrong Octane Gasoline
Even though I drive several different cars, I always get a little worried when it’s time to refuel. Does something happen if I use 87 instead of 93 or vice versa? In short, it depends on the circumstances.
The first thing you should do is check your vehicle manual to see what octane it recommends, according to a Ford Motor Company engine development engineer . Ideally, use this one.
Great, but what if you mistakenly use a different octane number? Three levels of petrol (RONs 87, 89 and 93) are located next to each other on the pump, making it easy to absently press the wrong button.
Using a higher octane number than necessary
If you choose a higher octane number than the manual recommends, say 89 instead of 87, your machine will be fine, explained in an article on the AAMCO blog . However, according to Car Talk , it won’t improve your vehicle’s mileage or give it any additional performance boost. The only thing is that it will cost you extra money, so don’t do it.
Using a lower octane number than required
This is where things get tricky. A Ford engineer says that using a lower octane rating than what is recommended in your car manual poses a big risk: it might be good, but you could damage your engine as well. Sensors in modern engines can adjust the ignition system to operate on lower octane gasoline, but only under “stable conditions,” such as driving on the road or steadily driving uphill.
In the words of our friend at Ford :
“Transitional conditions are the problem. Since it takes time to analyze the knock sensor signal, rapid changes in load or engine speed are difficult to prevent. Every automaker will be different in this regard, as the ability to quickly analyze this knock depends on the skill of the programmers and calibrators and even the speed of the PCM processor. Thus, if you fill up with a fuel with a lower octane number, and then drive the car abruptly, quickly press the accelerator pedal, you can get a severe shock and possible engine damage. I will say that this is unlikely to really happen with cars produced in the last few years, but you are certainly exposing your engine to the possibilities. ALWAYS, ALWAYS, ALWAYS use the fuel recommended in your vehicle manual or any sign on the fuel filler door or cap. When engineers say to use a specific fuel, we have good reasons. ”
What to do if you are using the wrong octane number
According to the folks at Car Talk – who have checked with people at the American Petroleum Institute and the American Engine Manufacturers Association – intermittent use of gasoline with a lower octane rating than your car requires is unlikely to damage your engine. Therefore, if you accidentally press the wrong button on the pump, make sure to use the correct octane number next time.
Watch your ear to avoid knocking or knocking, which could be a sign that the gas / air mixture in your car’s cylinders is not burning as intended, explained in another Car Talk article . It goes on to say that this noise or knock will make your engine less efficient and can cause damage “over a very long period of time” – so one miss is probably enough.
This story was originally published on 8/25/16 and updated on 7/26/19 to provide more complete and up-to-date information.