What happens if I don't use the recommended fuel for my car?

Our tech guru has the answers to your questions
by Ferman Lao | Dec 12, 2014

Hi, Top Gear. I just picked up my Ford EcoSport. I asked my sales agent what kind of gasoline I could fill up with, and she said unleaded fuel. So I loaded P1,000 worth of 91-octane unleaded gas. When I got home, I studied the owner’s manual and saw that the recommended fuel is 95-octane. My question is, will my one-time use of 91-octane damage my car? Today, I filled the tank with 97-octane Shell V-Power Nitro+ Racing so it would mix with the 91-octane.

Lance Asprec


No, it won't. Using a lower-octane fuel in most modern cars just means you're not getting optimum performance or efficiency. The octane rating is a means to determine the ‘knock’ or self-ignition resistance of the fuel. The higher the number, the more knock-resistant it is.

High-octane fuel actually burns slower--or in a more controlled manner--than lower-octane fuel in the combustion chamber. This allows the tuning of an engine to be more aggressive for maximum performance. The computer-programming of most modern vehicles has the capability to compensate for octane rating (up to a point). When it detects that the engine is knocking (sometimes, even when it is inaudible to us), it will automatically adjust the tuning of the engine to the fuel quality to prevent any damage. The trade-off is that the engine will not be producing as much power as it should be had it been running on a higher-octane fuel. This also results in poorer fuel consumption or less kilometers traveled per liter of fuel consumed, so it is best to use the recommended fuel to get the most out of your engine.

Continue reading below ↓

You can mix fuels with different octane ratings. The result will just be a lower octane than that of the higher-rated fuel you put in--but higher than the lower-rated fuel you used. The lower-octane fuel will be purged from your tank soon enough under normal use.

And good job on reading the owner’s manual. You're one of the few who actually do. There's a lot of information in it on how to keep your car running well.

Ferman Lao
Technical Editor

Do car problems keep you awake at night? Send questions to topgear@summitmedia.com.ph.

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    TGP Rating:
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