can you put 89 in 87 car

[EmmaLynn]

Yes, you can physically put 89-octane fuel in a car designed for 87-octane. It will not harm your engine. However, for the vast majority of cars requiring regular 87-octane fuel, using a mid-grade 89-octane is an unnecessary expense that provides no performance or fuel economy benefits. The key is to follow your manufacturer's recommendation, which is based on your engine's compression ratio and its specific anti-knock requirements. Using a higher octane than required is essentially paying a premium for no tangible return.

Octane Rating Explained The octane rating, displayed as AKI (Anti-Knock Index) on U.S. pumps, measures a fuel's resistance to premature combustion, known as engine knock. High-performance engines with high compression ratios require higher-octane fuel to prevent this damaging knock. Standard engines are engineered to run optimally on 87-octane.

Performance and Cost Implications Your car's engine control unit (ECU) is calibrated for 87-octane. It will not advance the ignition timing to take advantage of 89-octane's higher resistance to knock. Therefore, you won't experience more horsepower or better mileage. You are simply spending more per gallon. Over a year, this can add up to a significant, unnecessary cost.

Scenario	Fuel to Use	Rationale
Manufacturer Recommends 87	87 (Regular)	Optimal for performance and cost. Using 89 provides zero benefit.
Manufacturer Recommends 91+	91+ (Premium)	Required to prevent engine knock and potential damage.
Occasional Mixing (e.g., only 89 available)	89	A one-time fill-up with 89 in an 87-car is perfectly safe.

Stick with 87-octane unless your owner's manual or a sticker inside the fuel door explicitly states otherwise. It’s the most economical and effective choice for your vehicle.

[LeLondyn]

Think of it like this: your car's engine is designed for a specific "diet." If the manual says 87, that's what it needs. Putting in 89-octane is like feeding it premium food it can't digest. The engine's computer is smart, but it's programmed for 87. It won't magically adjust to make the more expensive gas work better. You're just burning money for no reason. Save your cash and use the recommended grade.

[OFernando]

From a mechanical standpoint, the risk of damage is virtually zero. The higher octane simply raises the fuel's resistance to detonation. Since your engine isn't prone to knock on 87, the 89 is overkill. The engine's sensors and computer will detect no knock and maintain the standard ignition map. You won't see any gains in horsepower or fuel efficiency because the engine isn't under the stress that requires a higher octane. It's a financial loss, not a mechanical one.

[McAlivia]

I used to think higher octane meant a cleaner engine or better performance—it's a common myth. After looking into it, I learned octane has nothing to do with cleaning power or energy content. It's purely about controlling combustion. Premium fuel often has the same detergent additives as regular. So, for a car that takes 87, you're not getting a "cleaner" burn. You're just paying for a chemical property your car doesn't need. I stick to the manual now and save a lot at the pump.