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[hystria]

Originally Posted by fu_im_from_texas

"....using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit.

TRUE. As per Yaris manual, it recommends 87 or higher. Why "or higher" ? Ever wonder why Toyota recommends wasting your money ? With NO REASON ? Is Toyota in business with Shell ? Well, if not, there should be a reason, unless there are places on Earth that sell only 89 or higher octane gasoline... don't think so...

Engines are optimized to run with a precise level of octane. If an engine requires 87 and the owner put 89 or higher, there will be absolutely no benefit for the engine. On the other hand, if and engine is optimized to run with 89 and the owner uses 87, the engine will not run at 100% performance. It will knock more or little because the mixture ignites before the optimum moment during compression, thus leading to hot points on the piston/ring surface. Because the mixture ignites before the moment when the engine compression is optimal, it produces less overall performance. But not by much, one will not be able to feel any difference.

To resume... if using 87 the engine starts knocking, try changing the brand... the Yaris engine should not be knocking to an audible/damageable level while using good quality 87 octane gasoline.

[Pavel Olavich]

Originally Posted by hystria

TRUE. As per Yaris manual, it recommends 87 or higher. Why "or higher" ? Ever wonder why Toyota recommends wasting your money ? With NO REASON ? Is Toyota in business with Shell ? Well, if not, there should be a reason, unless there are places on Earth that sell only 89 or higher octane gasoline... don't think so...

Engines are optimized to run with a precise level of octane. If an engine requires 87 and the owner put 89 or higher, there will be absolutely no benefit for the engine. On the other hand, if and engine is optimized to run with 89 and the owner uses 87, the engine will not run at 100% performance. It will knock more or little because the mixture ignites before the optimum moment during compression, thus leading to hot points on the piston/ring surface. Because the mixture ignites before the moment when the engine compression is optimal, it produces less overall performance. But not by much, one will not be able to feel any difference.

To resume... if using 87 the engine starts knocking, try changing the brand... the Yaris engine should not be knocking to an audible/damageable level while using good quality 87 octane gasoline.

The "or higher" phrase only means that if 87 is not available, then using a higher octane is not going to damage your engine.

Don't be so quick to read more into the words, then what is literally meant.

Also, to suggest as a remedy, to use higher octane than called for in the manual, a way to remove knocking is plain wrong. It would be far better to take the car in and determine why it is knocking at the required octane, and to remedy the problem. Going up in octane is a band-aide that only masks a real problem.