Is There Actually a Benefit to Putting High Octane Fuel in a Low Octane Engine? • Cars Simplified


Is there any benefit to running a higher octane fuel in your car if it only calls for low octane? Hi I’m Steve and you’re watching Cars Simplified and I’ll answer that question for you right now: the answer is no there are plenty of videos that cover that, but there’s one exception that a lot of them don’t cover. Just in case you don’t know why the reason is no, the basics of it is that you don’t want to compress the fuel beyond the point where it just spontaneously combusts based on
compression alone. Diesel engines do this but it’s timed specifically so when the piston is at the top, then that’s when it combusts, and then the piston can come down. The problem in the gasoline engine is that it’s not supposed to do that, it’s supposed to ignite when the spark plug fires. And if you have a high compression engine, you compress that air and fuel and it detonates before it’s time; it’ll actually detonate while the piston is still coming up and you’ll get pinging or knock or detonation… It’s not a good thing. So, if you have a high compression engine you want that high octane fuel so it doesn’t ignite prematurely If you have a low compression engine then you can run a lower octane fuel and not worry about that. Now we’re in the area that I don’t see other videos covering as much and that is: Why is it that sometimes when someone has a low compression engine, and they fill up with high octane does the
engine run better? and while there are a lot of automotive “improvements” that can be chalked up to the placebo effect, This might not actually be one of them! You’ve probably seen these fuel system cleaners anywhere that automotive products are sold. The idea behind them is that they can clean up carbon deposits that build up in the engine over time. One of the noteworthy places that carbon builds up is the combustion chamber and the size of the compression chamber compared to the size of that, plus how far the piston comes down, decides what your compression ratio is. There are actually two ways that carbon in the combustion chamber can cause high octane fuel to work better in the engine. One way is just by gradually building up and filling the combustion chamber so when the piston is at the top dead center there’s less space in the combustion chamber and that artificially creates a higher compression engine. We already know that higher octane fuels work better in high compression engines! The other way that carbon can build up and cause problems for lower octane fuel, is if it builds up in one specific spot and creates a hot spot on your piston or somewhere in the combustion chamber. That hot spot can ignite the fuel before the spark plug does, but it’s harder to do that with a higher octane fuel so a higher octane fuel in that situation would perform better. So, that being said it means you can actually use high octane fuel to diagnose these issues, If you have an engine that calls for low octane, but you’re running high octane and it runs better with it, then you know that there’s a problem you can actually take steps to fix that, and go back to running low octane. And that’s why something like this octane booster commonly has stuff in it that it’s supposed to clean the fuel system out. Even if this does boost the octane a little bit somehow the main thing that’s happening when you pour one of these in is that it’s cleaning out all that carbon buildup, and making it so you don’t have to run high octane anymore. So, if you’ve been driving a car that only needs a low octane and you’ve been running high octane to alleviate some issues, I’d recommend putting some fuel system cleaner in trying to knock that carbon out and if you’re successful in that, you’ll be able to run low octane again! But, obviously if you have a high compression engine and it requires a higher octane, stick with that. Hopefully that makes going to the gas station just a little bit easier. Thanks for watching,
I’ll see you in the next video!