I can buy super unleaded gas here in South Carolina for $2.69, and I was wondering if anybody has used high grade fuel?

-Will it help my MPG?

-Will it hurt my car to go back to regular unleaded when gas prices go up?

I still have half a tank to go, so gas prices could change by then, but just curious

 

Excessively high octane is a waste, and you'll see no mpg improvement for using it. Octane is a measure of the gasoline's resistance to premature detonation (aka knocking/pinging), and higher numbers are needed for high compression performance engines. Ours aren't, so unless there's a specific reason to get some (like it's cheaper than regular, or it's all the station has left), save your money.

Also, you can often search for older threads (like https://www.greenhybrid.com/discuss/...eage.9376.html) for similar info.

 

Check other threads on this issue. Using a higher octane level than your owner's manual recommends is a total waste of money. It won't help your FE at all, and may over time damage the engine.

 

I say go for it. Don't believe anybody here if they say it's not worth the extra expense. You will see up to 5 mpg difference without trying.

 

The owner's manual states that you should use "unleaded gasoline, pump octane number of 87 or higher."

While I personally would not pay for higher octane gasoline, it does not appear that it is harmful to the vehicle.

 

My dealer specifically told me not to put higher than 87 in the vehicle. He said it would hurt more than it helped.

 

I have experimented with High Octane in my Honda Civic hybrid a few times and here is what I have noticed. When I run regular unleaded and drive as careful as I can I get about 44-47 MPG. When I use super unleaded I average about 54 MPG. This morning on a ride in to work (30 miles) I averaged 61 MPG. I never got this type of FE with regular unleaded even when I drove as careful as I could. Not sure if the cooler weather helps too. I will keep experimenting. Anybody else notice this?

 

I am using RON 99 (around MON 87.5), whenever I can find it. There are lots of posts in this forum quite consistently arguing this is plain stupid, so I won't try to turn that around. I can only recommend people to look for this information in completely other forums (fora?). Don't stop looking until you find a more elaborate explanation of how the combustion process works, with the different intermediate steps of combustion of the fuel and oxygen, how the combustion front progresses through the combustion chamber, what triggers knocking, how the knocking detection module in the control unit works (yes, it's a separate module, since it requires some computing power), and control strategies to prevent and protect against knocking. Then draw your own conclusion. I have.

People saying it will hurt the engine should provide some supporting detail on more exactly how that would happen. There must be some physical explanation, right? Since so many seem to agree, it shouldn't be too difficult to understand, or? I'd love to hear more about it. Then explain this to the Honda engine designer who recently claimed the V6 produces 10 hp more on super than on regular. (Could have been Toyota. There is a thread about it in this forum anyway.)

 

The main benefit of higher grades / octane is the change of the combustion point... in other words, resistance to detonation. This is only important in high compression (> 10 to 1) engines. Knocking (pre-detonation) can occur using lower octane fuel in high compression engines. This can cause engine damage.

Doing the reverse (high octane fuel in low compression engines) will only hurt in one place... the wallet. I've never heard of or seen damage caused by using too high an octane fuel. It's just wasteful, that's all.

Even if there were some other mystery benefit to using high octane fuel which gave 10% better economy, the increase in MPG wouldn't likely justify the higher price of the fuel.

Lastly, please ponder this....

Auto manufacturers will do anything to increase their EPA mileage ratings. They need to to achieve CAFE standards (corporate average fuel economy)... and compete with everyone else. If it was as easy as requiring 91 octane fuel to get a 10% bump, wouldn't every manufacturer do it? Of course they would! Same goes for those aftermarket air filters, nitrogen in the tires, tornado air intake blades, and every one of the snake oil potions that have been fraudulently sold since cars have been one the road. They just don't work. They may have other side benefits... but improved MPG is not among them.

 

Jeff, I could not have said it better myself.

Just to add a little more to what may already be common knowledge: Much testing has been done to determine if higher octane fuels delivers a statistically significant improvement in fuel economy for today's engines. The results seem to consistently show that it does not. In the end, for most people it is literally a waste of money.

Now, there have been cases that some higher end (high octane) gas brands may include additives that are not present in the lower grades of their gas. These "may improve" the engine's operation and hence have a smaller positive impact on performance and fuel economy.
This phenomenon however, has only been observed in higher milleage and/or poorly maintained engines. For our cars' engines, the more academic consensus is that even these additives will do very little or nothing to optimize an already well tuned setup.


Cheers;


MSantos