Longest New Car Life with High Octane Fuel?

My husband insists that my 2010 Honda Civic will have a longer engine life if I use the highest octane gasoline available rather than the lower octane the users manual recommends. This is a car we hope to keep for 200,000+ miles and probably 20 years. Hard to argue with him as with using only high test he’s gotten over 200,000 miles out of every engine he’s owned (Chevy, Toyota, Subaru). He’s an engineer so I need hard data, facts and details.

I’ve found studies from fuel companies that recommend using the higher octane for better engine life. (No surprise there, they stand to profit from that.) I’ve found studies from car manufacturers that say there’s no point to using higher octane fuel. (No surprise there, they’d like me to buy a new car sooner). Whom do I believe?

As with any car, read your owner’s manual and use the recommended fuel. Using fuel with higher octane than recommended is a waste of money.


I know he’ll never believe this, but there is absolutely NO benefit from using gasoline with a higher octane content than specified in the owner’s manual. It’s a waste of money. The engine will not last any longer with 91 octane than it will with 87 octane.

It’s not really difficult to get 200K miles out of a car these days. All you have to do is follow the maintenance schedule and fix anything that breaks.

I wish I had the money your husband has been throwing away all these years.

I agree, I can think of no possible benefit regarding engine life for hight octane gas, if it’s not recommended for your car. And I know of no studies that say that - what are the fuel company studies you’re referring to?

Agree with 3 previous posts. The owner’s manual specifies what octane gas is needed. Buying anything “hotter” is a complete waste of money.

It is the engine design that determines the type of gas to be used, not an advertising pitch or your husband’s non-technical muses about “hotter is better”.

To get really down to earth, if you don’t need Viagra, why buy it?

Higher octane fuel is used to prevent early detonation in high compression engines. Your Honda Civic does not use this type of engine. Internal combustion engines compress the gas/air mixture, then at just the right time the spark plug causes an explosion that pushes the piston down, providing power to the drive shaft and eventually the wheels. If you use lower octane gas in a high compression engine, the compression itself may cause detonation before the spark plug would. But in a low compression engine, there is no early detonation and the spark plug does it’s job. Since the engine functions the way it should, high test is a waste of money in a low compression engine.

It’s Probably Going To Cost You An Extra $600 Or More. How Much Longer Life Is He Talking ? I’ve Gotten Well Over 200,000 Miles Out Of Every Dodge, Chevy, And Pontiac I’ve Owned.

What has always killed my cars is rust and age, not engine problems or low octane gasoline.

Can you find out from him specifically what he thinks the increase in octane is going to do ? We actually need this information as the basis of an informed discussion.

Ask him what he thinks of “Top Tier” gasoline that is recommended by many manufacturers. I usually go to Shell stations for whatever that’s worth.


I bought an '03 Honda Civic new with the same idea as yours, keep it for 20+ years. I use regular gas only. I believe the car with last just as long with regular and that premium is a waste of money.

Your husband believes otherwise and I don’t think my opinion or anyone else’s will convince him. Just let him fill the car with premium. When you go for gas you can cheat and use regular; he’ll never know the difference. Save the extra money and take yourselves out for nice movie and a dinner some night.

Best answer.

The only way I could see a relationship between paying the extra money for premium and extending the life of a car…is as an indicator that the owner is also more willing to spend what’s needed to properly maintain his car and run it through a car wash more often . Then I guess you could say it “helps” ?

The best way to extend the life of your car is to follow the service manual and keep getting the full service work done even after the warranty is run out. Also dont drive like a maniac, and keep the cell phone in your pocket when you are driving.

I’ve gotten well over 200,000 miles out of plenty of cars, using regular gas and the cheapest oil ond filter on the shelf. Plenty of other folks on this board have done the same, so we can definitely put that bit of anecdotal evidence to rest.

As for these studies from the fuel companies, I’d like to see them. I seriously doubt there are any studies out there, even performed by fuel company hacks, that say that higher octane fuel will increase engine life on a car that does not require or recommend premium.

This used to be a very contentious issue, since the fuel companies did indeed used to advertise that their premium fuels were better for any car, which was actually sometimes true because they would only put the good detergent packages in the premium fuel. But the FTC made them stop both practices years ago, precisely because there is not a shred of evidence that running premium fuel in a car that only calls for regular is beneficial in any way.

But who knows. Maybe now that Exxon-Mobil is no longer denying climate change, maybe they found another project for their hack scientists to work on.

An engineer, eh? No wonder he’s being difficult. Okay, here’s a more technical description.

As the pistons in the cylinder compress the fuel mix, the mix heats up. All matter heats up when compressed. In engines that have high compression pressures, whether the cause is the compression ratio of the engine OR the pressures are boosted by a supercherger or turbocharger, the fuel can heat to a point that it self-ignites, before the spark plug fires. That create a huge pressure wave from the explosion before the rising piston reaches the top of its stroke. That shock to the upcoming piston can be devastating. It can also create a lesser version of preignition called pinging, which is a second wavefront self-igniting and crashing into the spark-induced wavefront. Again, that can be devestating.

Octane is actually a measurement of gasoline’s resistance to detonation. The higher the octane, the higher the resistance. In engines with high compression pressures high octane gas is used to prevent the aforementioned preignition.

Properly operating engines that do not have high compression pressure in the cylinders, like most Civics (read your owner’s manusl), do not need the detonation inhibitors. The cylinders do not reach high enough temperatures to self-ignite.

Show him this. Then take him to a nice place for dinner. If he still insists, then use high test. Harmony is bliss.

I’ll give your husband this: it used to be that some high octane gas had more detergents than ‘regular’, resulting in a cleaner fuel system. I don’t think that’s the case any more, as shown by Shell and the ‘Top Tier’ gas group putting pretty much the same detergents in all grades.

See my earlier post-- it’s illegal for them to put different detergents in different grades now.

IMHO, the practice you see nowadays of some stations having ethanol-free premium (but ethanol-containing regular and midgrade) is pretty sleazy.

Octane is a measure of how fast the fuel burns. Too fast and it can damage the engine. Higher octane burns slower. Higher than what is needed, will not do anything to or for your car.

Octane does not measure additives, power, cleaning ability etc.

Diesel cars like mine measure the same thing using a cetane where higher burns faster.

If you want long life, get that owner’s manual out and do what it says.

Back in the 60’s high power cars called for high octane. That is not normally the case today. The car makers have found other ways of gaining power.

The only engine I ever destroyed ran out of oil.

Chances are, the second owner (or third) of your Civic will have it towed to the salvage yard when the TRANSMISSION fails or the timing belt breaks…High octane fuel won’t help at all…

You’d be better served by using the recommended octane and spending the extra money if you want on putting a can of injector cleaner in it once in a while, and using synthetic oil at oil changes.

at 25 MPG, and a $ 0.20 price differential for premium, it will cost $1600.00 over 200,000 miles. Absolutley insane. Follow the mfg recs.