High octane gas and synthetic oil

Is there really any advantage to using high octane gas in your car or synthetic motor oil?

Incidentally, I’d like some kind of quantitative proof, not stupid answers like “Oh, I can FEEL a difference in the way the car performs” or other such marketing drivel. I know some cars specificly tell you to use them, but for those of us who drive non-performance cars, is there any advantage?

Has anyone done a study for example, where they measure extra mileage driven on higher octane gas (assuming it gives you better miles-per-gallon) versus what you pay for the stuff?

I live in California, land of high priced gas, so I’d like to know what’s a “best buy” for what you pay in the long run…

Unless you drive a high performance car, buy the cheap gas. My evidence: I drive an '87 Chevy Celebrity, which is old as the hills but still runs quite well. Until recently, my father drove an '89 Oldsmobile Somethingorother (It was essentially the same car, right down to the engine. Any auto buffs out there remember the name?) We stongly disagreed about gas. Dad sprung for the high-octane stuff, while I --being a poor student-- stayed with 87 octane. Dad’s car crapped out first :D. The moral: the way you drive the car affects the gas milage and car life alot more than the type of gas.

“I had a feeling that in Hell there would be mushrooms.” -The Secret of Monkey Island

Let me be very clear on this. Octane rating has nothing to do with engine performance. Octane rating is a measure of resistance to engine knock. Everything else being equal, a higher octane gasoline will make your engine less likely to knock, no more, no less.

Having said that, the way they achieve higher octane in gasoline nowadays (rather than in the good old days, when they just added tetraethyl lead) is to use a different distillation fraction. So everything else is not equal. But very nearly so. Buy higher octane gasoline if your engine is knocking. Otherwise, save your money.

Let me restate the main point: Octane rating, by definition is a measure of resistance to engine knock.

Ex cathedra,

“The inability of science to grasp Quality, as an object of enquiry, makes it impossible for science to provide a scale of values.”
Robert Pirsig

Pluto is right, the octane rating is a measure of how much a given air-gasoline mixture can be compressed before it expodes.
If it expoldes before the piston is near top dead center, knock occurs. However many modern engines have a way of detecting knock and automaticaly make changes in the timing or air fuel mixture to prevent it.
If you are using gasoline with an octane rating that is too low, the changes can cause your performance and gas mileage to suffer. In that case a higher octane rating would be a good thing.
Your car manual will tell you the minimum rating you should use and there is ordinarily no benefit to using a higher rating.
According to the manual, my Accord V6 VTEC engine will function properly with an 86 octane rating, but will develop a few more horsepower with higher ratings. That’s not enough of an incentive to make it worthwhile for me to spend the extra money though.

use whatever the instructions tell you to use. but don’t take my word for it, these guys are the authority on cars. (cecil consulted them about downshift vs. neutral braking)

I don’t know about gas, but Consumer Reports did an article on motor oil about five years ago. In it, they concluded synthetic oil wasn’t superior enough to justify the added cost, IIRC. You might check their web site, or look at a recent Buying Guide.

Synthetic oils do have a few advantages.

  1. They run slightly cooler. (Not a big deal if your cooling system is up to snuff)
  2. They don’t break down as quickly. (Doesn’t matter at all, they still carry impurities and must be changed @ regular intervals)
  3. They provide (slightly) better lubrication. (Whether that’s worth the added cost is a judgement call)

My advice:
Use it if you can afford it.
Don’t switch from regular to synthetic if your car has any real milage on it (60k+). Any tiny, inconsequential oil leak that your engine may have becomes a big leak w/ synthetics.
Conversely, small oil leaks in motors using synthetics can sometimes be cured (or at least repair delayed) by switching to regular oils.

The octane question is now a bit more complicated than it has classically been. Some cars have computerized injection/ignition systems that will compensate for a low-octane fuel, but won’t run as efficiently when doing so. So “Don’t use high-octane unless you’re pinging,” is no longer universally correct.

The answer, alas, is to use what the engine manufacturer says you should use. (Unless you’re pinging, in which case you definitely need to A) have the engine and/or the gasoline looked into and B) go higher in the meantime.)

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

I have a big beef about Consumer Reports test of motor oil–they used New York City taxi’s as their test vehicle. You may think it would be a good example of accelerated wear in that the taxis are used heavily throughout the day, but they miss a key point: the parts of an engine wear more when an engine is started when its cold than at any other time. Taxis are virtually never shut off and when they are, they’re rarely left until they’re cold.

I drive like mad, and I’ve pushed my little Civic much beyond its “normal operation” design considerations, so I use synthetic oil (really a misnomer–it’s just more refined from what I understand). The promise of synthetic oils is they resist thermal breakdown, and since I run the car particularly hot, I use them. (Note that the average oil temperature may not be too bad but right near the cylinders it’s cooking pretty good).

I use the higher grade gas because it feels like the car is faster, so I’ll stop there (I deleted a whole bogo-paragraph about it.)

Hey, aren’t you supposed to be at work?