Is there any difference between different grades of gasoline, other than the higher grade being “cleaner”?
Here’s why I ask: My car (2000 Subaru Legacy) owner’s manual (yep, I actually read it) says to use 87 grade or better. Since I love my car, I put the 93 in all the time, I figure it’s better for the engine and will help it last longer. Now my check engine light comes on periodically, but never stays on for more than a day, and there’s nothing wrong with the engine (dealer checked it out). Could it be that I’m using different gas then was recommended? Is there something about the 93 grade that would make the sensors or whatever think their was something wrong with the engine (I’ve heard it has something to do with the gas/air mixture)?
Well as far as I know it doesn’t really matter if you put the 87 or the 93 in your car. It shouldn’t make any difference. 93 is just a high octane fuel.
Higher octane (that’s what the 87, 89, 93 rating is) basically gives you more bang for a given amount of the fuel. Thus, your engine doesn’t have to work as hard with higher octane fuel since a single stroke of the piston will deliver more power than with a lower octane fuel. Also as a result your car should get better gas mileage with higher octane fuel.
Is it worth it? I dunno. I’ve never done a cost benefit analysis to see if the extra price for the gas is worth it or not. My gut reaction is you probably pay slightly more for the higher octane stuff than you save in better performance (this does not include maintenance costs from an engine that wears out sooner).
Also a WAG is that I doubt your car will last in any significant way longer with ‘cheap’ stuff than with the ‘expensive’ stuff. So many things can go wrong with a car that the saving on engine wear and tear with higher octane fuel is probably somewhat negligible.
FWIW I have heard that the 93 octane fuel is a waste on most vehicles. A few models (Corvette, Porsche and some others) recommend the 93 octane fuel. Besides those however I think you’re better of with the 89 octane fuel. Engines are designed to run effieciently with certain fuels and your just not getting your money’s worth on 93 fuel in a Subaru. Jet fuel is way up there in octane (120?) but you wouldn’t want to put it in your car.
So I’d say back off to 89 octane fuel and save a few bucks.
Sorry Jeff_42 but your description is a common myth and is mostly wrong.
Octane is a measure of gasoline resistence to detonation. What it actually means, is that the higher the octane the LESS energy. This is because the bonds are tighter, and it takes more energy to overcome those bonds and get gasoline to combust.
Engineers can use this property to design engines that produce more power. But the key is, the engine must be designed for this, otherwise higher octane will do you no good and can in fact do you some harm. Your Subaru engine is not a high compression engine.
The way an engine can get more power from high octane is to increase the compression. That way they can get more gas and oxygen in each stroke under higher compression. But you need high octane gas to prevent it from combusting too early, before the spark plug fires. If you are using high octane gas in a car designed for low octane, the gas/air mix can burn later than it’s designed for, causing the still burning mix to enter the exhaust system.
So, buy what the owners manual says. Do not buy a higher grade unless your car knocks and pings (premature detonations). Any higher grade gas you buy is a pure waste of money and will have no benefit in MPG or engine performance.
I’ll go with Telemark and Jeff on this one. A few years ago, I watched a program on T.V. dealing with this matter, among others. Specialists were pretty unanimous in saying that the highest octane is a waste of money. On the other hand, I’ve had pinging problems with my previous car (VW Passat), switched from the 87 to the 89, and the problem stopped.
Sorry Jeff_42, I reread what I wrote and I came off a little harsh on you in that first sentence. The myth I was refering to is the fact that higher octane gas has more energy than low octane. The truth is the reverse. Your last paragraph is pretty accurate.
Also, from what I’ve read and determined, you don’t necessarily need to use as high an octane rating as is recommended in your manual. You just need to use a high enough octane that doesn’t cause the engine to ping. My '93 Volvo’s recommends using at least 89 octane. I spoke with Volvo customer service and they said that 87 wouldn’t do the car any harm, but I might see reduced power and/or mileage. Having done the comparison (yes, with several tanks of gas), I haven’t seen any difference in either. With modern computerized engines, pinging is pretty much unheard of.
One car I looked at (possibly the current Nissan Maxima; don’t remember) gives a 5 HP difference between 87 and 89 octane (or was it 91?). At any rate, most likely not worth the extra $$.
This question comes up to the guys at Car Talk every now and then - here is one of their latest replies.
It basically agrees with what people are saying here: higher octane only increases knock resistance, and is a complete waste unless the car is designed for it.
Personally, my 1989 Escort pinged (pang? :)) unless I put in mid-grade. I’m pretty sure that it wasn’t designed for it, but the difference was noticeable. Engine deterioration, perhaps?
The only thing I put premium gas in is my 5 HP push mower. It seems to me there’s a noticeable difference in power–gone are the times when it stalled in high grass. My dad and grandfather also use premium in their small engines and find they run better. (YMMV)
Should I conclude that small engines have higher compression ratios?