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I'm using the Edmunds car compare tool to compare some AWD sedans for my wife - The Audi A3 is listed as "Premium Recommended" for gas type, while the Infiniti Q50 is listed as "Premium Required" for gas.
What's the difference? And, was the Infiniti dealer throwing us a line of Bull when he said that we could get away with regular unleaded? Is the Audi A3 okay with regular gas?
We also looked at the Volvo S50, BMW 320i or 328i and the Lexus IS300. Only the Volvo seems to be okay with Regular Unleaded per the specs on Edmunds.
Having test-driven all of them, I really liked the Audi A3 best and probably the Volvo the least - just based on my personal test driving experiences. (I'd probably rate the Infiniti 2nd best)
99.9% of cars the premium is a waste of money. I drove an Audi A8 for 3 years/48K miles and it never got a single drop of premium fuel and the car ran fine. Unless the car pings under acceleration or gives you some other indication of trouble just put the cheap stuff in it.
Car and Driver did a test with the fuel grades on a E46 M3. Their results were the car felt fine but lost a tiny bit of performance (like 1/10th of a second in the 0-60 times).
There are ONLY two differences in gas, the octane, and the additives.
And these do NOT directly effect the energy available in the gas. IE: the mileage.
RE: Octane:
In general, the higher the temperature a gasoline engine can operate, the more efficient it is, (the better mileage).
The higher the octane levels, the hotter a car 'can' run, without knocking, IF its so designed to take advantage of running at these higher temperatures.
Standard engines are designed to run at standard temperatures. They are computer controlled with sensors etc, and typically 'can' run with any type of gas by self adjusting, (as it has been noted above). They won't (or can't) operate at the higher temperatures a higher octane allows, so they self-adjust down to the standard temps, and the higher octane is 'wasted'.
Using a higher octane provides no additional benefit.
High-performance cars are designed to normally run at a higher temperature. So a higher octane gas allows the car to self-adjust and run at the higher temp, (with the high-octane helping the car to minimize knocking). A slightly higher efficiency means a slightly higher mileage.
I know some cars that call for higher octane can still run with lower octane, and will do so by the motor detecting this, and self-adjusting down to the lower temps, (and lower inefficiencies). As another poster said, some cars that 'need' high-octane are designed to run at the higher level and will show a markedly reduced performance when operating on low-O gas.
The idea is that the few dollars more you pay for the higher grades of gas, will also get you slightly better mileage. It's tough to say if the boost is actually worth it, so you should run a few tanks of regular, and then a few with higher octane, and keep track of mileage vs costs.
FYI: The other difference in the gas you can get: RE: gasoline additives.
Basic gasoline is regulated by law and is the same, (Disregarding octane levels). It is stored and distributed to the different gas station chains, who then mix in their own additives (detergents, etc).
I've been on a test drive that required a fuel up on a car that required premium and they just put regular in even after I mentioned it. "It will be fine".
Like, you're going to trust a salesman who makes a living BSing people? D'ya really think he knows more about the mechanics and technical requirements of the motor than the manufacturer does?
If the manufacturer says "Use premium", then use premium. There is a reason- the motor is designed to run on that fuel, and it will not run as designed if you do not.
If it detects detonation from running lower octane gas, it changes fuel/timing curves to reduce/eliminate the knock. As a result you may lose HP/fuel economy.
Also, you are relying on the sensor to "save" your engine, as detonation can cause major damage. Personally, I feel that if the manual says to run 91+ all the time, then that's what you should do. Fuel costs should be a factor in your decision to purchase a car and you should take into account the requirement of running premium fuel.
If you want to take the risk and save 20 cents a gallon, here's the potential damage that can occur from detonation. That's a lot of faith to put into a knock sensor to prevent this
It is compression, not temperature that determines whether you need high octane. Regular gas when compressed in a high compression engine will explode prematurely. Pre-ignition results in an incomplete ro dirty burn. Premium gas has more ethanol (usually) or other additives which make it less explosive and therefore can be compressed more without exploding.
There are a lot of misconceptions about high octane gasoline. Some people think it burns hotter or cleaner (does not, in fact it has slightly less energy in it). Some people think it will improve their MPG in a vehicle with normal compression levels (it will not, it will just waste your money). Some people think it can help to "clean out" a normal compression engine that is running badly. (wasting money once again, usually has the same detergents as regular gasoline). High octane does one thing and one thing only. It it does not explode or pre-ignite during the compression cycle before the engine is fully cycled. If you do not have a high compression engine, it does not do anything for your vehicle. Nothing.
"But i tried it and i get better MPG with premium" No you don't. Not unless you have a high compression engine. You are imagining it or simply mis-measuring.
"But my regular compression engine car runs better on premium I can hear it. " Psychology. You believe it, so you hear what is not there.
The reality is for most cars even many with premium recommended, it is a waste of moeny and does nothing, or so little you will never notice it. Most modern cars adjust for lower octane and if they are high compression you may see a tiny drop in HP or MPG, but probably not enough you will be able to discern the difference. On the other hand, if you get preignition (pinging) you need to stop driving asap and get higher octane fuel or an additive. Preignition can burn up your valves.
BTW a friend who owns a gas station told me the delivery trucks frequently bring high octane fuels and just put it in all the tanks. The octane ratings are a minimum. Thus, they can sell 91 octane as 87 because it is at least 87. My understanding is they do that at times because it is cheaper to just make one delivery than to ship in different fuel mixes. He said they do not do that all the time, but at times when you buy 87 octane, you are really buying 90 or 91. I had a high compression engine (premium only) and he would tell me when they had premium in the regular tanks, so I could save a few dollars (plus it guaranteed I would buy all my gasoline from him). That car would almost always ping on regular gasoline, but not on the regular that was really premium. I once had to fill up with Pemex gasoline in Mexico and they did not offer premium. I expected problems, but had none. Maybe their regular gas is also premium, not sure.
The middle grade gasoline is really silly. It is a sales ploy. Many people who are uncertain whether they need to spend the extra money for anything "premium" will just choose something in the middle. Very few cars (none that i am aware of) require only 89 octane. They are either fine at 87 or they require 90 or 91. Thus, 89 is either too low for your car or a complete waste of money. Maybe there are some mid level engines, but I doubt the gasoline you are getting out of the 89 octane pump is any different than what you get out of the 87 octane pump.
Like, you're going to trust a salesman who makes a living BSing people? D'ya really think he knows more about the mechanics and technical requirements of the motor than the manufacturer does?
If the manufacturer says "Use premium", then use premium. There is a reason- the motor is designed to run on that fuel, and it will not run as designed if you do not.
Oh, no you misinterpret me. I would always use premium for a car that required it. I'm just saying that the sales folks won't and would rather let it run poorly than have the cost of premium eat into their bottom line.
Like, you're going to trust a salesman who makes a living BSing people? D'ya really think he knows more about the mechanics and technical requirements of the motor than the manufacturer does?
If the manufacturer says "Use premium", then use premium. There is a reason- the motor is designed to run on that fuel, and it will not run as designed if you do not.
well, the Infiniti is listed as Premium Required online, but the sales guy said it would run fine with regular unleaded.
The Audi was only Premium Recommended, but the sales guy said you must use 91 Octane or higher.
Of course, I'm not one to judge who knows the most about cars, but the guy at the Audi dealer did seem to have a pretty good handle on the cars for sale there.
That post exceeds half ....it was a full on informative and factual post.
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