Premium vs Regular Gas

I am researching cars to buy and am curious if it is necessary to use premium gas as stated by the car manufacturers? If regular gas is used all the time instead of premium will it damage the engine?

The use of premium recommendations comes in two flavors.

  • Premium fuel required

    In this case you use premium all the time (except maybe in the mountains) because if you don’t you can do some expensive damage to the engine.

  • Premium fuel is recommended.

    In this case you do not need to use premium and you will not damage the engine, but it will mean you will loose some power from the engine and you likely will loose some mileage so it might cost you more in the long run.

The answer above is correct. Most engines in today’s cars have a “knock sensor”. This device tells the cars computer when a knock occurs due to low octane fuel. The computer retards the ignition timing to the point where the knocks won’t happen.

I had a 2000 Saab 9-3 as a company car and the company allowed only regular gas be purchased. This was a “premium recommended” car and it ran fine with no issues in the 60K miles I drove it.

Currently I have a '04 Ford T’bird that is a “premium required” car and it gets premium. I’m not going to mess up a motor to save a little money on gas.

You have to check the language in your cars owners manual(s) then follow that advice to avoid damage to the engine.

If this is a concern to you than I’d suggest simply selecting amoung the wide range of choices that recommend regular. None of us knows what direction gas prices will go, but my guess is they’ll go UP!

There is only 5 octane points between regular and premium, 87-92…That is not enough to change the course of history or damage an engine. Most “premium fuel only” cars will run just FINE on regular. A few might “ping” or “rattle” a little under hard acceleration but that can be controlled by simply lifting your right foot a little. As far as damage is concerned, I have never seen an unleaded fuel engine suffer physical damage because the owner used regular instead of premium.

Back in the days when regular was 90 octane and premium was 100 or more, yes, you could indeed damage your Olds Rocket 88 with 10.8 to 1 compression by using regular fuel. But before that damage occurred (usually holes punched through the tops of pistons) the racket, the spark-knock, could be heard a block away.

In your research, check the listed compression ratio of the engines your are considering. 9.0 to 1 will run fine on regular 9.2 to 1 usually will. Some 9.5 to 1 can be coaxed to run on regular. Above that, you are going to hear a little ping under acceleration, but not DESTRUCTIVE detonation. I don’t think you will find ANY modern engines claiming 10 to 1 compression because the 92 octane “premium” fuel will not support it.

In the 1960’s, gasoline was produced anywhere from 80 to 140 octane. Gasoline engines were produced to utilize those fuels, 8.5 to 1 all the way to 13.5 to 1 compression in high performance aircraft engines. So calling 92 octane unleaded automotive fuel “High Octane” is kind of a joke and paying .30 cents extra for it is even MORE of a joke…

For 2009 the BMW M5 12.0 comp. ratio, preminum recommended (500hp) and the Cadillac CTS-V 9.0 ratio, preminum recommended (supercharged 556hp) what is odd is that preminum is not “required” in either. I really think Motor Trend is in error when they don’t say "preminum required’ but those are the published specs.

No 12 to 1 compression engine is going to survive running on 92 octane gasoline…“Published figures”, especially those published in rags like Motor Trend are highly suspect. I doubt the horsepower numbers and the 12 to 1 compression are correct. Caddy’s 9 to 1 figure probably IS correct and tends to support my argument.

Automotive magazines LOVE to “Test” very limited production cars, probably only a few hundred produced, to give wet dreams to enthusiasts who must be satisfied reading magazines…By the time the magazine hits the streets, potential buyers discover the car is no longer in production.

2010 Camaro 11.3 comp ratio 304hp (V-6!) recommended fuel unleaded regular.2010 Hyundai Genisis 3.8 comp ratio 10.4, 306hp fuel recommended regular. These cars along with the BMW M5 are production cars.

I doubt the horsepower numbers and the 12 to 1 compression are correct.

12:1 according to

Caddy’s 9 to 1 figure probably IS correct and tends to support my argument.
9.1:1 according to Cadillac’s website.

BMW can publish any numbers they want to…The only way to tell for sure is to cc the combustion chambers.

But we come back around to the fact that no matter what the published figure is, it can be no higher than what 92 octane will support. And 92 octane will only support 9.5 to one and 87 octane will support 9.1 to 1 12:1 compression engines require 110 octane gasoline to avoid detonation.

Carmakers have been publishing bogus horsepower figures since the first marketing department was put on the payroll…

The Caddys HP is SAE certified and the cars a within a hair in performance and weight.It stands to reason the HP is there. 600+HP in 2011 for the M5. BMW’s HP also is SAE certified,I checked.

With the advent of direct fuel injection, 12:1 compression is possible with 91 octane. In some cases even DI engines with forced induction can run happily on 87 octane fuel GM’s 2.0L turbo Ecotech engine is a prime example of this.

The CTS-V Caddy has a supercharged LSA OHV V8. So it has a lofty compression ratio for a forced induction car anyway, so premium is recommended.

How many M5’s and CTS-V’s have been SOLD in 2008-2009?

It would seem that with direct injection, octane becomes much less important as long as auto-ignition can be avoided or controlled…The old octane / compression ratio relationship was developed for carbureted engines. It will be interesting to see if enough consumers feel 600 horsepower cars are worth the $75K-$100K price this technology demands…

Today’s service facilities can hardly keep Subaru’s operating properly. Dealing with a CEL on an M5 will be quite a challenge.

Direct injection and the use of multiple fuel bursts combined with the heat absorbition properties of the injected fuel allows the use of compression ratios in the 10 or 11:1 range (or even higher) without the need for higher octane fuel. Good article on direct injection in this months Motor magazine

Stuff we do not even know happened…did.

Used to be, you could safely use regular gas as long as the engine didn’t ping…if you drove gently.

But today…

The computers used are so much more sophisticated than even a year ago, that you simply can not play that game.

Besides, the computer will give the best possible performance and economy if you follow directions.

Is there a “premium” (pun intended) on writing crypticaly? Shatto you can come out and state your position clearly,it advances the dialogue.

The directions are preminum recommended but not required.

So lets get back to the absent OP’s question: If you buy a 10 year old Lexus (or whatever) with 140K on it and you pay $3500 for it and you pull into Johnny’s U-Pump-It, which nozzle are you going to grab? The $2.43 nozzle or the $2.72 nozzle?

I bet that Lexus runs FINE on $2.43 gasoline and it better, because from now on, that’s what it’s going to get…

If the OE is recommending premium gas, why use anything other?

The person who started this thread 8 years ago only posted one time and I think they would have made a decision by now.

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