# Can higher octane gas cause engine noise?



## jw (Dec 21, 2001)

OK... been putting super unleaded in all my cars since I can remember. Last month the 3.6L CTS I picked up states in the manual that it is designed to run on 87 octane. Regardless, I've still be putting 93 octane in it. I've been noticing a few rattles when I first start the car at idle. I was going to have it looked at during my first service. However, I'm reading from folks on cadillacforums.com that this is caused from putting higher octane in the engine. The 3.2L CTS was designed for Super and the 3.6L CTS is Regular.

Can this be true?



caddieboy said:


> Quote:
> 
> 
> > Originally Posted by j-w
> ...





tzoid said:


> this is an old thread that has had lots of info provided on grades of gas for the '04 CTS with the 3.6L engine, many by the General's factory technocrats . Long story short...designed for 87 octane, will not provide ANY additional hp from higher grades, can potentially do more harm than good due to detonation points of higher grades and last, but not least, a waste of money. You should be thrilled that the 3.6L was designed this way...prestigue no longer exists because it burns high test!


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## AF (Dec 21, 2001)

I was always under the impression that higher octane can only help the car run better :dunno: 


Did you ever find an answer to this ?


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## Nick325xiT 5spd (Dec 24, 2001)

higher octane gas requires more energy to ignite. If an engine isn't set up for that, you end up with unburned fuel. Generally not a great thing.


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## jw (Dec 21, 2001)

AF-RX8 said:


> I was always under the impression that higher octane can only help the car run better :dunno:
> 
> Did you ever find an answer to this ?


I was under the same impression. The discussion goes back and forth. Closer reading of the later model year manual states:


> Gasoline Octane:
> 
> If your vehicle has the 3.6L V6 engine, use regular unleaded gasoline with a posted octane of 87 or higher.* However, for best performance and for trailer towing, you may wish to use middle grade or premium unleaded gasoline.* If the octane is less than 87, you may get a heavy knocking noise when you drive. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you might damage your engine.
> 
> ...


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## The Roadstergal (Sep 7, 2002)

You're wasting your money if it doesn't need 93 anyway.

Your car will only run better on higher octane up to the point where it no longer engages the knock sensor. Of course, you'd need diagnostics to know when that happens. F***ing overengineered hands-off cars.


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## swchang (Oct 5, 2003)

For cars that require only 87, I've heard it's a good idea to fill with 93 about once a month.


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## The Roadstergal (Sep 7, 2002)

For the additives, probably. There's no other reason I can think of in a car that's happy on 87. I use Redline fuel injector cleaner instead - 10 treatments for $4.


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## jw (Dec 21, 2001)

The Roadstergal said:


> For the additives, probably. There's no other reason I can think of in a car that's happy on 87. I use Redline fuel injector cleaner instead - 10 treatments for $4.


 best performance and for trailer towing ?


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## Pinecone (Apr 3, 2002)

Octane ONE MORE TIME.

Higher octane means a higher resistance to detonation, ONLY. Not harder to ignite, not slower burning, not more power, just resists detonation.

As RoadsterGal points out, higher octane can give more power up to the point where the engine system is running at the maximum capability based on allowable ignition timing, cam timing, compression ratio etc. In an E46 M3 under standard conditions, that seems to be about 96 AKI according to tests I have seen. Other cars will respond more or less well.

Under non-standard conditions (higher air pressure, higher temperature) the knock sensor may be retarding timing and other engine parameters to stop detonation. In this case haveing a higher octane than required may allow the engine to produce full power when otherwise it would be reducing output to protect the engine. No way for you driving along to tell this is happening or not. But if maximum performance is that important, running higher octane helps.

Premium fuels contain more and better additives. I have found in informal testing that a tank of Mobil 1 Super Premium will increase the gas mileage in our 90 Jeep Cherokee by 1.5 - 2 MPG for a failry long period of time after going back to regular.

So, bottom line, if hte car is designed to run on regular, save the moeny and run regular, with an occasional fill up of high quality premium, or run an occasional fuel system cleaner through it. But running higher octane hurts nothing other than your wallet.

It does not cause noises from the engine.


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## swchang (Oct 5, 2003)

Pinecone said:


> Octane ONE MORE TIME.
> 
> Higher octane means a higher resistance to detonation, ONLY. Not harder to ignite, not slower burning, not more power, just resists detonation.
> 
> ...


Any benefit in running a fuel system cleaner on the 3ers? Every 5000 miles, or any other suggested intervals?


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## Pinecone (Apr 3, 2002)

BMW recommends occasional use. In the Z3s there have been problems with fuel sneders going out, I don't hang on the 3 series boards.

I run a bottle of BMW fuel cleaner through the M3 every 2 K miles (easy to remember). On the Roadster I run some RedLine SL-1 and some water remover most every tank. And both run high quality fuels normally, but I do make a point of filling up with Mobil every so often.


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## swchang (Oct 5, 2003)

Pinecone said:


> BMW recommends occasional use. In the Z3s there have been problems with fuel sneders going out, I don't hang on the 3 series boards.
> 
> I run a bottle of BMW fuel cleaner through the M3 every 2 K miles (easy to remember). On the Roadster I run some RedLine SL-1 and some water remover most every tank. And both run high quality fuels normally, but I do make a point of filling up with Mobil every so often.


Why not just use the same cleaner on both? Is there a major difference in all the different cleaners out there? I was thinking of going to Advance Auto Part or Costco and picking up the cheapest I could find. Would you suggest the BMW one instead?


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## Pinecone (Apr 3, 2002)

No real reason. I started with the Redline in the Roadster first. Then when we got the M3, I bought a case of the BMW cleaner and started that regime.

Either way will work fine.

I would use Redline, BMW, or occasionally Chevron Techron, NO others. And there have been some reports that the BMW stuff is repackaged Techron anyway.

You want it to work, but be safe for all othe other fuel system parts. The BMW stuff is pretty cheap. WIth Redline, I use like 1 - 1.5 ounces per tank, also pretty cheap.


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## swchang (Oct 5, 2003)

Pinecone said:


> No real reason. I started with the Redline in the Roadster first. Then when we got the M3, I bought a case of the BMW cleaner and started that regime.
> 
> Either way will work fine.
> 
> ...


Cool, thanks for the tips! Any idea on the part number for the BMW stuff?


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## Pinecone (Apr 3, 2002)

Not off hand. Just go to the parts counter and ask for the fuel system cleaner.


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## swchang (Oct 5, 2003)

Pinecone said:


> Not off hand. Just go to the parts counter and ask for the fuel system cleaner.


Hey Pinecone, do you remember where you got the cleaner? The guy at Russel says they don't sell it and can't order it...


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