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Can I add Xylol (Xylene) to boost octane?

A recent question about octane and a visit to a paint store made me wonder:

Can I add Xylene to my gas tank to boost octane? My car calls for 89 or better octane, but I can usually get away with using 89 every second or third fill-up without getting noticeable spark knock. On the rare occasions I’ve filled with Sunoco 93 octane fuel, I can smell xylol as I’m filling my car. I know that it is one of many additives that boost octane. (by making gasoline burn somewhat slower)

Can I add pure xylene to my tank to boost octane? Do you think it would harm a catalytic converter or oxygen sensors? What would be the recommended percent to add to increase octane a couple of points?

Anyone with some knowledge of chemistry have any input?

Yes, you can. You’ve discovered the secret to boosting octane. You sly bastard! The government will soon be sending someone to pick you up. You will likely be tortured at Gitmo, or perhaps somewhere in the middle east. Egypt?

Sorry, we don’t torture. My mistake.

Be that as it may. If the government doesn’t pick you up the oil companies will, and they’re WORSE. I’m glad I’m not you, oblivion. I wish you the best of luck. I suggest running NOW, before they get your location.

Too late, they already have it.

You have opened a very dangerous can of worms. They will be looking for you. They will find you. You can’t hide. You have exposed the Xylol (Xylene) conspiracy. God help you.


You’re a cheapskate. If your vehicle needs 89 or better then you should feed it 89 or better.

There are no products that will make up the difference.

Xylene may damage the polymer products it comes in contact with. I’d be very careful with it. It severely attacks virtually any elastic product, such as nitrile, latex, silicone, and urethane. Gotta rubber hose? It’s gone if you use xylene, and how will the dissolved rubber affect your other components?

lol… actually I’m not a cheapskate. I feed it what it needs. But if the oil companies actually add xylene as an additive to boost the octane, then sell it at a 20? premium per gallon, why shouldn’t I buy a can of pure xylene and do the same? It’s no worse than folks with diesel cars using old fryer oil in their tanks to save money. If I add an aftermarket octane booster and my spark knock goes away, it’s demonstrably proven that there are “products that will make up the difference”

Obviously, that is not the case as you said

" My car calls for 89 or better octane, but I can usually get away with using 89 every second or third fill-up without getting noticeable spark knock"

Use the fuel that your owner’s manual requires. I’m sure spending the extra $2 per fill up won’t bankrupt you.

I intend to keep using the ‘correct’ fuel for my car unless I have a reason to do otherwise, and obviously the $2 per fill up won’t bankrupt me. And as many have stated in this forum, use the lowest octane that your car will run well on, and there’s no benefit in using higher octane than this. Filling up every-other time with 89 when my car runs fine this way seems to me to be just being intelligent about it, not cheap.

However, my question was is it possible to use xylene as an octane booster, and what if any consequences should I expect. Telling me to use the fuel that the owner’s manual specifies does not answer my question. So far, jtsanders has come closest to a useful comment, no offense intended.

Ok, I’m still curious as to what everyone has to say, but after a web search, I’m not nearly the first to have thought of this. Many racers have been doing this forever to boost octane. There are various formulas for homebrew octane boosters containing xylene, toluene, and other solvents. Apparently the key is to not get too carried away and to use a lubricating agent such as Marvel mystery oil or a couple of ounces of two-cycle oil or kerosene. This supposedly will help protect rubber components and other ‘edibles’ in the fuel system. After some searching, apparently many gasolines already contain methanol, ethanol, and/or mixes of xylene, toluene, and other chemicals that are already somewhat bad for rubber and plastic components, and emission control sensors. Based on the price of xylene and the amount of octane gained, it would probably be worth doing to boost octane a little cheaper than shelling out for premium, but only slightly when you factor in the bother of mixing it. So I’ve kinda answered my own question. But I’m still interested in anyone’s viewpoint. If you’re interested, here’s the Google search:

“After some searching, apparently many gasolines already contain methanol, ethanol, and/or mixes of xylene, toluene, and other chemicals that are already somewhat bad for rubber and plastic components, and emission control sensors.”

This sounds like BS to me…Could you source these statements?

Everything comes with a price so I guess you can steal the Xylene somewhere. Maybe you can read the MSDS to check for the hazards of handling it too. Who knows? It may have drawbacks.

You want miracle gas additive? Here you go:


It’s just as good, if not better than, what you’re proposing.

Operative word here is: SCAM.

What kind of car?
Odds are if you’re suffering chronic spark knock then either the timing is advanced too much (distributor equipped engines) or the engine has an EGR system fault.

Feed it what it calls for. You can may be knocking and you might not hear it. Even if it is not knocking nor causing any “damage” to the engine, it is likely that you are loosing power and mileage, so you may be spending more for fuel than you would if you just bought what was recommended.

I would not suggest trying to mix a DIY mix for raising octane. You might save a few $$ but then you might end up causing a problem that would cost far more, not to mention all the bother when you could just buy what is needed.

Next time if you don’t want to buy premium, don’t choose a car that needs it.

I’m glad that this is just a “thought experiment” and only a matter of curiosity; and, not a serious proposal for everyone to become fuel chemists.
These various chemicals are dangerous to handle, use, and what of the products of combustion? Noxious, no?
As far as octane needs are concerned, how many Joe Six Packs can evaluate an engine run on different levels of octane? How many know that singular misfires aren’t detectable through “seat of the pants”?
Curiosity is great; but, BEWARE cat!

The engineers speced 89 octane for a reason. And generally the owner’s manual will indeed inform you of the required fuel. I have never seen a manual that doesnt.

BTW what kind of car is this? I the only engine that I know of that calls for 89 octane is the pre-2007 Chrysler Hemi. Most of othe engines call for 87 or 91.

I am an engineer rather than a chemist, so you can take my opinions with a grain of salt but:

  1. Yes xylene will raise the octane of regular grade pump gasoline. I cannot tell you what the optimum mix ratio might be, though.

  2. Moderate amounts of xylene (<5%) should have no effect on seals and other components in gasoline systems. Xylene is a naturally-occuring consituent in gasoline.

  3. I would be surprised if oil companies were currently using xylene as an octane booster. In these days of ‘reformulated gasoline’, they are trying to minimize the hazardous air pollutants (HAPs) in the product. On that note, you are probably breaking a couple of laws when you pour untaxed (no highway tax paid) poison in your fuel tank. If you were to use waste xylene (already used in some cleaning process and discarded), then you would definitely be breaking a federal law by adding it to your tank.

  4. If you are buying xylene at the hardware store, I would not expect that you would save enough, relative to the cost of higher octane fuel, to make it worthwhile. I would have to research the amount required and the cost of xylene to figure that out.

You can save some pocket change by buying 1 part 93 and 2 parts 87 when you get gas.

What you are really asking is can you formulate your own premium fuel using the cheap stuff as a base? The answer is an unqualified maybe.

If you drive 100000 miles a year and you get 20mpg average, that’s 500 gallons of gasoline a year. Assuming that you can boost the octane adequately for 10 cents a gallon and that you pay a premium of 20 cents a gallon, you’ll save .1 * 500 = $50 a year.

Of course, there is a small risk that you will overlook something and destroy the catalytic converter(s) or the O2 sensors, or the fuel pump or screw up the oil, or blow the car up. But what the heck … no guts no glory. Just remember the mottos of Darwin Award winners, “Hey everyone, Look at me” and “What could possibly go wrong?”

McP! I didn’t know you had it in you!

To the OP: sure, go ahead and experiment. Let us know how you made out. Try some canola oil in the crankcase too. It keeps my eggs from sticking to the pan in the morning even at med-high, so it should work great in the engine.

By the way, how much IS a gallon of xylene?

Guys, this WAS a thought experiment. It’s interesting how vehement opinions are regarding actually doing this. Since Xylene is about $10 a gallon can, and I’d probably have to add at least a quart each fill-up to significantly boost the octane, I’ll probably refrain from doing it, now that I know that it will work, since just getting a little higher octane gas is cheaper and easier. That said, I wish to thank those that actually responded to my question, while many just said: (to paraphrase) “that I was a cheap bastard and should just fill my car with what the manual recommended.” LOL. After some mildly exhaustive research (okay, a few web searches and some rum intake), I discover that many boy (and likely men and women too) racers have been doing this for years to increase octane, as well as using acetone, ether(s), toluene, and other compounds. (of which many are already present in the gas we all buy. (do your own web search if you have doubts as to this (-: ) Since my 10-day vacation (not nearly long enough by far) is at a close and I must return to work tomorrow, I have abandoned thoughts of cheaply creating higher-octane fuel, and will occupy my mind with the pain of having to get up at an ungodly hour and return to the grind. So thanks to all and consider this closed.