jump to example.com

Seeing Michael Waltrip’s sad-sack face on the front page of CNN and reading the associated story from a couple of angles got me to thinking about how little most people know about fuel additives — and how much BS I’ve heard about ’em.  I suppose what really set me off was how excitable everyone was that the additive discovered in Waltrip’s intake manifold was “rumored” to be a component of jet fuel.

Even if this turns out to be true, this is sensationalism at its finest.  While the words “jet fuel” might conjure up images of sleek fighters ripping through the sky or demonstration-only dragsters screaming like bats-outta-hell down the 1/4 mile, the truth is that jet fuel itself isn’t very exciting.  It’s darn similar to diesel fuel, though they differ dramatically in additives.

But what about all the over-the-counter fuel additives available to you?  In a classic case of life imitating art — the art of BS in this case — check out this description of STP’s Gas Treatment:

“STP Gas Treatment improves quality of gas by adding powerful cleaning agents to help fight accumulation of harmful carbond, gum and varnish deposits in the fuel system that can reduce performance.  Also engineered to remove water, which can lead to fuel line freeze.  Thsi product is made with Jet Fuel, a high quality carrier of active ingredients.  This product is safe for all gasoline engines.”

Let’s tear that apart and see what it really means — past the jump.

Note first that STP uses the phrase “Jet Fuel” — the capitalization, apparently, indicating that this is a proper name for a product of some sort — as opposed to plain ‘ole “jet fuel,” which is the fuel used to power jets.  The sentence then goes on to describe “Jet Fuel” as “a high quality carrier of active ingredients,” which (again very subtly) indicates that “Jet Fuel” is an inactive ingredient.  Or more precisely, it’s unimportant filler that carries the tiny amount of real stuff around.  Think of Jet Fuel as the inert powdery crap in pills that helps to distribute the few milligrams of actual medication.

So did Waltrip put STP in his fuel?  It’s doubtful.  My guess is that the ‘trip wanted was additional octane.  As far as I can tell, there are really three purposes for fuel additives:

1) Cleaning Your Fuel System

This is a laudable goal.  Over time, some of the varnishes and other nastiness in gasoline will indeed separate out and deposit themselves in your fuel system, and running a decent cleaner through your engine every so often will help to keep those deposits from growing.  Cleaning is also generally responsible for the “saves gas” print on additive packaging as it’s true that a cleaner fuel system will help efficiency.

But what many additive marketers fail to tell you is that this is a relative thing.  If you’re fuel system is already quite clean, you’ll see no improvements in power or mileage by running cleaner through the system.  Even if your system is slightly dirty, you’re not going to see life-chaning mileage bumps.

In fact, the most profound experience I’ve had to date with cleaners came from running some injector cleaner through my 1993 Miata, which hadn’t seen any since I’ve owned it (and probably not before).  After I burned a full tank with the cleaner, the car did seem to run a little smoother, and I thought I might’ve sensed a little increase in performance.  Maybe.

2) Boosting Octane

Look, I’m no fuel engineer, but after spending a lot of time under the hood, I can tell you this: Octane is most simply described as a measure of fuel’s anti-knock properties.  “Knocking” is caused by fuel succumbing to the very high temperatures and pressures within the combustion chamber and igniting before the spark is delivered.  This is a bad thing as the mis-timed explosion causes the cylinder to push against the engine’s normal operation.  It causes extreme stress to the engine in a variety of methods.   Higher octane fuels can withstand higher temperatures and pressures without pre-igniting.

While cleaners generally claim to “save you gas,” octane boosters claim to deliver “increased power.”

To some extent this is true.  As you increase the compression of an engine, you’ll need higher and higher octane fuel to prevent pre-ignition.  Since many modern engines feature computer-controlled timing complete with a “knock sensor,” they can retard the timing when they sense knocking to prevent damage.  Retarded timing, of course, means less power.

So theoretically, if you were running your computerized vehicle on fuel with too low an octane rating for its compression, and you then upgraded to higher octane fuel, you’d likely see a performance gain from the correctly-adjusted timing.  But the vast majority of engines today are designed to run correctly on 88 octane fuel — the lowest normally available.

The bottom line: If your car is designed to run on 86 or 88 octane fuel and you fill ‘er up with 93, it’s not going to make a damn bit of difference — except to your wallet.  The same goes with aftermarket “octane boosters.”

As you might guess, if Waltrip could increase the octane of his fuel beyond that of his competitors, his crew could then adjust the engine to take advantage of this to make additional power

3) Preventing the Absorption of Water

I’ll admit that, having lived in Texas most of my life, I don’t really know much about these additives.  I understand, though, that gasoline can absorb water whle jet fuel doesn’t, so freezing water is far more of a risk in jet aircraft than in gasoline-powered cars.  On the other hand, in the wintertime up north, it can get cold enough to cause problems, so I’ve heard of people using additives to protect their vehicles.


It’s my firm opinion that unless you’ve made modifications to your engine that require additional octane, and unless your fuel system is seriously dirty, you’re not going to see any benefit at all from additives like the one pictured at the top of this post.  You may feel better about yourself or even get a warm-fuzzy inside because you’re taking care of your car, but that’s the limit of the benefit.  Your car can do without.

Of course, if you have a different opinion, I’d love to hear it in comments.

STP Gas Treatment [STP]


27 Responses to Cutting Through The BS: Fuel Additives

  1. Eric says:

    wikipedia has a pretty good explanation of how octane ratings are derived:


    I remember in my sophomore organic chem class having this explained to me and having a real “ah-ha” moment. Thanks for putting this up, it’s great to see the championing of critical thinking and rationality for a market that pretty saturated with hyperbole.

  2. olderty says:

    Nice write up. I’d like to add a couple things though. Most ‘premium’ gases, mostly 93 octane, do advertise that they contain cleaners. Your point that higher octane fuels don’t do anything but affect your wallet is true for the most part (most cars don’t need the extra octane), unless it makes you feel better that there are cleaners inside. The way I see it, premium (93 octane) usually costs around 20 cents more per gallon than the standard 87 octane. If you buy 10 gallons of 93, you’re spending $2.00 more than you normally would. The cleaner/octane additives you buy inside the gas station usually run between $3.50-$6, and usually only treat 10-15 gallons. My personal fuel maintenance is usually a tank or 2 of premium name brand gas once a month or so. In other words, buying premium is better when it comes down to money.

    The second thing I’d like to point out is that the fuel/air mixture in a cylinder is not supposed to explode, as you stated, when operating normally. Gas is designed to burn – very fast, creating the energy necessary to move the piston back down. When the fuel/air mix explodes (as you said, called ping or knock) it is a bad situation that will cause damage if not corrected by the computer or higher octane gas.

  3. SlowJoeCrow says:

    From personal experience, octane boosters are only really useful if you have a high compression engine that pings on 93 octane. Before I rebuilt it with flat top pistons my BMW R100S needed octane booster, and in the early 90s I used 104+ Real Lead , which came in metal containers because it would melt plastic. I found that out the hard way, when I put some in an empty VW fuel additive bottle to save space on a trip, and when I took it out of the saddle bag the bottle was soft and squishy.
    Fuel line driers, like Dry Gas are mostly alcohol and serve a useful function in the winter by sequestering water from condensation in the tank and preventing it from freezing. I have had a car not start because of ice in the fuel line so it is a real problem in cold damp climates.

  4. Adam says:

    I tend to run a fuel / injector cleaner additive through my car every second oil change or so. Typically I find that when I do that, the car will run smoother after, and start somewhat easier. I’m not sure how much of that is purely psychosomatic, but I know for a fact that it’s helped on some of the truely abused used cars i’ve owned over the years…

  5. Roscoe says:

    Chuck- your Texas climate shows through here. In a Northern winter, it’s a good idea to run a good multi-purpose fuel additive through the tank every moth or so. More than anything, I think it helps with water in the fuel lines. I’m not too diligent about it in warm months, but I can definitely feel and hear the difference a good additive makes in the winter, we do so in all our equipment.

  6. nrChris says:

    Isn’t jet fuel just kerosene? Seems like that would be a really bad thing to run through a normally aspirated engine.

  7. PT says:

    The issue was because Daytona is a restrictor plate (The plate restricts oxygen flow to slow down the cars) track. The story says that it was an oxygenate that was added. A quick check of Wikipedia under Oxygenate confirmed that it will help you burn more of the fuel that the restrictor plate is wasting. No modification would have been necessary to the race, to take advantage of additive. You are entirely correct that it wouldn’t help too much the average car as long as you use the proper fuel and keep up with the basic car maintenance.

  8. Chris S. says:

    Ive used Seafoam before which does seem to make a difference

    you suck it into your engine through the break booster line and let it sit for 10 minutes then start it up and watch the smoke show as your exhaust spits out lot of carbon build up

    Check out some videos

  9. Paul says:

    Well a buddy of mine used to own a gas station and he knew a thing or two about the product he was selling. First thing I can recall him telling me is all gasolines on the market today are detergent gasolines. That is they clean as you use them. Some companies make a big to do about having cleaners in their gas, but if my friend is right all gas has cleaners in them.

    As for lead, the only reason I know of for lead in gasoline is for valve seat lubricant. Maybe it did something else, but running unleaded in non stellite valve seat heads would lead to impacted valve seats. Alloy valve seats is afaik the main difference between vehicles that can run on unleaded, and those that need lead.

    It is my opinion that we are getting scammed with this “oxygenated” fuel ethanol today. Mileage really takes a dive when this stuff is in the gas. And yes, I have had fuel lines freeze on me, and drygas can prevent that from happening. I’ve also seen people that swear by Marvel Mystery oil in their gas. I’m not one of them though.

    I am a big believer in oil additives though. I have seen Tufoil do amazing things.

  10. Fong says:

    Lead was originally used as the anti-knock agent from 1927 to 1986 when it was finally outlawed. The other option was ethyl alcohol that farmers had been using already but lead was chosen ‘cuz it was cheaper.

    This a great writeup. I can’t count how many middle class suburbanites I’ve had to educate on the uselessness of using higher octane than their car requires. What’s especially curious is that they always sound surprised…sheep…

    • Anne says:

      My car engine began missing. I had been running the cheap gas. When I filled up with premium it took about ten minutes to stop. It can make a big difference depending on what fuel your car requires.

  11. Old Donn says:

    Unless you’ve got a Vette or a Viper, your car was built to run on 87 octane regular unleaded. That’s what the on-board computer’s looking to ignite. Running premium will cause deposits because it won’t burn as efficiently as regular. Any mechanic who says otherwise should be selling shoes. Back in the day of breaker points and mechanical timing, you could make it work, not in these on-board computer days. As far as additives are concerned, gas in the tank, oil in the engine, nothing else.

  12. Rann Fox says:

    Look I don’t know jack about the finer points of IC engines BUT on one car I have noticed several items of FACT;
    1 The car is a 98 Chevy Caviler (4 banger)
    2 I drive appox 250 + miles a week
    3 Regular gas makes it sluggish and gives poor gas milage
    4 Premium gives me up to 10 miles per gallon better milage
    5 STP additive gives me more “peppy” and responsive to the throttle
    6 The car is a one owner and runs ONLY chevron gas
    Now does some one want to explain that or do I continue to think this article is BS????

  13. HS says:

    Damn, if your mileage varies up to 10 miles from gallon to gallon, there’s more going on than just different fuel types.

    Also, I hate to be the 10000000000th person on the internet to point this out, but real-world, “seat-of-your-pants” experimentation is hardly useful when there are so many variables to address.

    Gasoline composition can vary from season to season, and you didn’t even address that effect in your experiment. Did you control for things like ambient temperature, humidity, wind, altitude, road surface and tire pressure variations? There are hundreds of things that can significantly contribute to variations in fuel efficiency.

    There’s also the human factor to consider. Was this a double-blind experiment? If not, what steps did you take to minimize the psychological factors of the experiment?

    I would hesitate to call BS on conclusions drawn from the results of countless controlled, scientific experiments when all you’ve got to go on is non-scientific observation.

  14. Old Donn says:

    Bravo Trevor. If the above mentioned Cavalier was like that from the get, it should’ve been back to the service department in a heartbeat, (of America?). There are exceptions, but facts are just that. What shape is this machine in? Or did you buy into the “everything lasts 100,000 miles” story. And before you ask, yeah, I’ve have Cavaliers and their cousin, Pontiac Sunbirds, in the past. They had problems, (head gaskets, fuel pumps), but all ran as advertised on regular unleaded.

  15. Old Donn says:

    The above should read Bravo HS.

  16. Rann: My theory is that you have carbon buildup in your cylinder heads, which reduces the available combustion chamber volume and increases the compression ratio, leading to knock and thus spark retard when you’re using low-octane gas. Premium allows the engine to run closer to spec, and you recover some of the lost power.

    Find a friend with a borescope you can put in through a spark plug hole, or take it to a service shop and ask them to inspect it for excessive carbon in the head. This can be caused by prolonged operation at low throttle (how often do you run at wide-open throttle for 5+ seconds at a time, like get on the entrance ramp and just womp on it?), dirty injectors, or restricted intake (changed your air filter lately?).

    Anyway, water remover doesn’t work by segregating the water from the fuel — that happens normally. Oil and water don’t mix, right? So water vapor that gets into the tank condenses and collects in a “puddle” on the bottom of the tank, since it’s heavier than gasoline. Occasionally the fuel pump sucks up part of this puddle, and a moment’s worth of water gets delivered to the injectors instead of fuel. This causes periods of rough running, power loss, even stalling if there’s enough of it.

    Water remover is just alcohol, which is combustible like fuel but also dissolves water. It mixes with the puddle in the tank, so next time the fuel pump sucks some up, the engine doesn’t notice (much). Running a few gallons of E10 instead of your regular fuel has the same effect as adding a bottle of additive, but costs less and has no additional packaging to throw away. In spring and fall when condensation is most likely, I stop at the local Sunoco every few fillups, because all their blends contain 10% Ethanol.

    At most stations, even the cheap grades contain the same detergents and additives as the higher grades. But the specific types of additives vary between brands. Every detergent has a set of things it will dissolve, and a set of things it won’t. It’s like moisturizing hand soap won’t clean moisturizer off your hands. Running different brands of gas (with different additives) allows them to clean up the mess left behind by each other, and has the same effect as a bottle of additive but without the cost or the bottle.

    As for high-compression engines, it’s not just Vipers and Vettes! I was shocked and somewhat pissed off when, a week after having bought my Toyota, I stopped to fuel it up and found the “premium fuel only” sticker inside the fuel door. The dealer never told me that the tradeoff for having the upgraded “2ZZ sport” engine was that I’d be paying for high-octane gas for the life of the car! Bastard. Anyway, a lot of the smaller cars achieve the performance they do because of high-output, high-compression engines, which require high-octane gas. If this is the case, it’ll be in the owner’s manual or labeled inside the fuel door.

  17. ambush27 says:

    I don’t think fuel additives are necessary, it is probably just as good or better for your car to just put some top tier gas in.
    I think that crap gas and idling for long periods of time as well as improper maintenance are more likely to kill an engine.

    And although I’ve heard of additives for fuel line freezing, fewer and fewer people seem to be doing that, maybe its the move to fuel injection, maybe its the additives in gas, I don’t know, but it seems unnecessary.

  18. fuel saver says:

    I’ve been using a fuel additive consistently for several years and I think its been helping increase my overall mileage just as much as it says it would. It also allows me to use lower octane and still get good performance.

  19. melvin says:

    Second that it’s not just Vettes and Vipers. Practically anything with forced induction is going to call for premium gas.

  20. Teacher says:

    For folks that run just one brand of gas, the gas you think you’re buying may not be that brand. Companies often “trade” gasoline. Texaco will make an agreement with Exxon where texaco services several Texacos and the one exxon in the area while Exxon will service several Exxons and the two Texacos in the area. I know it happens as one of my cousins drives a fuel tanker. He frequently delivers, from the same truck, gas to two or more brands of stations.

  21. Cargrl says:

    I love STP. My dad and uncles have used it as “preventitive medicine” and our cars have always done right by us.

    You want to talk snake oil, I wonder why you’re singling out STP. At least they’ve got active incredients that really do work to clean your engine. Take Lucas for instance… is LITERALLY mineral oil. Its got NO ACTIVE stuff in it.

    What a racket.

  22. jennifer says:

    can i ask some of the product of fuel additives? how much the price of 1 barrel of fuel additives and the brand of the said products? thanks i really need your answer right now..

  23. bob says:

    Chevron and Shell and 1 other eastern feul company (sunoco/conoco/amoco/BP?) spent millions suing each other; the end result is these 3 can all claim “none better” at preventing engine buildup. Chevron Shell and (?) use better quality additives than other companies, additives which will keep an engine cleaner over the long haul.

    Most cars run fine on regular. Most newer cars will recognize premium and deliver modestly better performance. Most additives won’t deliver near what they promise.

  24. Mark says:

    The jet fuel is kerosene. farmers and racers used to add it to fuel to keep carbs clean

  25. Sylvan says:

    I have a Lexus LS and a BMW 750 M sport .
    Considering these cars cost over $200,000 in total I figured why not use 93 Octane and STP as it certainly cannot hurt

    The mechanic who recently suggested DRY gas said “If you don’t use your cars for a long time add dry gas to it”

    The BMW is my summer GREAT weather car as the run flat Pirelli tires SUCK in the rain and are impossible to drive in the snow even as little as 1/4″

    The LS is amazing in all weather but having a V- 8 and a V- 8 twin Turbo charged is a fun car to drive

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