Mileage increase from fuel additives?

[Todd S. Malicoate]

17 years of selling this stuff, and I'm still not convinced they are effective, or that one brand is better that another. I'm, of course, asked daily what I think is the best additive. I steer the customers toward the little bottle of Lucas fuel additive, because it is the least expensive.

People buy these because they want to feel good about buying something that will help their car last longer, but don't want to put the effort into regular maintenance. Here's a free tip...the best thing you can do for your car is do your oil changes every 3,000 miles and follow the manufacture's schedule in your owner's manual on the other maintenance. Leave the "dump-in" miracle-fix products for the chumps.

Someone with some initiative should start a company and market some of these products...I even have a name for you..."Miracle in a Bottle." They will sell at about the same rate as the Lucas, STP, Gumout, Berryman, 3M, Valvoline, and Chevron products...just make sure you have an eye-catching bottle design and graphics. Also remember to include a product that neutralizes the harmful effects of ethanol in your gas tank...that will sell like wildfire.

[windshieldbug]

I steer the customers toward the little bottle of Lucas fuel additive

Does it then make your fuel gauge work intermittently!?

[SplatterTone]

I recently tried adding a gallon of gas to the gas in my tank, and IT WORKS! I went further before I needed to fill up again.

[TubaRay]

I recently tried adding a gallon of gas to the gas in my tank, and IT WORKS! I went further before I needed to fill up again.

Amazing!!?!

I'm going to go out on a limb and guess that the number of miles further you were able to drive on that tank was approximately equal to the number of miles per gallon you usually get in that vehicle. Am I anywhere close?

[SplatterTone]

Am I anywhere close?

I dunno. They didn't cover that high end math by the time me and Jethro graduated with a fifth grade education.

[iiipopes]

It is my opinion from trying gasoline additives in everything from Ford Tempos, to high-dollar "luxury" sedans, to pickups and SUV's, to my 1967 Jaguar E-type, that gasoline additives do not, in and of themselves, increase gasoline mileage. They are not gasoline. They don't burn with the same efficiency. They (especially if alcohol based) all have lower BTU and equivalent octane ratings, and actually lower gas mileage in an absolute, abstract analysis.

BUT, and again I sat BUT, what the right additive can do is dissolve deposits on the working parts (like the back sides of valves and the nozzles of injectors, when using a solvent-based additive) or clear and help pass impurities from the gasoline in the tank, (as condensation or even dust with alcohol-based additives) so that the engine runs cleaner, and therefore, in conjunction with proper oil changes, all filter changes, and tuneups, with more efficiency. The cleaner and more efficient operation of the engine is what promotes a slightly marginal increase of efficiency, which we call better gas mileage, and its corollary, cleaner emissions.

[Todd S. Malicoate]

The cleaner and more efficient operation of the engine is what promotes a slightly marginal increase of efficiency, which we call better gas mileage, and its corollary, cleaner emissions.

Darn it...I was all ready to say "wonderful post...I couldn't have said it better." And then that last line.

Better gas mileage, by itself, does not equal cleaner emissions. At least not in combustion engines. You can tune the engine for the best emissions and the mileage will be terrible. Alternatively, you can tune the engine for the best possible mileage and the emissions will be worse than they otherwise could be.

There are three factors designers must consider...mileage, performance (horsepower/torque), and emissions. Think of them as points on a triangle. Maximize one, and the other two suffer. The best engineers can strive for is a point directly in the middle of the triangle.

In searching for the middle of the triangle, they came up with the stoichiometric ratio (the optimum ratio of air to fuel for complete combustion) which we are now familiar with for gasoline engines...14.7 parts air to 1 part fuel (by weight, not volume). Interesting to note that ethanol has a stoichiometric ratio of 9:1...more fuel needed per unit of air...no wonder the mileage goes down when you add ethanol to gasoline.

[SplatterTone]

Another additive that worked well for me was a nuclear reactor. What a great mileage booster! I like to cover the car with mushroom cloud bumper stickers and drive around San Francisco.
You CAN hug your child with nuclear arms.

[Rick Denney]

The best engineers can strive for is a point directly in the middle of the triangle.

Depends on the political season, of course. There have been times when emissions outweighed all other considerations, and other times when fuel consumption was the prime directive. Performance has always been a bit down in the priorities, since about 1971 anyway.

They have improved performance as a result of improving efficiency, even though that was only partly their intent. Those two factors are reasonably close together. If the throttle is opened fully with the engine in economy mode, the quick result will be detonation and burned components.

In economy mode, engines run very lean to make sure that an abundance of air uses up all the fuel. At part throttle, this does no harm. But this is how they make them efficient.

In power enrichment mode, engines run rich to make sure that an abundance of makes it possible for every bit of air to make power. At part throttle, this is wasteful. In the old days, they switched from one to the other using vacuum (e.g. the Rochester Quadrajet's Power Valve) as a measure of power demand. The more open the throttle, the less the vacuum.

Now, they use the mass airflow sensor and throttle position sensor. But a wide open throttle will immediately take an engine out of closed-loop economy mode (where it looks at the oxygen sensor) and put it into the table-lookup open-loop mode, which will be programmed to run rich at wide-open throttle.

Another difference is that port fuel injection is far more consistent one cylinder to the next in delivering fuel, making manifold design to distribute air evenly much easier. So "rich" to a modern engine management computer will not be as rich as it was in the Quad's Power Enrichment mode, which might have been as rich as 12:1 in some applications. But economy mode might even be leaner--as high as 17:1. Only in the middle power management range do systems go for the stoichometric ratio, which is popularly believed to be most efficient. Computer controlled fuel injection can respond to power demands by adding more fuel directly, rather than waiting for various power enrichment circuits in carburetors (that were usually clogged anyway in older cars) to kick in. That's why performance has improved alongside efficiency. (Another reason is general reduction in engine friction. Most engine are now smaller and have smaller bearing surfaces, and use roller cams, etc. And still another reason is more efficient combustion chambers, with four valves per cylinder, etc.)

Additives usually don't help the cleanliness of an engine much, in my view. Any sludge is probably better left where it is, or prevented by using any decent detergent gasoline. After it builds up, knocking it loose can do bad things.

But I would steam-clean the inside of an engine in preparation for rebuilding. This will identify just how little most of these additives do: I could make the engine spotless on the inside by running the engine at 3000 RPMs, and very slowly pouring a gallon of water down the carb barrels. if the water went in slowly enough, it would not kill the engine, but it would flash-boil on contact and steam-clean the combustion chambers. On occasion, though, a flake of crud would fall off a valve and do it in, which is why I only did it on engines I was getting ready to overhaul.

One of the additives I like and use is Sta-Bil, which is alcohol-based and which helps prevent the good parts of the fuel from evaporating off and leaving varnish. I used it in my motorhome, which doesn't get driven frequently.

Rick "who is good friends with several GM execs, including a guy who ran the truck carburetion group back in the day, and another guy in charge of engineering for one of the branches" Denney

[iiipopes]

What Rick Denny said. After reading the followups, I got my SU carburettor book back out and read some more. In summary, a slightly rich mixture gives the most power, using more gasoline, of course; a medium mixture will give the most efficient burn to CO2, and a lean mixture, while having more efficiency at the expense of a slightly higher combustion temperature, will actually start producing more NO emissions. So, I looked for a link that could put it all in perspective:

http://www.roversd1.nl/sd1web/carburation.html" target="_blank

Notice the view under the bonnet of the E-type as you scroll down is a right-hand drive model.

And this one: http://www.sw-em.com/su_carbs.htm" target="_blank

[tubatooter1940]

I believe mildew was invented right here in Alabama. I pour a bottle of injector cleaner in my cars every fifth or sixth fill up. I have never had to clean plugged up injectors.
A tankful of diesel in my sail boat lasts over a year unless I do a long cruise. I have to add an alge killer (Bio-Bor) to my diesel fuel to keep that stuff from growing in my tank.
None of this goop increases milage.