Do Fuel Additives Work?

Store shelves are littered with additives for fuel that claim to provide a number of benefits, including…

• Increased fuel economy
• Smoother engine operation
• Reduced emissions
• Extended engine life
• Maximum horsepower

Do additives for fuel work, though?

A quick Google search reveals multiple articles that claim they don’t. There must be a good reason so many people regard fuel additives with skepticism.

That’s because, while most motorists expect to see the benefits promised by fuel additives immediately, it takes several tanks of treated fuel before most additives provide any noticeable performance improvement. That doesn’t bode well in a society used to getting what it wants, when it wants it.

Engine condition plays a vital role in fuel-additive performance

Here’s what often happens.

Over time, performance-robbing deposits form on your engine’s fuel injectors, valves and in the combustion chamber. Today’s injectors are highly engineered to tight tolerances, and even minute deposits interfere with the spray pattern and reduce power and fuel economy.

The problem is especially pronounced in high-pressure common-rail (HPCR) diesel engines and in direct-injection engines that locate the injectors in the combustion chamber, exposed to intense heat.

Eventually, you notice a reduction in power, throttle response, fuel economy or drivability. You pick up a fuel additive at the gas station or parts store.

“Increases Fuel Economy!” it proclaims. “Outstanding,” you think as you empty the bottle into your fuel tank.

Are fuel additives one and done?

But, by the time you pull up your driveway, nothing has changed. Or again the next day after you arrive at work. What went wrong?

Technically, nothing. You likely bought an inexpensive additive that contains minimal cleaning agents. If you continue to buy the additive and use it with every tank of fuel, maybe over time – could be weeks to months – you’ll experience a slight up-tick in power, fuel economy or drivability.

Then you can continue to use the additive to maintain engine performance. The additive did, indeed, work and it did live up to its performance claims. It just didn’t do it quickly or dramatically enough.

Fuel-additive concentration matters

It takes a fuel additive formulated to the correct concentration to deliver immediate results. But most additives for fuel simply don’t contain a sufficient concentration of cleaning agents to provide immediate results.

That’s where AMSOIL is different.

P.i. Performance Improver is a potent, deep-cleaning gasoline performance improver featuring concentrated detergents that aggressively clean stubborn, power-robbing deposits from injectors, valves and combustion chambers. It reduces emissions and increases fuel economy up to 5.7 percent.¹

Best fuel additives.
AMSOIL P.i. fuel additive

Works in GDI engines, too

It also works well in gasoline direct-injection (GDI) engines. In GDI engines, injectors are located inside the intense heat and pressure environment of the combustion chamber, making them particularly vulnerable to deposits. Extreme pressure combined with incomplete fuel combustion can lead to dramatically increased soot (particulate matter) levels.

Direct injection typically creates 30 to 40 times more soot than port fuel injectors (PFI). Even a minimal amount of injector fouling can lead to increased pollution and wear and decreased power and fuel economy.

P.i. removes stubborn deposits and keeps injectors functioning as they should. Testing shows P.i. restored GDI fuel injectors to a 100 percent flow rate after one tank of fuel.²

GDI Injector Flow Restoration
ASMOIL Performance Improver Gasoline Additive


How about upper-cylinder lubricants?

Many additives for fuel are marketed as upper-cylinder lubricants. The intense heat of combustion and limitations of the oil-control piston ring result in a lack of oil at the top of each cylinder. This can lead to ring and cylinder wear that reduces engine compression, decreasing power and performance. In step a range of fuel additives promising vital lubrication for the engine’s top-end, maximizing protection and performance.

Again, though, some additives don’t provide much, if any, lubricity improvement, as the chart shows. AMSOIL Upper Cylinder Lubricant, however, delivers 18 percent more lubricity than Lucas³ and 20 percent more than Sea Foam³ for better retention of horsepower and fuel economy. It also fights ethanol-related corrosion.

Best fuel additives.
AMSOIL Upper Cylinder Lubricant

Buy Upper Cylinder Lube

Don’t forget the diesel fuel additives

For peak performance, diesel engines need a daily dose of detergent for cleaning and lubricity to protect the injectors and fuel pump while keeping the combustion chamber clean.

And don’t forget Quickshot for your small engines and powersports equipment. It cleans performance-robbing deposits, stabilizes fuel during short-term storage and fights ethanol problems.

So, yes, fuel additives do work – if you use the right ones.

¹ Based on independent testing using EPA tests: Federal Test Procedure 75 (FTP), Supplemental Federal Test Procedure (US06), and the Highway Fuel Economy Test (HFET). Average fuel mileage increase of 2.3 percent.
² ASTM D5598(M) – 2013 Buick Regal test vehicle
³ Based on independent testing of AMSOIL Upper Cylinder Lubricant, Lucas Upper Cylinder Lubricant and Sea Foam Motor Treatment obtained on 02/13/2019 using the ASTM D6079 modified for use with gasoline.

Updated. Originally published Jan. 3, 2018.


  1. I as an AMSOIL Dealer have used the P.I. in my engine, and then a short time later changed my plugs, which had 147,000 miles on them{ I have the old plugs to prove it also} and when the mechanic took the out, he said he was very surprised. I asked him, “Why” He said the plugs are spotless, nothing, no carbon or any kind of build up was on them. They were as clean as could be.
    The AMSOIL P.I. really does do what it says.

  2. Curious to know how such fuel additives might clean the valves on a direct injected engine. Clean the injectors and the tops of the pistons? Sure. But the intake valves?

    1. Hi Mitchell,

      They can’t since, as you allude, the fuel doesn’t wash across the backside of the intake valve. Additives can only clean what the fuel touches. Notice the valves pictured above are from a port-fuel-injected engine. As noted in the post, however, P.i. does an excellent job cleaning GDI injectors.



  3. I am sorry but before I used amsoil fuel additive I was getting 17 mpg in my 2013 Honda CRV which I thought was terrible. After I added amsoil I now get between 10 and 13 mpg. I am using the same gas station as I have always used.

  4. If you consistently use a Top Tier gasoline with additives blended for the local climate, a new engine will stay clean and run properly. Letting an older engine get full of gook over the years will not be cured by ANY additives, including the Amsoil PI that is being touted here by yet another pyramid scheme distributor.

    1. Hi Terri,

      Thanks for the input. Isn’t it great to live in a country where you don’t have to buy a product from a company you don’t like if you don’t want?

      Thanks for reading.


  5. Add a pint of automatic transmission fluid to each tank of gas – worked like a damn on the farm. Kept spark plugs and injectors clean

    1. i would not think ur catalytic converter would like having all that OIL passing thru it… a friend had a car that used a “little” oil, not amsoil, it eventually plugged up, car could not be driven anymore… engine idled, but could NOT reach 20 mph… also i had a car that had 3 bad valve seals, as it turned out, used VERY little oil, way back in ’79… was brand new, & it fouled out the plugs… gave a bottle of P.I. 2 a friend, who used it in his newer honda… was surprized… seemed 2 give him better mpg… imagine that…

    1. Hi Nick,

      True, fuel additives won’t clean the back of the intake valves in a GDI engine, but they still clean the fuel injectors and combustion chamber, which helps improve fuel economy. Check out our white paper on AMSOIL P.i.. Scroll to page 7 and you’ll see the results of testing performed on a VW Jetta GDI. AMSOIL P.i. improved fuel flow an average of 2.3%.

      Thanks for reading.

  6. I’ve spoken with so many people who purchase fuel additives, and wonder why they don’t work. Then I ask them what brand they use, and where they get it from. They say they get it from the dollar store. I tell them I’m sorry, but the additives they sell at the dollar store just won’t cut it, unfortunately.

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