To Add an Additive or Not

We have had a number of questions come in about oil and fuel additives.


Should they be used with Harley Davidsons?

Which oil additive is best for my air cooled Harley?

Via Email


Using an oil additive is actually “old school thinking”. Many years ago the oil that was available to us did not offer much protection for our Harley Davidson motorcycles. In 1941 ZDDP (Zinc dialkyldithiophosphate) was developed and manufacturers began to put it in their oils. Even today, ZDDP is the most commonly used anti-wear additive in motor oils. It contains both Zinc and phosphorus components that work together to provide anti-wear protection and minimize lubricant breakdown. ZDDP also has mild extreme-pressure protection. Zinc, viscometrics, and base stocks are the oil contents that control the wear of moving metal parts. However, while Zinc is important in protecting against wear, the biggest concern should be in using a well balanced oil that is designed for its intended application. ZDDP works by decomposing when temperatures rise and surfaces come closer together. The resulting chemistry is what protects the critical, working metal surfaces.

So why not use an oil additive?

Won’t adding more ZDDP give even better protection to your 20/50?

Well, the old saying, “too much of a good thing can be a bad thing” rings true here. Whether you are running Screamin’ Eagle, Bel Ray, Spectro oil….. these oils are all balanced and already have the correct amount of ZDDP for their intended application which is your Harley Davidson. If more ZDDP is added, it will just burn past the rings and collect in the exhaust ports and in the exhaust system. If your Harley has a catilidic converter, it will become coated and eventually blocked from the excess ZDDP burn off, restricting the motor from breathing correctly.

There are automotive and diesel applications where oil additives are beneficial. However, when it comes to your Harley Davidson, a quality synthetic oil is best.

In regard to Fuel Additives:


Ethyl alcohol, or ethanol is a grain alcohol fuel additive usually made from corn. In America, Ethanol is blended into our gasoline for two main reasons: To reduce our dependency on foreign oil and to help reduce tailpipe emissions.

In gasoline, Ethanol is used as a biofuel filler. Ethanol is an octane booster and an oxygenate. Pure ethanol has an octane rating of 130. Oxygenates are compounds that contain oxygen in their chemical structures and contribute to the combustion process. Oxygenates help to eliminate unburned hydrocarbons by helping them burn.

Most gasoline in the states contains up to 10 percent ethanol and is called E10. E10 is known to cause problems for fuel systems on older motorcycles especially during long term storage. Ethanol is corrosive. It can cause hoses and gaskets to swell or deteriorate. Pre-2000 bikes are much more ceceptable to these issues. Ethanol resistant fuel system components are used in almost all bikes & automobiles manufacturered after 2000.

Even if your motorcycle was made after the year 2000, you can still have issues with ethanol if you leave your motorcycle in storage for an extended period of time. Sometimes as short as thirty days or, more commonly, a (winter) season is enough for fuel to turn bad.

This is because ethanol is hydrophilic. Which means, it attracts and binds to water. Even to water vapor. If ethanol absorbs enough water, it separates and sinks to the bottom of the fuel tank. Ethanol is the primary octane in gasoline. So when the ethanol separates & sinks, the gasoline toward the top of the tank could end up with an octane rating in the lower 80s. For this reason, it is important that a fuel stabilizer is added when you plan to park your motorcycle for an extended period of time.

There are a number of good choices when it comes to fuel stabilizers for your Harley Davidson. There are a lot of well known companies that manufacture fuel stabilizers and additives. Some are considerably more expensive than others. Ask your buddies what they like, or what they have used. Find what fuel additive might work best for you to keep your fuel system clean.

Related Videos:
Pick Your Ride and Learn How to Change Your Oil, Transmission Fluid, Primary Fluid and more
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21 Responses to “To Add an Additive or Not”
  1. Mick

    Hi guys.
    Is there any benifits by using screamin eagle engine oil in a 2017 FLS stock 103 engine with Screamin eagle tuner, Vance & Hines Big Shots and stage 1 air filter.
    Thanks, Mick.

  2. Anthony Didominico
    Anthony Didominico

    What about adding 2 stroke synthetic oil to your gasoline for added upper engine lubrication. Today’s gas is junk , been using 2 stroke oil added to my gas for 20+ years without a single issue. All my bikes are carburetored.

    • maydaymj56

      Marvel mystery oil is what I used in my pan,shovel heads.and had long gevity results. Real clean and hardly any wear after thousands of miles.

  3. Poppa Smurf
    Poppa Smurf

    I often wonder why y’all keep talking synthetic oil in Harley, you make it sound like that oil is the best for ALL Harley Davidson’s and I am old school and ride an old school Harley,,, and I did try Synthetic three different oil changes and all it did was deplete my wallet more. I have over 200 thousand on an old 88 1200 Sporty and have had five clutches, one top end and one bottom end, using conventional oil except for the three times I did try it,, not convinced that syn oil is for EVERY HARLEY.. and y’all keep forgetting not all of us who ride ,, have a bike that is less than four years old…just saying,,, most of your articles I still enjoy and will continue to subscribe, the Sportster disk were interesting.. ..poppa smurf,,, bicycle

  4. Allen

    My Harley’s shifter started sticking on the last ride. Appears to be staying put after changing gears instead of allowing me to go to next gear

  5. George Brader
    George Brader

    Can I use marvels mystery oil to my gas and oil,and if so. How much to each. Thanks.

  6. William Shore
    William Shore

    Headlight and passing lights stopped working, but running lights and turn signals work???

  7. Ted

    Purchased complete service Video for 2017 custom sportster, now I need one for 2018 Harley low rider! Do you have video on basic maintenance for 2018 low rider?

  8. msandman57

    Use name brand oil and the correct viscosity recommend by the OEM, change it on time. Todays engine oils are formulated with a balanced package of additives that allows the base oil have extended life, cleans the engine components and reduces wear. Adding additives is a crap shoot at best. When the additives get used up, the base oil ages faster. Better filters (air and oil) also help extend oil and engine component life. Synthetics do work better, last longer and take heat better. Keep it clean and changed.

  9. Aaron Gilmer
    Aaron Gilmer

    I have a 98 dyna. Would adding an additive to my gas(carb cleaner) help with my back fire upon start up.