AMSOIL vs SYN3
Screamin’ Eagle SYN3 is Harley-Davidson’s own house-brand oil, made under contract by a third-party refiner. It’s also been quietly reformulated. Here’s the real story on what’s in the bottle now, versus AMSOIL’s dedicated V-Twin motorcycle oil.
Alan Williams · AMSOIL Direct Jobber #1243776 · Tomball, TX · 225-441-6397
Official Manufacturer Data
Motorcycle Oil vs. Motorcycle Oil
SYN3 is a three-in-one fluid for the engine, primary chaincase, and transmission, so the fair comparison is AMSOIL’s dedicated V-Twin Motorcycle Oil, not a passenger car product. Here’s what each manufacturer actually publishes.
| Spec | AMSOIL V-Twin Motorcycle Oil | Screamin’ Eagle SYN3 |
|---|---|---|
| Who actually makes it | AMSOIL INC, Superior, WI | Citgo Petroleum, Houston, TX, per Harley-Davidson’s own published safety data sheets |
| Application | Engine, transmission, and primary (one product, three sumps) | Engine, transmission, and primary (one product, three sumps) |
| Third-party wet-clutch certification | JASO MA/MA2 and ISO-L-EMA2 certified | Not listed among Harley’s own published certifications for SYN3 |
| Factory-recommended engine oil interval | Up to double the stock interval when paired with an AMSOIL filter, per AMSOIL | 5,000 miles, same interval Harley specifies for its conventional H-D 360 oil |
To be fair to Harley: SYN3 is the only oil that’s factory-documented for use across all three compartments (engine, primary, and transmission) on their own service charts, a genuine convenience most third-party oils, including AMSOIL’s V-Twin line, don’t carry as an official OEM designation.
Riding a Milwaukee-Eight, Twin Cam, or Evo? Tell me your model and I’ll confirm the right AMSOIL V-Twin grade.
SYN3 Has Been Quietly Reformulated
This part of the story matters and rarely gets told straight. The older SYN3, the single-grade 20W-50 that shipped for years, was independently analyzed through its own filed Material Safety Data Sheet and found to be a blend of synthetic and conventional petroleum base oils, not a 100% synthetic product, even though it carried the “synthetic” name.
Harley has since released a new SYN3, a dual-grade formula that performs like an SAE 50 at high temperature and an SAE 15W-50 for cold starts, which the company now describes as a “full-synthetic” product built on a proprietary three-basestock formula. That’s a real, meaningful reformulation, and it’s fair to note that Harley’s own current marketing no longer describes it the way the earlier, independently-tested version was formulated. It’s also worth knowing which version is actually in your bottle if you’ve been running the same case for a few years.
Get AMSOIL V-Twin Motorcycle Oil, JASO MA/MA2 certified, at 25% off as a Preferred Customer.
Where SYN3 Is a Reasonable Choice
SYN3 is a legitimate, factory-engineered product with real dyno testing behind it, and Harley-Davidson Factory Racing uses it. It’s a reasonable choice for:
- Riders who want one factory-documented fluid across engine, primary, and transmission with zero guesswork about compatibility
- Owners staying on Harley’s standard 5,000-mile service schedule who aren’t trying to extend intervals
- Warranty-conscious riders who prefer sticking with the manufacturer’s own branded fluid, even though non-OEM oils meeting the required spec don’t legally void your warranty
Common Questions
Is SYN3 made by Harley-Davidson?
Harley-Davidson develops and specs the formula, but per the company’s own published safety data sheets, SYN3 is manufactured under contract by Citgo Petroleum in Houston, Texas. It’s a house brand, not an in-house-refined product.
Is SYN3 a true full synthetic?
The current “new SYN3” is marketed as full synthetic with a proprietary three-basestock blend. The earlier single-grade 20W-50 version was independently found, through its own filed MSDS, to be a 60/40 blend of synthetic and conventional oil. Harley has since reformulated the product.
Is Syn3 for Polaris or Harley-Davidson?
SYN3 is Harley-Davidson’s own branded oil, sold under the Screamin’ Eagle name for engine, primary, and transmission use in H-D motorcycles. Polaris has its own separate lineup of branded lubricants for its off-road and snowmobile vehicles.
Does switching to AMSOIL void my Harley warranty?
No. Under the Magnuson-Moss Warranty Act, a manufacturer cannot void your warranty simply for using a different oil brand, provided it meets the required specification and viscosity grade.
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AMSOIL and Harley-Davidson Screamin’ Eagle SYN3 are registered trademarks of their respective owners. Lube Oil Sales is an Authorized AMSOIL Independent Dealer (Dealer #1243776). This page contains affiliate links. SYN3 manufacturer and formulation details sourced from Harley-Davidson’s official published safety data sheets and product literature. AMSOIL specifications sourced from AMSOIL’s official product data. Last updated: July 2026.