Milwaukee-Eight
2021 Harley-Davidson FLHX Street Glide Oil
AMSOIL synthetic oil recommendations for the 2021 FLHX Street Glide.
Why AMSOIL Is the Best Synthetic Oil for the 2021 FLHX Street Glide
This guide covers the 2021 Harley-Davidson FLHX Street Glide specifically. AMSOIL synthetic oil recommendations match the engine code, displacement, and oil capacity that shipped on this exact variant, so you order the right viscosity and the right number of quarts the first time.
Modern Milwaukee-Eight platform engines run hotter and shear oil faster than the Twin Cam motors they replaced. AMSOIL synthetic motorcycle oil is engineered for exactly that kind of duty cycle.
In CEC L45-KRL shear-stability testing (ASTM D445), AMSOIL 20W-50 V-Twin Synthetic resists viscosity breakdown 6X better than Harley-Davidson Screamin' Eagle SYN3. For Milwaukee-Eight owners who tour, ride two-up, or sit in long stretches of hot rally traffic, that shear-stability gap is measurable in oil pressure, gear protection, and clutch feel.
Frequently Asked Questions
How much oil does a 2021 Street Glide take?
The 2021 Harley-Davidson FLHX Street Glide holds approximately 4 quarts of engine oil with a filter change. Always confirm via the owner's manual and check the level on the dipstick after refill.
What is the best oil for a Street Glide?
AMSOIL 20W-50 100% Synthetic V-Twin Motorcycle Oil is the recommended choice for the 2021 Street Glide. It outperforms Harley-Davidson Screamin' Eagle SYN3 by 6X in independent shear-stability testing and protects the integrated transmission and primary in the same drain interval.
How do I change the oil on a Street Glide?
Warm the engine for 5 minutes, drain the engine sump via the lower drain plug, replace the oil filter (AMSOIL Ea Motorcycle Filter), refill with the manufacturer-specified amount of AMSOIL 20W-50 V-Twin Synthetic, then run the engine for 30 seconds, let it sit 5 minutes, and check the level via the dipstick with the bike upright on a level surface.
What is the oil change interval for a 2021 Street Glide?
Harley-Davidson recommends 5,000-mile engine oil change intervals with conventional oil. AMSOIL synthetic V-twin oil's superior shear stability and oxidation resistance lets you confidently follow that interval, or use AMSOIL's extended-drain guidance for severe service. Transmission and primary fluids are typically changed at every second and third engine oil change respectively.
How often should I change the primary fluid in a Street Glide?
AMSOIL recommends changing the primary chaincase fluid every third engine oil change. The Street Glide's clutch pack runs in the same fluid, and AMSOIL synthetic primary fluid maintains consistent friction characteristics for smoother clutch engagement throughout the interval.
