AMSOIL vs Yamalube
Yamalube is Yamaha’s OEM-branded oil for motorcycles, ATVs, and outboards. Here’s what a real ASTM-tested lab study found when it compared Yamalube 4-R directly against AMSOIL, plus current official specs for what’s sold under the Yamalube name today.
Alan Williams · AMSOIL Direct Jobber #1243776 · Tomball, TX · 225-441-6397
AMSOIL’s ASTM-Tested Study, With Two Honest Caveats
What “A Study of Motorcycle Oils” Actually Found
AMSOIL’s Power Sports Group published a lab study testing 16 SAE 50-grade motorcycle oils, including Yamalube 4-R and AMSOIL MCV, across 12 separate ASTM test methods, with a notarized affidavit certifying compliance with ASTM methodology. Two things worth knowing before the numbers: this is AMSOIL’s own commissioned study, not an independent third-party test, and it dates to 2006 (revised 2008), testing Yamalube 4-R, which the study itself lists as a semi-synthetic (petroleum/synthetic blend), not Yamaha’s current full-synthetic Hi-Performance or GP Racing Spec oils.
| Test (ASTM Method) | AMSOIL MCV 20W-50 | Yamalube 4-R 10W-50 |
|---|---|---|
| Shear stability (D-6278) | Held within its 50-weight grade | Sheared down out of grade to a 40-weight |
| Gear wear, FZG (D-5182) | Passed stage 13 (maximum), 0 mm wear | Failed with 226 mm of wear |
| TBN, acid neutralization (D-2896) | 11.06 | 9.74 |
| Overall study ranking (of 16 oils tested) | Ranked 1st, total score 31 | Ranked 13th (tied), total score 89 |
One point the study itself calls out: Yamalube 4-R had one of the highest viscosity index ratings in its group, meaning it resisted temperature-related thinning well, but it also showed one of the largest shear-related viscosity drops of any oil tested, illustrating that viscosity index and shear stability measure different things, and a strong showing in one doesn’t guarantee a strong showing in the other.
Riding a Yamaha motorcycle, ATV, or running an outboard? Tell me the model and I’ll confirm the right AMSOIL grade, no upsell.
What’s Sold Under the Yamalube Name Today
Current Official Specifications
Yamaha has since introduced true full-synthetic Yamalube products, a different tier than the semi-synthetic 4-R tested above. Here’s what each brand currently publishes.
| Spec | AMSOIL Motorcycle Oils | Yamalube Hi-Performance / GP Racing Spec |
|---|---|---|
| Base stock | Full synthetic | Full synthetic (current formulations) |
| JASO rating | MA, wet-clutch compatible formulas available | Hi-Performance is JASO MA, GP Racing Spec is JASO MA2 |
| API rating | Meets or exceeds current API requirements | API SL |
| Viscosity range available | 0W through 20W-50, application-specific formulas | 10W-40, both current full synthetic grades |
No independent third-party test comparing AMSOIL’s current motorcycle oils to Yamalube’s current full-synthetic Hi-Performance or GP Racing Spec formulas is publicly available. The ASTM study above remains the most rigorous data point found, applied to the earlier semi-synthetic Yamalube 4-R.
Get AMSOIL’s full synthetic motorcycle oil at 25% off as a Preferred Customer.
Where Yamalube Is a Reasonable Choice
Yamalube is a legitimate, purpose-built oil, and there are real reasons to stick with it:
- Riders enrolled in Yamaha’s “Yamalube Advantage” extended engine warranty program, which can offer up to 20 years or 100,000 miles of coverage on qualifying vehicles when Yamalube is used consistently, a separate program from the standard factory warranty, and one tied specifically to using Yamalube
- Riders who prefer picking up oil and parts in one dealer visit
- New engines still being broken in, where some riders prefer to stay on OEM-spec oil through the initial service interval
Common Questions
Is Yamalube full synthetic?
It depends which product. Yamaha sells mineral, semi-synthetic, and full synthetic Yamalube oils. The current Hi-Performance and GP Racing Spec lines are full synthetic; older or lower-tier Yamalube products, including the 4-R tested in the ASTM study above, are semi-synthetic blends. Check the bottle for “full synthetic” labeling before assuming.
Does switching to AMSOIL void my Yamaha warranty?
Your standard factory 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. However, if you’re enrolled in the separate Yamalube Advantage extended warranty program, that program’s terms are specifically tied to continued Yamalube use, so switching oils could affect that particular coverage. Check your Yamalube Advantage enrollment terms directly before switching if you’re relying on that program.
Is AMSOIL safe for a wet clutch?
Yes, when you use AMSOIL’s JASO MA-rated motorcycle oils. AMSOIL offers wet-clutch compatible formulas free of the friction modifiers that can cause clutch slippage, matching Yamalube’s own JASO MA/MA2 approach.
Which AMSOIL oil replaces Yamalube in my Yamaha?
Match the viscosity grade your Yamaha calls for, typically 10W-40, and choose the AMSOIL motorcycle oil rated for your engine type (street, off-road, or ATV/UTV). Call or send your exact model and I’ll confirm the correct grade.
Get the Right Oil for Your Yamaha
Call and tell me your model and how you ride it, and I’ll tell you the exact AMSOIL grade, straight, no upsell.
More Comparisons & Guides
AMSOIL and Yamalube are registered trademarks of their respective owners. Lube Oil Sales is an Authorized AMSOIL Independent Dealer (Dealer #1243776). This page contains affiliate links. ASTM lab study data as published by AMSOIL Power Sports Group, 2006, revised 2008, testing Yamalube 4-R, a semi-synthetic blend. Current Yamalube specifications sourced from Yamaha Motor Corporation product announcements and official retailer listings. AMSOIL specifications sourced from AMSOIL’s official product data. Last updated: July 2026.