AMSOIL 25W-40 Synthetic Blend Marine Engine Oil
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Engine Performance and Reliability for Fishing and Boating
Engine performance and reliability are key to a successful day fishing or boating. High-rpm operation and constant exposure to water, however, invite engine wear and formation of rust and corrosion. AMSOIL 25W-40 Synthetic Blend Marine Engine Oil guards against wear while delivering excellent protection against rust and corrosion. It is Warranty Secure and will not void your marine engine warranty.
Key Benefits
- Excellent high-stress, high-rpm endurance
- Increased rust and corrosion protection in humid, wet environments
- NMMA FC-W Catalyst Compatible — Registration FC-11825T
- Designed with excellent shear stability for a consistent lubricating film
- Engineered for the ~5,000 rpm marine duty cycle versus the ~2,000 rpm automotive duty cycle
- API SM service category
- Doubles OEM drain interval in inboard / I/O applications (up to one year)
- Warranty Secure — keeps factory marine engine warranty intact
Shear Stability, Rust Protection, NMMA Certification
Protects against wear: On average, a marine engine powering a boat 30 mph runs at about 5,000 rpm — versus an automotive engine powering a car 60 mph at about 2,000 rpm. Higher stress causes traditional automotive oils to break down and lose viscosity. AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is designed with excellent shear stability to deliver a consistent lubricating film.
Excellent anti-rust performance: Marine engines are prone to rust and corrosion due to constant exposure to humid, wet environments. Rust on engine parts acts like sandpaper, scouring bearings, the cylinder wall and piston rings, while aluminum parts can corrode. AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is fortified with potent inhibitors that guard against damaging rust and corrosion.
NMMA certified: Certified by the National Marine Manufacturers Association (NMMA) for use in four-stroke outboards, inboards, stern-drives (inboard/outboards) and PWC. Exceeds the NMMA FC-W (Four Cycle – Water) specification requirements. FC-W (CAT) Registration: FC-11825T.
Technical Specifications
| Property | Value |
|---|---|
| Kinematic Viscosity @ 100°C, cSt | 16.0 |
| Kinematic Viscosity @ 40°C, cSt | 139.3 |
| Viscosity Index | 121 |
| Flash Point | 254°C (489°F) |
| Fire Point | 284°C (543°F) |
| Pour Point | -31°C (-24°F) |
| NOACK Volatility, % weight loss | 3.1 |
| HTHS Viscosity @ 150°C, cP | 4.8 |
| Total Base Number | 7.9 |
| Four-Ball Wear Test (40 kg, 150°C, 1800 rpm, 1 hr), Scar, mm | 0.40 |
Industry Certifications & OEM Approvals
NMMA
- FC-W Catalyst Compatible (Registration FC-11825T)
API
- SM
Applications
Use in gasoline-fueled four-stroke inboards, outboards, inboard/outboards and personal watercraft, including those made by Mercury and Mercruiser. Meets API SM and NMMA FC-W Catalyst Compatible.
Pros and Cons
Pros
- Excellent high-stress, high-rpm endurance
- Increased rust and corrosion protection in humid, wet environments
- NMMA FC-W Catalyst Compatible — Registration FC-11825T
- Designed with excellent shear stability for a consistent lubricating film
- Engineered for the ~5,000 rpm marine duty cycle versus the ~2,000 rpm automotive duty cycle
- API SM service category
- Doubles OEM drain interval in inboard / I/O applications (up to one year)
- Warranty Secure — keeps factory marine engine warranty intact
Cons
- Premium Investment: Higher initial cost compared to conventional or "shelf-brand" synthetic oils.
- Limited Local Retail: Primarily available through authorized dealers and specialized synthetic outlets. National Synthetics is a local stocking dealer. Call 1-678-944-8816 to confirm in-stock items for same-day local pickup.
Order Through Your Independent AMSOIL Dealer
Get the right blend of performance and value for your boat. As your Independent AMSOIL Dealer, we provide expert guidance and competitive pricing on all AMSOIL products.
Independent AMSOIL Dealer #1858536
Shipping & Returns
Fast, Reliable Shipping
- Free standard ground shipping on orders of $100 ($130 in Canada) or more.
- Orders under the threshold ship for a flat $9.99 ($12.99 in Canada) freight charge.
- In-stock items typically delivered in two to three business days.
- U.S. and Canada only — no shipments to PO Boxes.
30-Day Return Policy
- Return unopened, currently marketed products within 30 days for a full refund (minus freight).
- Exchange unopened products within 90 days with no restocking fee.
- Special-order items are non-returnable.
- Returns are handled directly by AMSOIL.
Frequently Asked Questions
On average, a marine engine powering a boat 30 mph runs at about 5,000 rpm. In contrast, an automotive engine powering a car 60 mph runs at about 2,000 rpm. Higher stress and constant water exposure cause traditional automotive oils to break down, lose viscosity and leave engines vulnerable to rust and corrosion. AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is engineered for the marine duty cycle.
Yes — AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is certified by the NMMA for use in four-stroke outboards, inboards, stern-drives and PWC, and exceeds the NMMA FC-W specification. FC-W (CAT) Registration Number: FC-11825T.
No. AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is Warranty Secure, keeping your factory warranty intact. It is a high-performance replacement for vehicle-manufacturer-branded products and is backed by the AMSOIL Limited Warranty.
In four-stroke outboards and personal watercraft, change oil at the engine or watercraft manufacturer-recommended interval due to potential fuel dilution and water contamination. In inboard and inboard/outboard applications, change at two times the engine manufacturer-recommended interval or once a year, whichever comes first.
Customer Reviews
See all 37 reviewsGreat product. Boat runs well using it.
This is what my mechanic uses for my tune fluid changes. I’m going to start using this for my Hummers as well.
Verified customer review via AMSOIL.com.
Outstanding product
This oil immediately cured the low oil pressure problem in my outboard. Motor sounds great, runs great. The lower end also performs well with the 75-90 Marine Amsoil gear lube. I run Amsoil in every motor I own including those in my cars from the forties and fifties and I have for decades. Great stuff.
Verified customer review via AMSOIL.com.
Independent AMSOIL Dealer #1858536. Product information sourced from AMSOIL. Visit AMSOIL.com for the most current product details and availability.