Upgrade from OEM – 25W-40 Synthetic Blend Marine Engine Oil

25W-40 Synthetic Blend Marine Engine Oil25W-40 WCM Protects Against Wear
Marine engines operate under high loads and rpm for extended periods. 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 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. It helps guard engine components from wear for maximum life.

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Call 800-579-0580 for competitive current price.
Or use the online preferred customer portal if you choose to order online.

Printable Product Data Sheet for 25W-40 Synthetic Blend Marine Engine Oil.

Vehicle Look-up: Match AMSOIL Products to your model

Marine 25W-40 Provides 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, piston rings and other components, while aluminum pistons and other parts can corrode. Rust and corrosion reduce engine power and eventually cause catastrophic failure.

Good rust protection is not natural to motor oil; it comes only by design. AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is fortified with potent inhibitors that guard against damaging rust and corrosion.

  • Excellent high-stress, high-rpm endurance
  • Increased rust and corrosion protection

NMMA Certified

AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is certified by the National Marine Manufacturers Association (NMMA) for use in four-stroke outboards, inboards, stern-drives (inboard/outboards) and PWC. This high-quality oil demonstrates outstanding performance and exceeds the NMMA “FC-W” (Four Cycle – Water) specification requirements.

  • FC-W (CAT)® Registration Number: FC-11825T

* All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are AMSOIL-engineered for use in the applications shown.

APPLICATIONS of the 25W-40

Use in gasoline-fueled four-stroke inboards, outboards, inboard/outboards and personal watercraft that require any of the specifications listed below, including those made by Mercury and Mercruiser.

  • API SM
  • NMMA FC-W Catalyst Compatible

Many of our customers are already using our 10W-40 WCF in these engines. If you like the added performance of it there’s no reason to change.

Marine Oil Service Life

Four-stroke outboard motors and personal watercraft: Due to potential fuel dilution or water contamination, change oil at the engine or watercraft manufacturer-recommended interval. Inboard and I/O applications: Change oil at two times the engine manufacturer-recommended interval, or once a year, whichever comes first.

Your Mercury Warranty is Secure with AMSOIL Marine Oils

AMSOIL 25W-40 Synthetic Blend Marine Engine Oil is Warranty Secure®, keeping your factory warranty intact.  For details, visit www.amsoil.com/warrantysecure.

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, reducing engine performance and life. 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’s warranty.

warranty safe

Protected from Warranty constraints

Maybe you’ve heard of motorcycle, UTV, snowmobile or other dealerships pressuring people into buying the manufacturer’s brand of parts or lubricants to avoid losing their factory warranty. If it’s happened to you, it probably left a bad taste in your mouth.

That’s because no one likes to be told what to buy. And no one likes to be taken advantage of.


In America, the federal Magnuson Moss Warranty Act protects your freedom to choose the brand of parts and lubricants you think is best. It also protects your right to extend oil-change intervals beyond what’s given in your owner’s manual without fear of voiding your factory warranty.

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Marine 4-stroke Reviews


By  ALEX,  a  Verified Buyer  from  B.C.   on  May 24, 2023

Originally I was using too light of an oil and I went to this 25W40 and was very happy with the oil pressure increase and now it doesn’t seem to go through any oil. Big block Chevy

BEEN USING THIS 25W-40 SINCE it has been offered

By  MICHAEL,  a  Verified Buyer  from  Long Island NY.   on  March 09, 2023

Great Oil. Have used it on my 1998 7.4 MPI Bravo 3 since it was first offered. Very little oil consumption. No smoke; engine have been running great with good oil pressure at idle at operating temperature.

Best you can get

By  ERIC,  a  Verified Buyer  from  Vermont  on  August 16, 2022

I trust all of Amsoil products and I am using this in my Mercuriser IO cheaper than Quicksilver and I’m sure its a much better oil.

8.1 mercruiser – 1300 hrs

By  CHRISTOPHER,  a  Verified Buyer  from  Tampa   on  October 22, 2021

Best oil marina oil on the market. Using oem oil my engines would burn oil every trip . Changed to amsoil instantly stopped consuming oil. Also holds better oil pressure.

Marine Oil

By  BRIAN,  a  Verified Buyer  from  Granum Alberta  on  April 14, 2022

My 150 Merc runs smooth and and cool



This product is not expected to cause health concerns when used for the intended application and according to the recommendations in the Safety Data Sheet (SDS). And SDS is available via the Internet at www.amsoil.com or upon request at (715) 392-7101. Keep Out of Reach of Children. Recycle used oil and bottle.