Mercury 4-Stroke Marine Engine Oil – 25W-40, 1L | Part 8M0078639

Mercury 4-Stroke Marine Engine Oil – 25W-40 | 1 Litre

About This Oil

This is the OEM-specified SAE 25W-40 4-stroke crankcase oil for Mercury FourStroke outboards and MerCruiser sterndrive engines — the standard viscosity for the majority of Mercury and MerCruiser 4-stroke engines. Its marine-specific synthetic blend additive package delivers corrosion resistance, shear stability, and wear protection under the sustained high-RPM and high-load conditions of marine use. NMMA FC-W and FC-W Catalyst Compatible certified, making it safe for catalytic converter-equipped engines. Sold in a 1-litre container.

Compatible Applications

• Mercury FourStroke outboards 2.5 HP – 400 HP requiring 25W-40 crankcase oil
• Mercury Pro XS FourStroke outboards
• Mercury Verado FourStroke outboards
• MerCruiser 3.0L, 4.3L V6, 5.0L V8, 5.7L V8, 6.2L V8, 7.4L V8, and 8.2L V8 sterndrive and inboard engines
• Any 4-stroke marine engine where SAE 25W-40 is specified
• Always verify the recommended viscosity in your engine owner’s manual and against your serial number range before ordering

Service Interval

Change engine oil and filter every 100 hours or annually, whichever comes first — per the Mercury and MerCruiser service manual. Always replace the oil filter at each oil change. Do not extend intervals in saltwater or high-hour applications. Most Mercury 4-stroke outboards require 1.5–2.5 litres per change; larger MerCruiser sterndrives typically require 4–5 litres — confirm your engine’s capacity in the service manual.

Technical FAQ

Q: Can I use automotive 25W-40 instead of this marine oil?
A: No. Automotive oils lack the marine-specific corrosion inhibitors and FC-W certification required for boat engines. Using automotive oil can void your warranty and accelerate internal corrosion, particularly in engines that sit with moisture exposure between uses.

Q: My engine calls for 25W-40 — is this the right oil?
A: Yes, for most Mercury and MerCruiser 4-stroke engines. Confirm in your owner’s manual — some newer models specify 10W-30 or 25W-50 instead.

Q: How much oil does my engine take?
A: Capacity varies by engine. Refer to your owner’s manual for the correct fill volume and always check the dipstick after filling. For most full oil changes, the 4L size (8M0078640) is more economical than multiple 1L bottles.

Q: What’s the difference between this and the 10W-30 version?
A: Viscosity grade. Most Mercury and MerCruiser 4-stroke engines specify 25W-40; some smaller-displacement or newer models specify 10W-30. Always follow your engine’s service manual. See our Mercury 4-Stroke Engine Oil – 10W-30, 1L (8M0078637) if your engine requires 10W-30.

Q: Is there a higher-performance option?
A: Yes. For high-performance or racing applications, see the Mercury 4-Stroke High Performance Engine Oil – 25W-50, 1 Qt (8M0078013).

Related Parts

• Mercury 4-Stroke Marine Engine Oil – 25W-40, 4L (8M0078640) — larger size for full oil changes
• Mercury 4-Stroke Engine Oil – 10W-30, 1L (8M0078637) — for engines specifying 10W-30
• Mercury 4-Stroke Engine Oil – 10W-30, 4L (8M0078638)
• Mercury 4-Stroke High Performance Engine Oil – 25W-50, 1 Qt (8M0078013)
• Mercury Quicksilver Oil Filter 877761K01 – 75–150 HP FourStroke
• Mercury Quicksilver Oil Filter 877769K01 – L6 Verado Outboard
• Mercury MerCruiser Quicksilver Oil Filter 822626Q15
• Mercury MerCruiser Quicksilver Oil Filter Wrench 802653K02
• Mercury Oil Change Kit – 15 & 20 HP Carbureted FourStroke (8M0081914)
• Browse all Mercury MerCruiser Engine Maintenance Parts

Parts Desk Insights

Best use case: Routine scheduled oil changes on Mercury 4-stroke outboards and MerCruiser sterndrives that specify 25W-40 — which covers the majority of Mercury’s 4-stroke lineup. This is the go-to viscosity for most Mercury marine engines. The 1L size is best for topping up between changes or for smaller engines with low oil capacity; for a full change on most outboards or sterndrives, the 4L (8M0078640) is more economical.

Common mistakes: The most frequent error is using an automotive 25W-40 because the viscosity matches — marine engines require FC-W certified oil with a corrosion inhibitor package that automotive oils don’t include. Customers also sometimes order 25W-40 when their engine actually specifies 10W-30 (common on smaller-displacement or newer Mercury outboards) — always check the owner’s manual first. Always replace the oil filter at the same time; ordering oil without a filter is a common oversight.