Mercury 4-Stroke Marine Engine Oil – 25W-40, 4L | Part 8M0078640

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

About This Oil

This is the OEM-specified SAE 25W-40 4-stroke crankcase oil for Mercury FourStroke outboards and MerCruiser sterndrive engines, sold in a 4-litre container. The 25W-40 grade is the standard viscosity for the majority of Mercury and MerCruiser 4-stroke engines. The synthetic blend formula delivers superior wear protection, corrosion resistance, and viscosity stability under the sustained high-RPM and high-load conditions of marine use. NMMA FC-W and FC-W Catalyst Compatible certified — safe for catalytic converter-equipped engines. The 4L size covers most single-engine outboard or sterndrive oil changes in a single jug.

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 2.5–4L per change; larger MerCruiser sterndrives may require more — confirm your engine’s capacity in the service manual.

Technical FAQ

Q: How does this differ from the 1L version (8M0078639)?
A: Same oil, larger container. The 4L jug covers most single-engine oil changes in one bottle and is more economical per litre. The 1L (8M0078639) is better for top-ups or small-displacement engines.

Q: Can I use automotive 25W-40 instead?
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: What if my engine specifies 10W-30 or 25W-50?
A: Use the viscosity specified in your owner’s manual. For 10W-30 see our Mercury 4-Stroke Engine Oil – 10W-30, 4L (8M0078638). For 25W-50 high-performance applications see the Mercury 25W-50 High Performance Oil (8M0078013).

Q: Is this FC-W Catalyst Compatible?
A: Yes — safe for use in engines equipped with catalytic converters.

Q: Is there a higher-spec synthetic blend version?
A: Yes. See the Mercury 4-Stroke Synthetic Blend Engine Oil – 25W-40, 4L (8M0078642) for a higher-spec synthetic blend option.

Related Parts

• Mercury 4-Stroke Marine Engine Oil – 25W-40, 1L (8M0078639) — smaller size for top-ups
• Mercury 4-Stroke Engine Oil – 10W-30, 1L (8M0078637)
• Mercury 4-Stroke Engine Oil – 10W-30, 4L (8M0078638)
• Mercury 4-Stroke Synthetic Blend Engine Oil – 25W-40, 4L (8M0078642)
• 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 – 1.7L 75–115 HP EFI FourStroke (8M0081917)
• Mercury Quicksilver 100-Hour Service Kit (8M0094232)
• Mercury Quicksilver 100-Hour Service Kit (8M0097854)
• Browse all Mercury MerCruiser Engine Maintenance Parts

Parts Desk Insights

Best use case: Full scheduled oil changes on Mercury 4-stroke outboards and MerCruiser sterndrives that specify 25W-40 — the most common viscosity across Mercury’s 4-stroke lineup. The 4L jug is the right buy for most single-engine services: most Mercury 4-stroke outboards take 2.5–4L per change, so one jug typically covers a complete service with minimal waste. Also the economical choice for twin-engine boats or anyone servicing multiple engines in a season.

Common mistakes: The most frequent error is substituting 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 specifies 10W-30 (common on smaller-displacement or newer Mercury outboards) or 25W-50 (high-performance applications) — 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 that leads to an incomplete service.