Mercruiser 4-Stroke Synthetic Oil 4L - OEM Part 8M0078642
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Mercury 8M0078642 is a genuine OEM 4-stroke synthetic blend marine engine oil in a 4-litre container. Dealer listings identify it as OIL 4S SYN4L, and Mercury's current marine-oil lineup positions its 4-stroke synthetic blend oils as marine-specific lubricants built for corrosion protection, wear resistance, and viscosity retention in marine engines.
Key Features
- Genuine Mercury Marine / Quicksilver OEM oil
- Part number 8M0078642
- 4-litre container
- 4-stroke synthetic blend marine engine oil
- Mercury says its 4-stroke marine oils are engineered for strong lubrication, corrosion prevention, and long-term durability in marine applications.
Engine Compatibility
This oil belongs to Mercury's 25W-40 synthetic blend 4-stroke marine engine oil family, which Mercury describes for outboard, sterndrive, and inboard 4-stroke marine engines. Exact oil selection should still be confirmed by the engine owner's manual and serial-number-based parts lookup before purchase.
Serial Number Fitment Notice
Please confirm the correct oil specification using your exact Mercury or MerCruiser model and serial number in the Mercury Parts Catalog before purchase. Mercury's catalog is organized by model and serial number for accurate application matching.
When This Part Needs Replacement
Use this oil during routine engine oil changes on applicable 4-stroke marine engines. Fresh marine-grade oil helps protect internal components against friction, corrosion, and viscosity breakdown under marine load and storage conditions. That service guidance is consistent with Mercury's description of its 4-stroke marine oils.
Installation Notes
Use only the oil viscosity and formulation specified for the engine being serviced. Mercury's 4-stroke synthetic blend oils are marine-specific products, so matching the exact oil grade to the engine manual is the safest approach.
Alternate / Superseded Part Numbers
- 8M0078642
- Supersedes 858053KC1 according to dealer supersession listings.
Parts Desk Insight
Marine engine oil is not just about viscosity. The additive package matters too, especially for corrosion protection and maintaining film strength in engines that see humidity, storage time, and sustained load. That is why Mercury positions its 4-stroke oils separately from automotive oils.
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.