Mercury MerCruiser Quicksilver Cooling Hose 864578 — Drain Fitting to Check Valve
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
Mercury MerCruiser Quicksilver Cooling Hose — OEM Part 864578
This genuine OEM cooling hose connects the drain fitting to the check valve in MerCruiser's raw-water cooling and drain system. Engineered to Mercury Marine factory specification, it maintains the correct routing, sealing, and flow path that MerCruiser's cooling circuit depends on. If your hose is cracked, hardened, swollen, or weeping at either end, this is the correct OEM replacement — position-specific and direct-fit.
Part Information
- OEM Part Number: 864578
- Mercury Reference: 32-864578
- Brand: Mercury / Quicksilver
- Official Product Type: Cooling-system hose
- System: Raw-water / standard cooling and drain system
- Diagram Position: Drain fitting to check valve
- GTIN / UPC: 745061545786
Compatible Applications
- MerCruiser 5.0L MPI Alpha / Bravo — 5.0L (305 cu. in.) V8 GM engine family with Alpha 7-point drain cooling system
- Selected MerCruiser gasoline inboard and sterndrive engines using the standard raw-water cooling and drain layout
- Confirm fitment via engine serial number and cooling-system diagram before ordering — MerCruiser used multiple hose layouts depending on engine family, drive configuration, and drain-system design
Related Parts
- Mercury MerCruiser 864579 — Check Valve to Thermostat Housing Hose (adjacent hose in the same cooling diagram)
When to Replace
- Hose is cracked, hardened, or swollen
- Chafing or wear visible near the fittings
- Leaking or seeping at either connection point
- Hose shows internal restriction or collapses under suction
- Part of a scheduled cooling-system service or pre-season inspection
Installation Notes
- Allow the engine to cool fully before beginning service
- Note the existing hose routing and clamp positions before removal
- Inspect the drain fitting, check valve, and hose clamps while the hose is off
- Verify the cooling system is leak-free after installation before returning the engine to service
Service Interval
Inspect annually as part of spring commissioning. Replace at the first sign of cracking, hardening, or seepage — or proactively every 3–5 years as part of a full cooling-system hose refresh.
Technical FAQ
What is the difference between 864578 and 864579?
These two hoses appear side-by-side in the same MerCruiser cooling diagram but serve different connections. 864578 runs from the drain fitting to the check valve; 864579 continues from the check valve to the thermostat housing. They are not interchangeable.
How do I confirm this hose fits my engine?
Match OEM part number 864578 to your engine serial number using the Mercury parts diagram for your specific engine family and drive configuration. Cooling hose layouts vary between model years and drain-system designs.
Parts Desk Insights
This hose is most often needed during spring commissioning or after winterization, when cooling hoses are inspected for hardening or cracking from thermal cycling. The most common customer mistake is ordering 864579 instead — the two hoses sit next to each other in the diagram and are easy to confuse. When replacing 864578, it’s worth checking 864579 at the same time, since both hoses age at the same rate. Browse the full Mercury MerCruiser Cooling System Parts collection for clamps, check valves, thermostats, and water pumps.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 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.