Mercury MerCruiser 864579 Cooling System Hose – Check Valve to Thermostat Housing
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Mercury MerCruiser 864579 – Cooling System Hose
Part Number: 864579 / 32-864579
Brand: Mercury / MerCruiser
Type: Molded cooling-system hose
Position: Check valve to thermostat housing
GTIN: 745061545793
Overview
This is a genuine Mercury MerCruiser cooling-system hose that connects the check valve to the thermostat housing on selected MerCruiser gasoline inboard and sterndrive engines. It is a direct-fit molded replacement that follows the original routing and connection geometry for the engines listed below.
Key Features
- Genuine Mercury / MerCruiser OEM replacement part
- Molded hose designed to match the original routing and connection points exactly
- Connects the check valve to the thermostat housing in the standard cooling circuit
- Built for the demands of closed-cooled and raw-water marine cooling systems
Compatible Applications
- MerCruiser 4.3L MPI Alpha / Bravo
- MerCruiser 5.0L MPI Alpha / Bravo
- MerCruiser 350 MAG MPI 5.7L Alpha / Bravo
- MerCruiser 350 MAG MPI Horizon
- MerCruiser 377 MAG MPI
- MerCruiser MX 6.2L MPI
- Selected 357 / 383 MAG Stroker configurations
- Serial number fitment notice: Cooling-system hose layouts vary by engine model, serial range, drain system, and Alpha/Bravo configuration. Always confirm the engine serial number and verify part number 864579 / 32-864579 in the applicable cooling-system diagram before ordering.
System & Diagram Position
Parts diagrams identify 864579 within the standard cooling system assembly, specifically on 5.0L MPI, 350 MAG MPI, and MX 6.2L MPI engines. It occupies the position between the check valve outlet and the thermostat-housing inlet — a critical junction that routes coolant through the thermostat circuit.
When to Replace
Replace this hose if it is cracked, hardened, swollen, soft, chafed, or shows any damage at the connection points. Aging cooling hoses can develop leaks or internal restrictions that disrupt proper coolant circulation and engine temperature control — even a small leak at this location can affect thermostat function.
Installation Notes
- Allow the engine to cool completely before beginning any cooling-system service
- Note the original hose routing and clamp positions before removing the old hose
- Inspect the check valve, thermostat housing fitting, and existing clamps while the hose is off
- Install the new hose and tighten clamps to the torque specified in the engine service manual
- Run the engine and inspect carefully for leaks at both connection points before returning the vessel to service
Cross-Reference / Alternate Part Numbers
- Mercury / MerCruiser: 864579
- Mercury catalog reference: 32-864579
- Search reference: 32864579
- GTIN: 745061545793
Dimensions & Weight
- Weight: approx. 200 g (0.44 lb) — best estimate for a molded marine cooling hose of this type
- Refer to the MerCruiser parts diagram for exact hose routing dimensions
Parts Desk Insights
Best Use Case: This hose is the right part when a cooling-system inspection on a MerCruiser V6 or V8 MPI engine reveals a failed or degraded hose at the check valve-to-thermostat housing junction. It's a common service item on higher-hour engines and a worthwhile replacement during any thermostat or raw-water pump service.
Common Issues: The most important step is confirming position in the diagram before ordering — nearby MerCruiser hoses can look nearly identical but connect different components. Match by part number (864579 / 32-864579) and engine serial number, not by appearance alone. If the thermostat housing or check valve fittings show corrosion or damage, plan to address those at the same time to avoid a repeat repair.
Related Products
- Mercury MerCruiser 3.0L Drain System Adapter Assembly – 22-862605T1 — related MerCruiser cooling/drain system component
- Mercury Water Distributor Thermostat Housing Gasket – 27-475901 — replace the thermostat housing gasket while servicing this area
- Mercury Cooling Hose – 160211 — companion cooling hose for MerCruiser applications
- Mercury Quicksilver Extended Life Coolant/Antifreeze 877770K1 — top up coolant when servicing the cooling system
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:
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