MerCruiser 864539 Cooling Hose – Thermostat Housing to Starboard Manifold
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MerCruiser 864539 – Molded Cooling Hose | Thermostat Housing to Upper Starboard Manifold
Part Number: 864539 | Reference: 32-864539
Brand: Mercury Marine
Type: Molded Engine Cooling Hose
System: Closed Cooling
Position: Thermostat Housing to Upper Starboard Exhaust Manifold
GTIN: 745061554559
Genuine Mercury Marine replacement hose for the closed-cooling system on selected MerCruiser gasoline engines. This molded hose routes coolant between the thermostat housing and the upper starboard exhaust manifold, maintaining proper coolant flow through the engine's closed-loop system.
Compatible Applications
- 5.0L MPI Alpha / Bravo – through serial 0M614999 (starboard upper manifold position)
- 350 MAG MPI Alpha / Bravo – selected closed-cooling configurations
- Other V8 MerCruiser closed-cooling systems using the same upper starboard manifold hose arrangement
Serial Number Notice: Fitment depends on engine serial number and exhaust-riser configuration. On certain 5.0L MPI Alpha/Bravo engines this hose applies through serial 0M614999; later engines fitted with 3-inch or 6-inch warm risers require a different hose. Always verify against your engine serial number and cooling-system diagram before ordering.
When to Replace
Inspect this hose regularly and replace if you notice any of the following:
- Cracking, hardening, or surface checking
- Swelling or soft spots
- Chafing or damage near clamp areas
- Weeping, seeping, or active coolant leak at either connection
A deteriorating cooling hose can compromise the closed-cooling system and lead to coolant loss or overheating.
Installation Notes
- Allow the engine to cool completely before beginning any cooling-system work
- Note existing hose routing and clamp positions before removal
- Inspect thermostat-housing and exhaust-manifold connection points for corrosion or damage
- Install the replacement hose following the MerCruiser cooling-system layout
- Tighten hose clamps securely per MerCruiser service procedures
- Run the engine and inspect for leaks before returning to service
Part Numbers & Cross-Reference
- Mercury Marine: 864539
- Mercury Reference: 32-864539
- GTIN: 745061554559
Related Hoses
- Starboard riser hose: 864956
- Port-side non-riser hose: Mercury MerCruiser Quicksilver Cooling Hose — 32-864552
Parts Desk Insights
The defining characteristic of this hose is its upper starboard manifold position in the closed-cooling circuit. On otherwise identical MerCruiser engines, riser height and serial number range can change which hose is required — so always cross-check the cooling-system diagram for your specific engine configuration. Customers most commonly need this hose as part of a full cooling-hose inspection or replacement during an engine overhaul or after an overheating event. If you're replacing this hose, it's good practice to inspect the port-side counterpart (32-864552) and all other cooling hoses at the same time.
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.