Sierra 18-70939 Molded Cooling Hose - Mercruiser 32-8066361 - Thermostat Housing to Starboard Exhaust Manifold, GM V-6/V-8 305/350

The Sierra 18-70939 is a molded cooling system hose engineered for fresh water or raw water cooling systems on MCM/MIE GM V-6 and V-8 (305 and 350 cid) sterndrive engines. It is designed to route coolant from the thermostat housing to the starboard exhaust manifold, and its molded construction maintains full, unrestricted water flow through the bend rather than relying on a flexible section that can kink or collapse under vacuum.

Construction is EPDM tubing with a synthetic knit reinforcement layer, giving the hose the heat and chemical resistance needed for continuous exposure to engine coolant while resisting collapse, cracking, and age-hardening. Because it is molded to the exact bend and length required for this application, installation matches the original routing without needing to force, clamp-bend, or trim a straight length of hose. Sierra engineers this hose to OEM quality so that fit, form, and function match the factory original.

This hose is specific to the starboard side application; it is not interchangeable with a port-side routing hose, which would carry a different part number. Confirm your engine is an MCM/MIE GM V-6 or V-8 (305 or 350 cid) application before ordering to ensure correct fit.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-70939
• Material: EPDM tubing with synthetic knit reinforcement
• Color: White
• Weight: 0.64 pounds
• Application: Thermostat housing to starboard exhaust manifold
• Side: Starboard
• Engine Fitment: MCM/MIE GM V-6 & V-8 (305 & 350 cid) engines
• Mercruiser Cross Reference: 32-8066361
• UPC: 808282227685

Fitment

• MCM/MIE GM V-6 & V-8 (305 & 350 cid) engines

Replaces (OEM)

• 32-8066361

Frequently Asked Questions

What engines does the Sierra 18-70939 molded hose fit? The Sierra 18-70939 fits MCM/MIE GM V-6 and V-8 (305 and 350 cid) engines.

Where does this hose route on the engine? It routes from the thermostat housing to the starboard exhaust manifold, so it is intended for the starboard side of the engine.

Will the 18-70939 work on the port side instead? No. This hose is molded specifically for the starboard exhaust manifold routing; a port-side hose is a separate part with a different part number, so make sure you are ordering for the correct side.

Is there an OEM Mercruiser number for the 18-70939? Yes, the Sierra 18-70939 cross-references to Mercruiser part number 32-8066361.

What material is the hose made from? The 18-70939 uses EPDM tubing with a synthetic knit reinforcement layer, giving it heat and chemical resistance for continuous coolant exposure.

How much does this hose weigh? The Sierra 18-70939 molded hose weighs 0.64 pounds.

What color is the 18-70939 hose? It is white.

Is this a straight length of hose or pre-shaped? The 18-70939 is molded to the specific bend of the thermostat-housing-to-exhaust-manifold routing, providing full water flow through the bend rather than requiring a flexible hose to be forced into shape.

Is the Sierra 18-70939 built to OEM quality? Yes, Sierra molded hoses including the 18-70939 are designed to be OEM quality and correct in fit, form, and function for the original routing.

Can this hose be used in a raw water cooling system? Yes, the 18-70939 molded hose is designed for both fresh water and raw water cooling systems on the applicable MCM/MIE GM V-6/V-8 engines.

Does the 18-70939 come with a warranty? Yes, this Sierra molded hose is covered under Sierra's customer satisfaction warranty.

How do I confirm the 18-70939 is the right hose for my boat? Verify your engine is an MCM/MIE GM V-6 or V-8 in 305 or 350 cid, and that you need the thermostat-housing-to-starboard-exhaust-manifold hose, before ordering part 18-70939.