Sierra Molded Hose 18-70943, OEM 32-89749-1, Thermostat Housing to Port Exhaust Manifold, Mercruiser GM V-8 454/502 cid

The Sierra 18-70943 is a molded rubber hose engineered for Mercruiser MCM/MIE GM V-8 (454 & 502 cid) engines, including the 74L, 454 Mag, and 502 Mag applications. This hose is designed to connect the thermostat housing to the port exhaust manifold, routing coolant through this critical section of the cooling system. Because it is molded to the specific bend and length required for this connection, it seats correctly without the kinking or stress that a straight-cut universal hose can cause at this joint.

The hose is built with a durable plastic construction in a white finish, matching the fit, form, and function of the original Mercury Marine equipment it replaces. It is manufactured to Sierra's standard for marine cooling system components, giving boat owners a direct replacement for the factory hose without modification to surrounding fittings or clamps.

This is a port-side specific hose. It is designed only for the thermostat housing to port exhaust manifold connection; the starboard-side connection uses a separate Sierra part number, so confirm which side needs replacement before ordering.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-70943
• Material: Plastic
• Color: White
• Weight: 0.84 pounds
• UPC: 808282227722
• OEM Cross Reference: 32-89749-1
• Application: Thermostat housing to port exhaust manifold
• Engine Fitment: MCM/MIE GM V-8 (454 & 502 cid) engines, 74L, 454 Mag, 502 Mag
• Category: Mercruiser cooling system hose

Fitment

• MCM/MIE GM V-8 (454 & 502 cid) engines
• 74L
• 454 Mag
• 502 Mag

Replaces (OEM)

• Mercury Marine 32-89749-1

Frequently Asked Questions

What does the Sierra 18-70943 hose connect? The Sierra 18-70943 is a molded hose that runs from the thermostat housing to the port exhaust manifold on applicable Mercruiser engines.

Is this hose for the port or starboard side? The 18-70943 is specifically the port-side thermostat housing to exhaust manifold hose; the starboard-side connection requires a different Sierra part number, so verify the side before ordering.

Which engines is the 18-70943 hose designed for? It fits MCM/MIE GM V-8 (454 & 502 cid) engines, including the 74L, 454 Mag, and 502 Mag configurations.

What OEM part number does the Sierra 18-70943 replace? This hose cross-references to Mercury Marine part number 32-89749-1.

What material is the 18-70943 hose made from? It is a molded plastic hose finished in white, matching the original equipment construction for this cooling system connection.

How much does the Sierra 18-70943 hose weigh? The 18-70943 hose weighs 0.84 pounds.

Is the Sierra 18-70943 a genuine OEM part or aftermarket? The 18-70943 is a Sierra-manufactured replacement hose, sold as a direct cross-reference to Mercury Marine 32-89749-1 rather than an OEM Mercury Marine part.

Does the Sierra 18-70943 come with clamps or fittings? The 18-70943 is supplied as the molded hose itself; no clamps or fittings are included based on available product information.

Will the 18-70943 hose fit a Mercruiser 454 Mag or 502 Mag engine? Yes, the 18-70943 is designed to fit Mercruiser 454 Mag and 502 Mag engines along with the MCM/MIE GM V-8 454 and 502 cid platforms.

Why does this hose need to be molded rather than a straight length? The 18-70943 is molded to the specific bend required to route coolant from the thermostat housing to the port exhaust manifold, so it seats without kinking the way a straight-cut hose could at this joint.