Sierra 18-1977-1 Thermostat Housing for Mercruiser 305 cid V-8 (1977-1982), Replaces 4765100, 6218461

The Sierra 18-1977-1 is a marine thermostat housing built to replace the factory housing on Mercruiser 305 cid V-8 sterndrive engines produced in 1977-1982. It is sand cast and machined to exact specifications, then primed and painted to withstand the harsh marine environment, and is finished in white with a polished surface. The housing mounts to the engine block and holds the thermostat in place while sealing the cooling passages, so a worn, cracked, or corroded original housing is a common reason for coolant leaks, overheating, or an improperly seating thermostat. Installing the 18-1977-1 restores a proper seal at this connection point and returns the cooling system to factory-correct operation.

This housing is a direct cross-reference for GM/Mercruiser OEM housing numbers 4765100 and 6218461, so it fits in place of those original parts on the applicable 305 cid V-8 engines without modification. It ships as a single housing unit and is intended as a like-for-like replacement, not an upgrade kit, so existing thermostats, gaskets, and hardware from the original installation can be reused if they are still in serviceable condition.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-1977-1
• Product Type: Thermostat Housing
• Engine Fitment: Mercruiser 305 cid V-8
• Model Years: 1977-1982
• OEM Cross-Reference: 4765100, 6218461
• Weight: 1.51 pounds
• Package Dimensions: 17.6 H x 8.7 L x 12.3 W (centimetres)
• Material: Metal, sand cast and machined
• Finish: Polished
• Color: White
• Country of Origin: China
• UPC: 808282198206

Fitment

• Mercruiser 305 cid V-8 engines, 1977-1982

Replaces (OEM)

• 4765100
• 6218461

Frequently Asked Questions

What engines does the Sierra 18-1977-1 thermostat housing fit? The Sierra 18-1977-1 fits Mercruiser 305 cid V-8 engines built in 1977-1982.

Does the 18-1977-1 replace OEM part number 4765100? Yes, the Sierra 18-1977-1 is a direct cross-reference for OEM housing number 4765100 on the applicable 305 cid V-8 Mercruiser engines.

Does the 18-1977-1 also replace OEM part number 6218461? Yes, 6218461 is the other OEM number the Sierra 18-1977-1 housing replaces on 1977-1982 305 cid V-8 engines.

What is the 18-1977-1 housing made of? It is a metal housing that is sand cast and machined to exact specifications, then primed and painted, with a polished white finish for long life in a marine environment.

How much does the Sierra 18-1977-1 thermostat housing weigh? It weighs 1.51 pounds.

What are the package dimensions of the 18-1977-1? The packaged housing measures 17.6 H x 8.7 L x 12.3 W in centimetres.

Does the 18-1977-1 include the thermostat and gasket? The 18-1977-1 is the thermostat housing itself; it ships as a single housing unit.

Is the Sierra 18-1977-1 a genuine Sierra part or aftermarket generic? The 18-1977-1 is manufactured by Sierra, a marine parts brand, and is sold under Sierra's own part number as its housing for this application.

Why would I need to replace my thermostat housing? A cracked, corroded, or leaking original housing on a 305 cid V-8 Mercruiser engine is a common cause of coolant leaks and overheating, and the Sierra 18-1977-1 is built to restore a proper seal in place of the worn factory unit.

Where is the Sierra 18-1977-1 manufactured? The country of origin for the 18-1977-1 housing is China.

What color and finish does the 18-1977-1 come in? The 18-1977-1 housing has a white color with a polished finish.

Can I reuse my old thermostat and hardware with the 18-1977-1? Since the 18-1977-1 is a like-for-like replacement housing, an existing thermostat, gasket, and hardware can be reused as long as they are still in serviceable condition.