A.A Thermostat & Gasket Kit for MerCruiser 2.5L / 3.0L (120, 140) – Direct OEM Fit, Corrosion-Resistant

This A.A replacement kit contains the thermostat and gasket engineered to fit a range of MerCruiser 4- and 6-cylinder engines used across multiple model years. It replaces common part numbers and is sized for direct installation, helping restore correct coolant flow and seal integrity without the need for extensive modifications. The kit is compact, corrosion-resistant, and supplied with components meant to simplify routine marine engine maintenance.

Which MerCruiser engines and model years will this kit fit?

The kit is specified for MerCruiser 120 (2.5L) and 140 (3.0L) four-cylinder engines and several six-cylinder 165 applications across multiple years. Fitment spans model years from the late 1960s through the late 1990s for the listed engine codes. Always confirm against your engine’s part number range before purchase.

• Compatible with 120 - 2.5L / L4 and 140 - 3.0L / L4 engine families
• Works for various production years: 1968–1989, 1990–1997, 1998–2000 depending on engine code
• Replaces OEM numbers including 59078T3, 18-3650, 47590 and related cross-references

What does the kit include and how straightforward is installation?

The package contains one thermostat and one gasket sized to match the original components. Installation is a standard cooling-system service task: drain coolant, remove housing, swap parts, and torque to factory specs. No special machining or adapters are required when matched to the correct engine application.

• Includes: 1x thermostat (59078 / 18-3550) and 1x gasket (27-47590-1 / 18-2831)
• Designed for direct replacement of listed OEM part numbers
• Fits into the stock thermostat housing without modification

How will this replacement affect engine cooling and maintenance?

Replacing a worn thermostat and a deteriorated gasket restores proper coolant control and a reliable seal at the housing. That helps the engine reach and maintain its designed operating temperature and reduces the chance of external leaks. Use with fresh coolant and follow torque specs to ensure long-term performance.

• Restores correct thermostat opening temperature and coolant flow pattern
• Replaces aged gaskets that often cause housing leaks
• Supports routine cooling-system refresh during seasonal maintenance

Are these parts genuine OEM or aftermarket replacements?

This A.A kit is an engineered aftermarket replacement that cross-references the listed OEM numbers. It’s produced to meet fit and function expectations for the specified MerCruiser models. Buyers seeking original Mercury/Marine branded packaging should compare part numbers and vendor sourcing before purchase.

• Cross-references multiple OEM numbers such as 59078T3 and 18-3650
• Manufactured to match critical dimensions and sealing surfaces
• Intended for mechanics and DIYers familiar with marine engine servicing

Who is this for? Boat owners, marine mechanics, and restoration specialists working on MerCruiser 2.5L and 3.0L engines who need a reliable thermostat and gasket replacement. If you maintain classic or later-model MerCruiser outboards and sterndrives listed in the fitment, this kit offers a convenient, cross-referenced solution to restore proper cooling system function during routine overhaul or troubleshooting.