The Buckshot Racing #77 Billet Thermostat Housing Cover Kit is designed as a durable replacement for the original Mercury 90390 A1 thermostat cover used across a broad range of classic Mercury and Mariner V6 two-stroke outboards.
Machined from billet aluminum, these covers replace the aging cast OEM thermostat housings commonly found on 2.0L, 2.4L, and 2.5L Mercury V6 engines. They are intended for engine builders, marine technicians, and owners who want to replace corroded, cracked, warped, or leaking thermostat covers while retaining the factory-style cooling-system layout.
The billet covers are compatible with applications using either factory thermostats or race restrictor washers, making them suitable for stock, performance, and racing cooling-system configurations where the original Mercury 90390A1 cover is used.
Why Replace the Original Thermostat Covers
Many of these Mercury V6 engines have now been in service for decades. The original cast thermostat housings can suffer from corrosion, pitting, cracking, sealing-surface damage or distortion around the mounting bolts.
Once the sealing surface deteriorates, coolant leaks can develop around the thermostat cover and cylinder head. A damaged housing can also make it difficult to achieve even gasket compression.
The Buckshot Racing #77 billet covers provide a stronger, reusable replacement with a precision-machined sealing surface designed to restore proper thermostat housing fit.
Fits Mercury 2.0L, 2.4L & 2.5L V6 Two-Strokes
The Mercury 90390A1 thermostat cover was used across a wide range of Mercury V6 two-stroke engines.
Compatible applications include selected V-135, V-150, V-175 and V-200 engines, along with XR2, XR4 / Magnum II, XR6 / Magnum III, XRi, 220 Laser, Magnum, Marathon, Work and Offshore models.
The same thermostat-cover design is also found on selected 150 HP, 175 HP and 200 HP 2.5L V6 engines, as well as 150/200 Pro Max / Super Magnum, 225 Pro Max, 225X Pro Max, 2.5L Offshore, SST-120, S2000 and S3000 applications.
Mercury also used the 90390A1-style thermostat cover in selected SportJet and Jet Drive powerheads, including 175XR2, 210 Carb, and 240 EFI configurations.
Because Mercury used different cylinder heads and cooling systems across its long V6 production run, the most reliable fitment check is to confirm that the engine originally uses Mercury thermostat cover 90390A1.
Retains Factory Thermostats or Restrictor Washers
The billet covers retain the original cooling-system concept. For production and recreational engines, the covers can be used with the correct Mercury-style thermostat and seal for the specific engine.
Many conventional V6 applications use the familiar approximately 143–147°F thermostat family, while some later or performance applications use 120°F thermostats.
For compatible race or modified cooling systems, the same billet housing can also retain restrictor washers in place of thermostats.
Thermostat temperature or restrictor size should always match the cooling-system configuration of the exact engine rather than being selected only by horsepower.
Kit Contents
Each Buckshot Racing #77 kit includes two (2) billet thermostat cover outlets, enough for one Mercury V6 engine, along with four (4) socket-head mounting bolts. The supplied hardware replaces the original thermostat-cover screws used in many applications, including Mercury 10-35386 and 10-37562.
Optional cooling-system packages are also available, depending on the engine and intended use.
Two (2) 143 Thermostats and Seals Kit
Two (2) 120 Thermostats and Seals Kit
Two (2) Race Restrictor Washers and Seals Kit
Billet Thermo Cover Kit Only
Cooling-System Service Tip
When replacing thermostat covers, inspect the complete thermostat area before assembly.
Remove corrosion and old gasket material from the cylinder-head sealing surface and check for pitting around the water passages. Inspect the thermostats, seals, restrictor washers and water hoses while the covers are removed.
A new billet cover will not correct a damaged cylinder-head sealing surface, blocked cooling passage or incorrect thermostat configuration, so these items should be checked during installation.
The mounting bolts should be tightened evenly to the proper specification for the application. Excessive torque is unnecessary and can damage threads or distort surrounding components.
Buckshot Racing #77 Builder Tech Tip
Cooling-system modifications should be treated as part of the complete engine combination.
A stock fishing engine, high-performance lake motor, and dedicated race engine may require very different thermostat or restrictor arrangements.
Water pressure, engine height, gearcase water pickup, operating RPM, and cylinder-head configuration all affect cooling-system requirements.
The Buckshot Racing #77 Billet Thermostat Housing Cover Kit provides a durable replacement for Mercury 90390A1 while allowing builders to retain the factory thermostat system or configure compatible restrictor washers for performance use.
Contact Mike Hill at +1-714-697-1716 for tech support.