Mercury – Thermostat Assembly 75-115 HP 2.1L EFI Four Stroke Outboards – 8M0090819

Keep your 2.1-liter FourStroke running at its sweet spot with the Mercury Thermostat Assembly (8M0090819)—an OEM, 120 °F unit built for 75–115 hp EFI outboards. By opening precisely at 120 °F, it brings the block up to temperature quickly, then meters coolant flow so oil stays thin, combustion stays clean, and warning horns stay silent.

Housed in a rugged, glass-filled composite body, the brass wax element is shielded from corrosion and mineral scale. Mercury includes the molded O-ring and clamping lip right on the housing, so you won’t be hunting seals mid-service. Swap it with basic hand tools, reset your SmartCraft fault code, and head for the next point confident your cooling system is dialed.

Why it earns a spot in your spares box

• Exact 120 °F calibration keeps idle smooth and WOT temps stable in summer chop or spring runoff.

• All-in-one assembly—thermostat, housing, and seal arrive pre-mated for a leak-free fit.

• Corrosion-ready materials withstand salt spray and long layups without sticking shut.

• DIY friendly: four bolts out, old unit lifts free, new one clicks in—back on the trailer in minutes.

Replace that sluggish or sticking thermostat before it sidelines your weekend and keep your Mercury running cool, clean, and efficient all season.