Thermostat for Mercury / Mariner Outboard
Fits DFI Optimax 2-Stroke Models – 200HP, 225HP, 250HP, 300HP

This high-quality aftermarket thermostat is designed to maintain proper engine temperature and cooling performance in Mercury Optimax engines.

Will fit the following Mercury/Mariner DFI Optimax models:
• 200 HP DFI – USA models from serial 0G590000 and up
• 225 HP DFI – USA models from serial 0G590000 and up
• 250 HP DFI – USA models from serial 1B426561 and up
• 300 HP DFI – USA models from serial 1E001867 and up

Replaces OEM Part Number:
• Mercury / Mariner 8M0057307
(OEM part number used for reference only. This is a marine-grade aftermarket replacement.)

Why Buy from SSI Marine?
• Marine-grade aftermarket part
• UK-based stock for fast shipping
• Same-day dispatch on orders before 1 PM (Mon–Fri)
• Collection available from our Leigh, Manchester unit
• Trusted supplier with years of marine experience
• VAT invoice available upon request
• Expert help available — message us if you’re unsure about fitment

⚠️ Please confirm compatibility with your engine model and serial number before purchasing. If in doubt, contact us and our team will be happy to help.

Thermostat for Mercury Mariner 200 225 250 300 HP DFI Optimax Outboard | Replaces 8M0057307