Weekend coming up? Order this Mercury **THERMAL SWITCH, (Normally Open 130-110 degrees)** now for fast shipping. Most orders placed by 1pm ship today so you’re fishing, not fixing.

Factory-built to exact Mercury Marine specifications, this component ensures reliable operation across all engine RPM ranges. Part number 866089 is manufactured to exact Mercury Marine factory specifications for precision installation and optimal performance. Constructed from premium marine-grade materials designed to withstand harsh saltwater and freshwater environments.

Genuine Mercury Marine part 866089 isn’t just a replacement – it’s an investment in your engine’s longevity. Factory engineering ensures optimal performance while cheap alternatives lead to repeated repairs.

FITS: 4-5HP MERCRUISER

• Fits MERCRUISER 4-5HP engines
• Compatible HP: 4HP, 5HP
• Covers 19 serial number ranges
• Configurations: Outboard
• OEM genuine Mercury Marine part

COMPLETE SERIAL NUMBER COMPATIBILITY:

4HP Models

• 4HP OUTBOARD (Mercruiser): 0M615000-0W300012, 0W300013-0W309999, 0W310000-0W649999, 0W650000-1A063239

5HP Models

• 5HP OUTBOARD (Mercruiser): 0M600000-0W300009, 0W300010-0W309999, 0W310000-0W649999, 0M600000-0W300754, 0W300755-0W309999, 0W310000-0W649999, 0M317000-0W090899, 0W090900-0W689999, 0M317000-0W090899, 0W090900-0W689999

Looking for your engine serial number? Our helpful guide shows you exactly where Mercury places serial numbers on different models.

Want to verify compatibility for part 866089? Use our parts finder tool for instant confirmation. Still have questions? No problem – use the contact buttons at the bottom of this page to reach us by text, call, or email.

Trusted by boaters since 1985. Discount pricing on OEM Mercury parts with cheap shipping options.