Mercury Outboard Thermostat Assembly 120°F – 8M0090819
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You have 30 days to request a return. All sale items are final sale.
The Mercury / Quicksilver 8M0090819 Thermostat Assembly is a genuine OEM 120°F thermostat with integrated housing, designed for Mercury EFI 4-stroke outboards.
Unlike a standard thermostat, this is a complete assembly that includes both the thermostat and its housing, ensuring proper sealing, alignment, and coolant flow. It regulates engine temperature by controlling water flow through the powerhead, allowing the engine to warm up quickly and maintain stable operating temperature under load.
The 120°F calibration is critical for these engines, supporting proper fuel mapping, combustion efficiency, and corrosion control in raw water cooling systems. Built to Mercury Marine specifications, it provides consistent thermal response, long service life, and exact fitment.
Key Features
- Genuine Mercury / Quicksilver OEM assembly
- 120°F (49°C) temperature rating
- Complete unit: thermostat + housing
- Designed for raw water cooled outboards
- Maintains proper engine operating temperature
- Ensures correct coolant flow and sealing
- Direct OEM replacement (no modification required)
Engine Compatibility
Mercury 4-Stroke EFI Outboards (2.1L Platform)
Fits:
- 75 HP
- 80 HP
- 90 HP
- 100 HP
- 115 HP
➡️ Also used on:
- EFI SeaPro models
- EFI Jet drive variants
➡️ Designed for:
- 2.1L 4-cylinder EFI FourStroke engines
Important Fitment Notes
- ✔ Raw water cooled systems only
- ✔ Must match 120°F spec for proper operation
- ❌ Not compatible with Verado engines
- ✔ Includes housing – not interchangeable with thermostat-only designs
Specifications
- Part Number: 8M0090819
- Temperature Rating: 120°F (49°C)
- Type: Thermostat assembly (with housing)
- Cooling System: Raw water cooled
- Engine Platform: Mercury 2.1L EFI 4-stroke
- Construction: Marine-grade composite/metal housing
What’s Included
- Thermostat
- Thermostat housing assembly
When This Part Needs Replacement
- Engine overheating or running hot
- Engine running too cold (stuck open)
- Coolant leaks at thermostat housing
- Corrosion or damage to housing
- Routine maintenance on high-hour engines
Installation Notes
- Replace as a complete assembly (do not reuse old housing)
- Inspect sealing surfaces and hoses
- Torque evenly to avoid housing distortion
- Verify proper operating temperature after install
Alternate / Superseded Part Numbers
OEM Cross References
- Mercury / Quicksilver: 8M0090819
- Superseded by: 8M0204728
Shipping
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
💡 Parts Desk Insight
If you’re seeing leaks around the thermostat area, replace the whole assembly—not just the thermostat. These housings warp and corrode over time 👍
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.