8M0139434 Mercury MerCruiser Thermostat | Genuine Quicksilver OEM Part
8M0139434 Mercury MerCruiser Thermostat | Genuine Quicksilver OEM Part
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🔧 Product Description
Genuine Quicksilver 125°F EFI Four-Stroke Thermostat - Part Number: 8M0139434
A genuine Quicksilver 125°F thermostat for selected Mercury and Mariner 15HP and 20HP EFI four-stroke outboards.
The thermostat regulates cooling-water flow through the cylinder block, allowing the engine to reach its correct operating temperature before opening to control heat under load.
⚙️ Key Features
- Genuine Quicksilver OEM thermostat
- Correct Mercury part number 8M0139434
- 125°F calibrated operating temperature
- Used on later 15HP and 20HP EFI four-stroke outboards
- Recmar and Tohatsu equivalents available
🚤 Compatibility
Commonly used on
- Mercury and Mariner EFI four-stroke cylinder-block cooling systems
- Corresponding Tohatsu-manufactured EFI engine families
Typically suits
- Engine models:
- Mercury 15HP EFI four-stroke - serial 0R833820 and above
- Mercury 20HP EFI four-stroke - serial 0R833820 and above
- Mariner 15HP EFI four-stroke corresponding production
- Mariner 20HP EFI four-stroke corresponding production
- Tohatsu 9.9HP, 15HP and 20HP EFI applications using thermostat 3RS-01030-0
- HP Range: 9.9HP - 20HP
- Engine Type: Mercury / Mariner / Tohatsu EFI four-stroke outboard
- Year Range: Approximately 2017 onward
🔌 Function
The thermostat controls cooling-water flow so the engine warms correctly and then maintains a stable operating temperature.
⚠️ Common Signs of Failure
- Engine overheats because the thermostat remains closed
- Engine runs excessively cold
- Rough running during warm-up
- Salt or corrosion prevents thermostat movement
- Engine temperature changes erratically
🔄 Supersession & Cross Reference
OEM Supersession Chain
- 8M0139434 current OEM thermostat reference
OEM / Related Numbers
- 8M0139434
- Tohatsu: 3RS-01030-0
- Thermostat gasket supplied with selected aftermarket kits
- UPC: 745061050396
Aftermarket / Verified Equivalents
- Recmar: REC8M0139434
- Tohatsu: 3RS-01030-0
- GHmarine: 18-43175 thermostat service kit
📦 Condition
- Genuine Quicksilver part
- Brand new
- Supplied in original or equivalent packaging
Shipping & Delivery
Shipping & Delivery
Flat-rate shipping Australia-wide — $14.99 per order, no matter how many parts you add. Orders dispatch from our Kadina, South Australia store. Need it urgently or want to collect in person? Call us on 0412 532 984 before ordering.
Returns & Warranty
Returns & Warranty
14-day change-of-mind returns — if it's not right or you ordered the wrong part, send it back within 14 days in new, unused condition for a refund or exchange. Manufacturer warranties apply to new parts. Full details in our Refunds & Returns policy.
Not sure this fits?
Not sure this fits?
Ask us before you buy — we check part numbers and fitment every day. Call 0412 532 984 (Mon–Fri 8.30am–4.30pm) or message us through the contact page with your engine or vehicle details.
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