# 804540 Mercury MerCruiser Thermostat | Genuine Quicksilver OEM Part

🔧 Product Description

  

Genuine Quicksilver Thermostat - Part Number: 804540

  

Genuine Quicksilver/Mercury thermostat for selected Mercury and Mariner small outboard cooling systems. This OEM thermostat is used across specific small carburetted and international two-cylinder outboard applications and has been superseded through later Mercury thermostat service references.

  

⚙️ Key Features

  

• Genuine Quicksilver/Mercury OEM thermostat

• Used on selected Mercury / Mariner small outboard cooling systems

• Supersedes through later 8M0228411 / 8M0228413 service references

• Helps regulate engine operating temperature

• Direct replacement for 804540 / 853704 / 803665 thermostat family applications

  

🔄 Supersession & Cross Reference

  

OEM Supersession Chain:

  

• 8M0228413 → Supersedes 8M0228411

• 8M0228411 → Supersedes 804540

• 804540 → Supersedes 853704

• 853704 → Supersedes 803665

• 803665 earlier OEM reference

  

OEM / Related Numbers:

  

• 804540

• 853704

• 803665

• 8M0228411

• 8M0228413

• Tohatsu: 350-01030-2

• Tohatsu: 350-01030-1

• Tohatsu: 350-01030-0

  

Aftermarket / Verified Equivalents:

  

• REC: REC804540

• Aftermarket thermostat equivalents available under Tohatsu 350-01030 family where matched by application

  

🚤 Compatibility

  

Commonly used on:

  

• Mercury / Mariner small outboard cylinder block thermostat applications

• Mercury / Tohatsu-built small outboard cooling systems

  

Typically suits:

  

• Engine models:

• Mercury small carburetted 2HP-6HP models where 804540 thermostat family is specified

• Mercury 4HP Carb 4-Stroke, serial range 0R067090 - 0R411837

• Mercury 25HP 2-Cylinder International, serial range 0N018456 - 0N055504

• Mercury 30HP 2-Cylinder International, serial range 0N001875 - 0N055504

• Mercury / Mariner small outboard applications where the cylinder block parts diagram specifies 804540, 853704, 803665, 8M0228411 or 8M0228413

  

• HP Range: 2HP - 30HP where specified by parts diagram

• Engine Type: Mercury / Mariner small outboard cooling-system thermostat

• Year Range: Application dependent by 0N / 0R serial range and model family

  

🔌 Function

  

The thermostat controls cooling-water circulation so the engine can warm up correctly and maintain a stable operating temperature. A correct thermostat helps prevent overcooling, overheating, poor running and temperature fluctuation.

  

Common signs of failure:

  

• Engine overheating warning

• Engine running too cold

• Slow warm-up

• Thermostat stuck open or closed

• Salt or scale deposits around thermostat

• Poor idle or inconsistent running temperature

• Reduced cooling-system performance

  

📦 Condition

  

• Genuine Quicksilver part

• Brand new

• Supplied in original or equivalent packaging

## Details

- **Price:** 82.8 AUD
- **Vendor:** Quicksilver
- **Tags:** Quicksilver Marine Parts | Oils Service Kits & Engine Components

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 82.80 AUD | In stock |

## Images

- 804540 Mercury MerCruiser Thermostat | Genuine Quicksilver OEM Part

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> Source: [Sawley's Auto and Marine](www.sawleysautoandmarine.com.au/products/804540-mercury-mercruiser-thermostat-genuine-quicksilver-oem-part)
> Updated: 2026-05-17