# 8M0008243 Mercury MerCruiser Thermostat Cover | Genuine Quicksilver OEM Part

🔧 Product Description

  

Genuine Quicksilver Thermostat Cover - Part Number: 8M0008243

  

A genuine Quicksilver thermostat cover used on selected Mercury and Mariner small and mid-range FourStroke outboard cooling systems. This cover seals the thermostat cavity and retains the thermostat and gasket in the correct position.

  

⚙️ Key Features

  

• Genuine Quicksilver OEM thermostat cover

• Correct Mercury part number 8M0008243

• Superseded to later 8M0188835 service reference

• Replaces / cross-references with 857080 and 8250311 cover references

• Also cross-references with Yamaha 6H3 thermostat cover family

  

🔄 Supersession & Cross Reference

  

OEM Supersession Chain:

  

• 8M0188835 → Supersedes 8M0008243

• 8M0008243 earlier OEM thermostat cover reference

• 857080 related earlier Mercury / Mariner thermostat cover reference

• 8250311 related thermostat cover reference

  

OEM / Related Numbers:

  

• 8M0008243

• 8M0188835

• 857080

• 8250311

• 825031C

• 10-88348935 related M6 x 35 screw

• 8M0241960 related later screw reference

  

Yamaha Cross-Referenced Numbers:

  

• Yamaha: 6H3-12413-00-00

• Yamaha: 6H3-12413-00-1S

• Yamaha: 6H3-12413-00-94

• Yamaha: 6H3-12413-00-9M

• Yamaha: 6H3-12413

  

Aftermarket / Verified Equivalents:

  

• Outboard Spares: OSTC6H3 equivalent

  

🚤 Compatibility

  

Commonly used on:

  

• Mercury / Mariner FourStroke thermostat cover applications

• Yamaha-sourced small and mid-range FourStroke thermostat cover applications where specified

  

Typically suits:

  

• Engine models:

• Mercury 8HP FourStroke - serial 0P086824 to 0P400999

• Mercury 9.9HP FourStroke - serial 0G760300 to 1B226999

• Mercury 9.9HP FourStroke - serial 0P075166 to 0P400999

• Mercury 13.5HP FourStroke - serial 0P134638 to 0P400999

• Mercury 13.5HP FourStroke - serial 0P401000 and up

• Mercury 15HP FourStroke - serial 0G760300 to 1B226999

• Mercury 15HP FourStroke - serial 0P075166 to 0P400999

• Mercury 15HP FourStroke - serial 0P401000 and up

• Mercury 15HP FourStroke - serial 1B227000 to 1B727495

• Mercury 25HP FourStroke - serial 0P153500 to 0P388282

• Mercury 25HP FourStroke - serial 0T409000 to 1B344298

• Mercury 30HP FourStroke - serial 0P153500 to 0P400999

• Mercury 30HP FourStroke - serial 0T409000 to 1B226999

• Mercury 30HP FourStroke - serial 1C456300 and up

• Mercury 30HP EFI 3-cylinder FourStroke - serial 0P153500 to 0P400999

• Mercury 30HP EFI 3-cylinder FourStroke - serial 0T409000 to 1B226999

• Mercury 30HP EFI 3-cylinder FourStroke - serial 1C109093 to 1C456299

• Mercury 30HP EFI 3-cylinder FourStroke - serial 1C456300 and up

• Mercury 35HP EFI Jet 4-cylinder FourStroke - serial 1C453840 and up

• Mercury 40HP FourStroke - serial 0P153500 to 0P400999

• Mercury 40HP FourStroke - serial 0P401000 and up

• Mercury 40HP FourStroke - serial 0T409000 to 1B226999

• Mercury 40HP FourStroke - serial 1B227000 to 1B344306

• Mercury 40HP FourStroke - serial 1C000001 to 1C018825

• Mercury 40HP FourStroke - serial 1C018826 and up

• Mercury 40HP EFI 3-cylinder FourStroke - serial 0P153500 to 0P400999

• Mercury 40HP EFI 3-cylinder FourStroke - serial 0P401000 to 0P515896

• Mercury 40HP EFI 3-cylinder FourStroke - serial 0T409000 to 1B226999

• Mercury 40HP EFI 3-cylinder FourStroke - serial 1B227000 to 1B355027

• Mercury 40HP EFI 3-cylinder FourStroke - serial 1C000001 to 1C043416

• Mercury 40HP EFI 3-cylinder FourStroke - serial 1C043417 to 1C456299

• Mercury 40HP EFI 3-cylinder FourStroke - serial 1C456300 and up

• Mercury 40HP EFI 4-cylinder FourStroke - serial 0P153500 to 0P400999

• Mercury 40HP EFI 4-cylinder FourStroke - serial 0P401000 to 0P515896

• Mercury 40HP EFI 4-cylinder FourStroke - serial 0T409000 to 1B355222

• Mercury 40HP EFI 4-cylinder FourStroke - serial 1C000001 to 1C050251

• Mercury 40HP EFI 4-cylinder FourStroke - serial 1C050252 to 1C453839

• Mercury 40HP EFI 4-cylinder FourStroke - serial 1C453840 and up

• Mercury 40HP EFI Jet 4-cylinder FourStroke - serial 1C051324 to 1C453839

• Mercury 40HP EFI Jet 4-cylinder FourStroke - serial 1C453840 and up

• Mercury 40HP EFI SeaPro 4-cylinder FourStroke - serial 1C453840 and up

• Mercury 50HP EFI 4-cylinder FourStroke - serial 1C453840 and up

• Mercury 60HP EFI 4-cylinder FourStroke - serial 1C453840 and up

• Mercury 60HP EFI SeaPro FourStroke - serial 1C453840 and up

• Mercury Formula 60 - serial 1C104574 and up

• Mercury 60R EFI Racing FourStroke - serial 1C615064 and up

• Yamaha F9.9 / F15 / F20 / F25 / F30 / F40 / F45 / F50 / F60 / F70 applications where Yamaha 6H3-12413 thermostat cover family is specified

• Yamaha 50G / 60F / 70B 2-stroke applications where Yamaha 6H3 thermostat cover family is specified

  

• HP Range: Mercury / Mariner 8HP - 60HP FourStroke where specified, plus Yamaha 9.9HP - 70HP applications where specified

• Engine Type: Mercury / Mariner FourStroke outboard and selected Yamaha outboard applications

• System Type: Thermostat housing cover / cooling system cover

  

🔌 Function

  

The thermostat cover seals the thermostat cavity and helps maintain correct cooling system flow through the thermostat housing.

  

Common signs of failure:

  

• Water leak around thermostat cover

• Cracked or corroded cover

• Thermostat gasket will not seal correctly

• Overheating or cooling-system pressure loss

• Damaged cover during thermostat service

  

📦 Condition

  

• Genuine Quicksilver part

• Brand new

• Supplied in original or equivalent packaging

## Details

- **Price:** 14.35 AUD
- **Vendor:** Quicksilver
- **Tags:** Quicksilver Marine Parts | Oils Service Kits & Engine Components

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 14.35 AUD | In stock |

## Images

- 8M0008243 Mercury MerCruiser Thermostat Cover | Genuine Quicksilver OEM Part

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> Source: [Sawley's Auto and Marine](www.sawleysautoandmarine.com.au/products/8m0008243-mercury-mercruiser-mercury-thermostat-cover-genuine-quicksilver-oem-part)
> Updated: 2026-05-17