# 27887978 Mercury MerCruiser Gasket | Genuine Quicksilver OEM Part

## 🔧 Product Description

**Genuine Quicksilver Thermostat Gasket / Seal - Part Number: 27-887978**

Genuine Quicksilver thermostat gasket / seal used on Mercury and Mariner outboard thermostat assemblies. This gasket is part of the 27-62386 / 27-62386001 / 27-887978 family and is used across a wide range of Mercury / Mariner outboards where the thermostat housing diagram specifies this rubber thermostat seal.

## ⚙️ Key Features

-   Genuine Quicksilver OEM thermostat gasket
-   Correct Mercury part number 27-887978
-   Listing reference: 27887978
-   Rubber thermostat seal / gasket
-   Supersedes earlier 27-62386 / 27-62386001 family references where specified
-   Used on Mercury / Mariner outboards across broad HP ranges

## 🚤 Compatibility

### Commonly used on

-   Mercury / Mariner outboard thermostat assemblies
-   Thermostat housing reseal service
-   Outboard cooling-system maintenance where rubber thermostat seal 27-887978 is specified

### Typically suits

-   Engine models:
-   Mercury / Mariner 8HP through 400HP outboard thermostat seal applications where 27-887978 is specified
-   Mercury 10HP to 300HP outboards using the 27-62386 / 27-887978 thermostat seal family
-   Mercury 75HP, 90HP, 115HP and 125HP outboard thermostat assemblies where specified
-   Mercury V6 135HP, 150HP, 175HP, 200HP, 225HP and 250HP thermostat housings where specified
-   Mercury OptiMax / DFI thermostat applications using seal 27-887978
-   Mercury Verado and FourStroke thermostat service applications where 27-887978 is listed
-   Mariner matching outboard thermostat assemblies using the same seal family
-   HP Range: commonly 8HP - 400HP where specified
-   Engine Type: Mercury / Mariner outboard cooling systems
-   System Type: Thermostat gasket / rubber thermostat seal

## 🔌 Function

The gasket seals the thermostat in the housing so cooling water flows through the intended passages and does not leak around the thermostat cover.

## ⚠️ Common Signs of Failure

-   Cooling water leak at thermostat cover
-   Thermostat removed and seal disturbed
-   Rubber seal brittle, flattened or swollen
-   Salt or corrosion around thermostat housing
-   Overheating after poor thermostat seal
-   Scheduled thermostat service due

## 🔄 Supersession & Cross Reference

### OEM Supersession Chain

-   27-887978 current OEM thermostat gasket reference
-   27-62386001 earlier OEM thermostat seal reference
-   27-62386 earlier OEM thermostat seal reference
-   62386B related earlier thermostat seal reference

### OEM / Related Numbers

-   27-887978
-   887978
-   27887978
-   27-62386001
-   62386001
-   27-62386
-   62386
-   62386B
-   Thermostat gasket
-   Thermostat seal
-   Rubber thermostat gasket

### Aftermarket / Verified Equivalents

-   Sierra: 18-0182
-   Mallory: 9-60002
-   GLM / aftermarket reference: 30610
-   Aftermarket reference: 424
-   Aftermarket reference: 540-32
-   Recmar: REC27-62386001
-   Aftermarket thermostat seal equivalents for 27-887978 / 27-62386 applications

## 📦 Condition

-   Genuine Quicksilver part
-   Brand new
-   Supplied in original or equivalent packaging

## Details

- **Price:** 5.9 AUD
- **Vendor:** Quicksilver
- **Type:** Gaskets & Seals
- **Tags:** Quicksilver Marine Parts | Oils, Service Kits & Engine Components

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 5.90 AUD | In stock |

## Images

- 27887978 Mercury MerCruiser Gasket | Genuine Quicksilver OEM Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/27887978-mercury-mercruiser-gasket-genuine-quicksilver-oem-part)
> Updated: 2026-09-18