Thermostat Cover Gasket – Fits Mercury/MerCruiser 2.5L/3.0L Inline 4-Cylinder (Replaces 27-475901)
Thermostat Cover Gasket – Fits Mercury/MerCruiser 2.5L/3.0L Inline 4-Cylinder (Replaces 27-475901) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat Cover Gasket – Fits Mercury/MerCruiser 2.5L/3.0L Inline ...
Product Details
This high-quality Thermostat Cover Gasket creates a reliable seal between the water thermostat housing cover and the engine block. It is designed for a precise fit on Mercury MerCruiser 2.5L and 3.0L inline 4-cylinder engines (120-140 HP) manufactured from 1982 to the present.
It is an interchangeable part for multiple OEM and aftermarket references, including Mercury/MerCruiser 27-475901, Sierra 18-2831, GLM 31430, and Mallory 9-60012.
- Installs directly between the thermostat housing and the engine block.
- Made from a durable paper/fiber composition to ensure a tight, leak-free seal.
- Specifically designed for use in gasoline marine engine environments.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/MerCruiser | 27-47590 |
| Mercury/MerCruiser | 27-475901 |
| Mercury/MerCruiser | 27-47590B1 |
| Sierra | 18-2831 |
| GLM | 31430 |
| Mallory | 9-60012 |
| Barr | MC47274790 |
| EMP | 27-00307 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser applications, please verify your engine model and serial number range to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 120 GM 153 I/L4 | 120 | 4-Stroke | 1983–1986 | 27-475901 | Applies to serial #s 01206002-01202006 |
| MerCruiser | 140 GM 181 I/L4 | 140 | 4-Stroke | 1982–1986 | 27-475901 | Applies to serial #s 01406002-01402346 |
| MerCruiser | 2.5L GM 153 I/L4 | 120 | 4-Stroke | 1987–1989 | 27-475901 | |
| MerCruiser | 3.0L GM 181 I/L4 | 140 | 4-Stroke | 1987–1989 | 27-475901 | |
| MerCruiser | 3.0L GM 181 I/L4 | 140 | 4-Stroke | 1990–1994 | 27-475901 | |
| MerCruiser | 3.0LX GM 181 I/L4 | 140 | 4-Stroke | 1990–1995 | 27-475901 | |
| MerCruiser | 3.0LX GM 181 I/L4 | 140 | 4-Stroke | 1996–1997 | 27-475901 | |
| MerCruiser | 3.0L GM 181 I/L4 | 140 | 4-Stroke | 1998-present | 27-475901 | Applies to serial #s 0L010042-current |
| MerCruiser | 3.0L TKS Plus | 140 | 4-Stroke | 2014-present | 27-475901 | Applies to serial #s 1G404114 & Up |
| MerCruiser | MC1 (1.32:1) | - | 4-Stroke | 1983 | 27-475901 | Applies to serial # 01326013 |
Technical Specs
- Product Type
- Thermostat Cover Gasket
- Installation
- Between thermostat housing and engine block
- Fuel Type
- Gasoline
- Material
- Paper/Fiber Composition
- Product Dimensions
- 6.0 in (H) x 7.5 in (W) x 1.06 in (L)
- Weight
- 0.01 kg (0.022 lbs)
- Other Technical Attributes
- Used with GM in-line 4 & 6 cylinder engines and Renault 90 engines
What’s in the Box
- 1 x Gasket, Water Distribution (27-475901)
Installation Notes
- Disconnect the battery and allow the engine to cool completely before starting.
- Drain the engine coolant to a level below the thermostat housing.
- Carefully remove the bolts securing the thermostat housing cover.
- Remove the old gasket and thoroughly clean both mating surfaces, ensuring they are free of any old material or residue.
- Position the new gasket correctly on the engine block.
- Reinstall the thermostat housing cover and torque the bolts to the manufacturer's specified value.
- Refill the cooling system with the correct type and amount of coolant.
- Reconnect the battery, start the engine, and carefully inspect for any coolant leaks around the housing as the engine warms up.
Troubleshooting & FAQ
How do I know if this gasket will fit my engine?
This gasket is designed specifically for MerCruiser 2.5L and 3.0L inline 4-cylinder models from 1982 to the present. To ensure a perfect match, please verify your exact engine model, year, and serial number against the compatibility table provided on this page.
What are the signs of a failing thermostat gasket?
Common symptoms of a bad gasket include visible coolant leaks around the thermostat housing, unexplained engine overheating, or discovering that the old gasket material is brittle, cracked, or degraded upon inspection.
Can I reuse my old gasket after servicing the thermostat?
No. Gaskets are critical single-use components designed to compress and create a perfect seal. Reusing an old gasket will likely result in leaks and potential engine damage. Always install a new gasket whenever the housing is opened.
How often should this gasket be replaced?
There is no fixed replacement interval. We recommend replacing the thermostat cover gasket any time the thermostat is serviced, the housing is removed, or if a leak is detected in that area.
Is this an OEM part?
This listing is for a high-quality aftermarket replacement, not an OEM component. It has been engineered to meet or exceed OEM-level specifications using comparable materials and is manufactured in an ISO 9001 certified facility with rigorous batch inspections for quality and consistency.
What are your shipping speed and cost?
We ship worldwide quickly, with typical transit times of 5–15 days for most regions. Standard shipping is free for all orders. Expedited shipping options, where available, will be presented at checkout for an additional fee.
What is your warranty and return policy?
This part is covered by a 1-year warranty that protects against manufacturing defects under normal marine use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. Please see our full policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. If any details differ—even if your model appears in the compatibility list—do not order.
- This product is an aftermarket replacement component, not an original equipment manufacturer (OEM) part.
- Professional installation is strongly recommended for safety, proper function, and to prevent engine damage.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world reliability and performance.
- Fast Global Fulfillment — We offer free standard delivery to most regions with an average transit time of 5–15 days.
- Manufacturer-Direct Value — By working directly with our manufacturing partners, we provide fair pricing without ever compromising on materials or quality control.
Payment & Security
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