Cylinder Head Gasket – Fits Tohatsu/Mercury 40-50 HP (Replaces 3C8-01005-4)
Cylinder Head Gasket – Fits Tohatsu/Mercury 40-50 HP (Replaces 3C8-01005-4) 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).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Cylinder Head Gasket – Fits Tohatsu/Mercury 40-50 HP (Replaces 3C8-...
Product Details
This high-quality Cylinder Head Gasket ensures a perfect seal between the cylinder head and engine block for select Tohatsu and Mercury 40-50 HP 2-stroke outboard models. It is designed for 2003 Tohatsu M40D2, M50D2, NS40D2, and NS50D2 engines, as well as various Mercury 40-50 HP models including the 40 International and 40 MXL SEAPRO series.
It serves as a direct cross-reference for Tohatsu part numbers 3C8-01005-4 and 3C8-01005-5, Mercury 27-8M0062091 and 27-81293910, and Sierra 18-3850.
- Installs as a direct replacement for the original part.
- Made from premium sealing materials to withstand high combustion temperatures.
- Engineered to maintain a proper seal and prevent coolant or combustion gas leaks.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By |
|---|---|---|
| Tohatsu | 3C8-01005-4 | 3C8-01005-5 |
| Mercury | 27-8M0062091 | |
| Mercury | 27-81293910 | |
| Sierra | 18-3850 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Fits specific 2003 Tohatsu 40-50 HP 2-stroke models.
Compatible with various 40-50 HP Mercury 2-stroke outboards, including International, MXL SEAPRO, Lightning, Marathon, and 50MH series.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Tohatsu | M40D2 | 40 | 2-Stroke | 2003 | 3C8-01005-4 | Superseded by 3C8-01005-5 |
| Tohatsu | M50D2 | 50 | 2-Stroke | 2003 | 3C8-01005-4 | Superseded by 3C8-01005-5 |
| Tohatsu | NS40D2 | 40 | 2-Stroke | 2003 | 3C8-01005-4 | Superseded by 3C8-01005-5 |
| Tohatsu | NS50D2 | 50 | 2-Stroke | 2003 | 3C8-01005-4 | Superseded by 3C8-01005-5 |
| Mercury | 40 (International) | 40 | 2-Stroke | 27-8M0062091 | Also fits 27-81293910 | |
| Mercury | 40 (MXL SEAPRO) | 40 | 2-Stroke | 27-8M0062091 | Also fits 27-81293910 | |
| Mercury | Lightning | 40 | 2-Stroke | 81293910 | Serial No. 0N000001-0N056164 | |
| Mercury | Lightning XR | 40 | 2-Stroke | 81293910 | Serial No. 0N056165 & Up | |
| Mercury | Marathon | 40 | 2-Stroke | 81293910 | Serial No. 0N037781-0N056164 | |
| Mercury | MXL | 40 | 2-Stroke | 81293910 | Serial No. 0N037781-0N056164 | |
| Mercury | 50MH | 50 | 2-Stroke | 81293910 | Serial No. 0N051023-0N056164 & 0N056165 & Up |
Technical Specs
- Product Type
- Cylinder Head Gasket
- Installation
- Direct replacement
- Fuel Type
- Gasoline
- Housing Material
- Premium sealing material
- Dimensions
- 35.0 cm L x 15.0 cm W x 2.0 cm H
- Operating Temperature
- Designed to withstand high combustion temperatures
- Warranty
- Typically 1-year limited warranty (varies by manufacturer)
- Other Technical Attributes
- Designed to maintain a proper seal between cylinder head and engine block
What’s in the Box
- 1 x Cylinder Head Gasket (Replaces 3C8-01005-4 / 3C8-01005-5)
Installation Notes
- Ensure the engine is cool and the battery is disconnected.
- Drain the engine coolant completely.
- Carefully remove the cylinder head cover and the old gasket.
- Thoroughly clean both the engine block and cylinder head mating surfaces. Remove all old gasket material, oil, and debris.
- Position the new gasket, ensuring correct alignment with all bolt holes and passages.
- Reinstall the cylinder head. Tighten the bolts to the manufacturer-specified torque in the correct sequence as detailed in your service manual.
- Refill the cooling system, restart the engine, and carefully check for any leaks.
Troubleshooting & FAQ
How do I know if this gasket fits my engine?
First, check the Part Number Matrix on this page to see if it cross-references your current part number. Next, review the Engine & Model Compatibility table to confirm your specific model and year are listed. For best results, visually compare the gasket to your old part before ordering.
What are the signs of a failing cylinder head gasket?
Common symptoms include engine overheating, a noticeable loss of power, white smoke from the exhaust (burning coolant), milky or foamy oil, or bubbles in the radiator or coolant reservoir. These indicate a breach in the seal between the cylinder head and engine block.
Is any sealant required for installation?
Most modern head gaskets are designed to be installed dry without any additional sealants. Applying sealant can interfere with the gasket's ability to create a proper seal. Always consult your engine's specific service manual for the manufacturer's official recommendation.
What is the difference between Tohatsu part 3C8-01005-4 and 3C8-01005-5?
The part number 3C8-01005-5 is the official superseded (newer) version of 3C8-01005-4. They are functionally identical and fully interchangeable. Our gasket replaces both versions.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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