Gasket – Mercury-Mariner 4-6 HP (Replaces 27-803508, 803508, 3H6-01005-1)
Gasket – Mercury-Mariner 4-6 HP (Replaces 27-803508, 803508, 3H6-01005-1) is backordered and will ship as soon as it is back in stock.
Couldn't load pickup availability
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
Gasket – Mercury-Mariner 4-6 HP (Replaces 27-803508, 803508, 3H6-01...
Product Details
This Gasket – Mercury-Mariner 4-6 HP is a direct-fit replacement cylinder head gasket for Mercury, Mariner, and Tohatsu/Nissan 4, 5, and 6 HP 4-stroke outboard engines manufactured from 1999 to the current model year, including Japanese-built (JCI) models. It ensures a reliable seal for optimal engine performance and longevity.
This part is a direct replacement for Mercury-Mercruiser part number 27-803508, Tohatsu-Nissan 3H6-01005-1, and GLM 36330, offering a precise interchange for multiple OEM and aftermarket references.
- Engineered to meet or exceed original factory specifications.
- Provides a robust seal for the cylinder head assembly.
- Compatible with a wide range of Mercury, Mariner, and Tohatsu models.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury-Mercruiser | 27-803508 |
| Tohatsu-Nissan | 3H6-01005-1 |
| GLM | 36330 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercury/Mariner owners: This gasket fits specific 4-stroke outboards from 4 to 6 HP manufactured since 1999. Please verify your engine's serial number range against the table to ensure an exact match.
For Tohatsu owners: This part fits Japanese-made 4, 5, and 6 HP 4-stroke engines from 1999 and newer.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 4 (4-Stroke) | 4 | 4-Stroke | 0P073456 Thru 0P400999, 0P401000 Thru 0R411837, 0R000001 Thru 0R067089, 0R067090 Thru 0R411837, 0R411838 & Up | 27-803508 | |
| Mercury | 5 (4-Stroke) | 5 | 4-Stroke | 0P073456 Thru 0P400999, 0P401000 Thru 0R411837, 0R000001 Thru 0R067089, 0R067090 Thru 0R411837, 0R411838 & Up | 27-803508 | |
| Mercury | 5 (4-Stroke) JCI | 5 | 4-Stroke | 0R560794 & Up | 27-803508 | |
| Mercury | 6 (4-Stroke) | 6 | 4-Stroke | 0P073456 Thru 0P400999, 0P401000 Thru 0R411837, 0R000001 Thru 0R067089, 0R067090 Thru 0R411837, 0R411838 & Up | 27-803508 | |
| Tohatsu | 4 HP | 4 | 4-Stroke | 1999 & Up | 3H6-01005-1 | Made in JPN |
| Tohatsu | 5 HP | 5 | 4-Stroke | 1999 & Up | 3H6-01005-1 | Made in JPN |
| Tohatsu | 6 HP | 6 | 4-Stroke | 1999 & Up | 3H6-01005-1 | Made in JPN |
| Mariner | 4 (4-Stroke) | 4 | 4-Stroke | 1999 & Up | 27-803508 | Made in JPN |
| Mariner | 5 (4-Stroke) | 5 | 4-Stroke | 1999 & Up | 27-803508 | Made in JPN |
| Mariner | 6 (4-Stroke) | 6 | 4-Stroke | 1999 & Up | 27-803508 | Made in JPN |
Technical Specs
- Product Type
- Gasket, Cylinder Head
- Dimensions
- 15.0 in x 14.0 in x 0.5 in
- Weight
- 0.027 kg (0.06 lb)
- Other Technical Attributes
- Genuine Mercury Marine factory OEM part; also fits Tohatsu.
What’s in the Box
- 1 x GASKET (27-803508)
Installation Notes
The following are general, model-agnostic guidelines. Always consult your engine's official service manual for detailed procedures and torque specifications.
- Disconnect the battery and ensure the engine is cool. Drain the cooling system.
- Remove the engine cover and any components obstructing access to the cylinder head, such as the intake and exhaust manifolds.
- Carefully loosen the cylinder head bolts in the reverse order of the tightening sequence specified in your service manual.
- Lift the cylinder head off the engine block. If it's stuck, gently tap it with a soft mallet; do not pry between the mating surfaces.
- Remove the old head gasket and thoroughly clean both the cylinder head and engine block surfaces of any old gasket material, sealant, or carbon buildup.
- Place the new gasket onto the engine block, ensuring it is correctly oriented. Do not use any sealant unless explicitly required by the manufacturer.
- Carefully lower the cylinder head back into place over the alignment dowels.
- Install and tighten the head bolts in the sequence and torque stages specified in your service manual to ensure an even, leak-free seal.
- Reassemble all previously removed components. Refill the cooling system.
- Reconnect the battery. Start the engine and check for any compression, oil, or coolant leaks around the head gasket.
Troubleshooting & FAQ
How do I know if this gasket fits my engine?
The most reliable method is to check your Mercury/Mariner engine's serial number or your Tohatsu's model and year. Compare this information with the "Engine & Model Compatibility" table. If your engine is listed, the part is a confirmed fit.
What are the signs of a failed head gasket?
Common symptoms include engine overheating, loss of power, white smoke from the exhaust (coolant burning), milky or foamy engine oil (oil and coolant mixing), or visible coolant/oil leaks from the seam between the cylinder head and engine block.
Is any sealant required when installing this gasket?
Most modern head gaskets, including this one, 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 follow the specific instructions in your engine's service manual.
How often should a head gasket be replaced?
A head gasket is not a routine maintenance item. It is designed to last the life of the engine and should only be replaced if it fails or during a major engine rebuild that requires removing the cylinder head.
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.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
