Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L (Replaces 27-863725, 27-41811)

Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L (Replaces 27-863725, 27-41811)

This closed riser gasket is engineered for MerCruiser stern drives equipped with GM V6 and V8 engines (5.0L to 8.2L) that feature a fresh water (closed) cooling system. It is compatible with models produced from approximately 1981 through the early 2000s that use a center rise outlet exhaust manifold.

This part is a direct replacement for Mercury MerCruiser part numbers 27-863725, 27-8637251, 27-41811, and 27-860231.

• For Closed Cooling Systems: Specifically designed for engines with fresh water cooling.
• Marine-Grade Material: Constructed from durable materials to ensure a reliable, long-lasting seal in harsh marine environments.
• Package Contents: Includes 2 x Closed Riser Gaskets.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 2 x Closed Riser Gasket (Replaces OEM 27-863725 / 27-8637251)

Installation Guide

1. Safety First: Disconnect the battery and ensure the engine is cool to the touch before starting any work.
2. Drain Coolant: Drain the coolant from the closed cooling system to a level below the exhaust manifold.
3. Remove Hoses: Carefully disconnect any hoses attached to the exhaust riser. Be prepared for some residual fluid spillage.
4. Unbolt the Riser: Loosen and remove the bolts securing the riser to the exhaust manifold. The riser may be heavy, so support its weight as you remove the last bolt.
5. Remove Old Gasket: Lift the riser away from the manifold and remove the old gasket.
6. Clean Mating Surfaces: Thoroughly clean both the manifold and riser mating surfaces. Use a gasket scraper or wire brush to remove all traces of old gasket material and corrosion.
7. Position New Gasket: Place the new closed riser gasket onto the exhaust manifold, ensuring it aligns correctly with the bolt holes and water passages.
8. Reinstall Riser: Carefully place the riser back onto the manifold, making sure not to dislodge the new gasket.
9. Torque Bolts: Insert and hand-tighten the mounting bolts. Then, use a torque wrench to tighten the bolts to the manufacturer's specified torque sequence and values.
10. Reconnect Hoses & Refill: Reattach all hoses securely and refill the cooling system with the appropriate coolant.
11. Check for Leaks: Reconnect the battery. Start the engine and let it run for several minutes, carefully checking for any water or exhaust leaks around the gasket.

Troubleshooting & FAQ

Q: How do I confirm this gasket fits my engine?

This gasket is for MerCruiser GM V6 and V8 engines with a fresh water (closed) cooling system and a center-rise exhaust manifold. It is critical to verify your cooling system type. If you have a raw water (open) cooling system, you will need a different gasket (open/restricted type). Cross-reference your existing part number with our list and check your engine model in the compatibility table.

Q: What are the common signs of a failing riser gasket?

Symptoms of a bad riser gasket include water leaking externally from the joint between the riser and manifold, engine overheating, or, in severe cases, water entering the engine cylinders (which can cause hydrostatic lock and catastrophic failure). White steam from the exhaust and a milky appearance in the engine oil are also critical warning signs.

Q: How often should I replace my exhaust riser gaskets?

Replacement intervals depend on usage and operating conditions (saltwater vs. freshwater). As a general rule, it's good practice to inspect exhaust manifolds and risers every 3-5 years in saltwater environments and 5-7 years in freshwater. Gaskets should be replaced whenever the risers are removed for inspection or service.

Q: OEM vs. Aftermarket?

This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?

We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?

This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.