Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L (Replaces 27-8637251, 27-860231)

Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L

This closed riser gasket is engineered for MerCruiser stern drives equipped with GM V6 and V8 engines (5.0L to 8.2L / 305-502 CID) featuring fresh water cooling systems. It is compatible with models produced from approximately 1981 through the early 2000s.

It serves as a direct replacement for MerCruiser part numbers 27-8637251, 27-860231, and 27-41811, ensuring a precise fit and reliable seal for your marine engine's exhaust system.

• Installation Type: Designed specifically for closed-riser applications in fresh water cooling systems.
• Material: Constructed from high-quality, marine-grade gasket material to resist heat and corrosion.
• Package Contents: Includes two gaskets for a complete installation or to keep a spare on hand.

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 27-8637251)

Installation Guide

1. Ensure the engine is cool and the battery is disconnected. Drain the cooling system to a level below the exhaust riser.
2. Carefully unbolt and remove the exhaust riser from the exhaust manifold.
3. Remove the old gasket completely. Thoroughly clean both mating surfaces, ensuring they are free of any old gasket material, scale, or debris.
4. Position the new closed riser gasket onto the manifold, ensuring correct alignment.
5. Reinstall the riser and tighten the bolts in the sequence and to the torque values specified by the manufacturer.
6. Refill the engine's fresh water cooling system.
7. Reconnect the battery, start the engine, and carefully inspect for any water or exhaust leaks around the riser joint.

Troubleshooting & FAQ

How do I confirm this gasket fits my engine?

This gasket is for MerCruiser V6 and V8 engines (5.0L to 8.2L) from approximately 1981 to the early 2000s used in fresh water cooling systems. Please check the "Compatible Engine Models" table and cross-reference your OEM part number (e.g., 27-8637251, 27-860231) to ensure a perfect match.

What is a "closed" riser gasket and why is it important?

This is a "closed" or "block off" style gasket, meaning it does not have open passages for raw water to flow between the manifold and riser. It is specifically designed for engines with fresh water (closed) cooling systems. Using the wrong type of gasket (e.g., an open one on a closed system) can lead to severe engine damage.

What are the signs that my riser gasket needs replacing?

Common signs of a failed riser gasket include water leaking externally from the joint between the riser and manifold, water in the engine oil (milky appearance), or excessive steam from the exhaust. It's recommended to inspect gaskets as part of regular marine engine maintenance.

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.

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.

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.