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

$14.00

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Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L (Replaces 27-863725, 27-41811) is backordered and will ship as soon as it is back in stock.

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Product Details

This Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L is specifically engineered for MerCruiser stern drives with GM V6 and V8 engines (5.0L to 8.2L) that use a fresh water (closed) cooling system. It is designed for compatibility with models produced from approximately 1981 through the early 2000s that feature a center rise outlet exhaust manifold.

This part is a direct replacement for multiple OEM and aftermarket part numbers, including Mercury MerCruiser 27-863725, 27-41811, 27-860231, Sierra 18-0672, and others.

Engineered for closed-riser (fresh water cooling) systems.
Connects the exhaust manifold to the center rise outlet.
Package includes two gaskets for a complete installation.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury MerCruiser	27-863725 / 27-8637251
Mercury MerCruiser	27-41811
Mercury MerCruiser	27-860231
Sierra	18-0672
Barr	MC-20-87918 / MC-47-27-41811
GLM	30220
OSCO	8503-GB
Mallory	9-61422
UANOFCN	863725

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For MerCruiser applications, this gasket fits a wide range of V6 and V8 models from the early 1980s to the mid-1990s and beyond, as detailed in the compatibility list.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
MerCruiser	4.3L	175–205	4-Stroke	1987–1995	27-863725	V6
MerCruiser	4.3LX	175–205	4-Stroke	1987–1995	27-863725	V6
MerCruiser	4.3L LH	175–205	4-Stroke	1987–1995	27-863725	V6
MerCruiser	4.3L LXH	175–205	4-Stroke	1987–1995	27-863725	V6
MerCruiser	4.3L EFI	175–205	4-Stroke	1987–1995	27-863725	V6
MerCruiser	4.3L MPI	175–205	4-Stroke	1987–1995	27-863725	V6
MerCruiser	262 MAG	175–205	4-Stroke	1987–1995	27-863725	V6, 4.3L
MerCruiser	200	200	4-Stroke	1981–1986	27-863725	V8, 305 CID
MerCruiser	228	228	4-Stroke	1981–1986	27-863725	V8, 305 CID
MerCruiser	230	230	4-Stroke	1981–1986	27-863725	V8, 305 CID
MerCruiser	230 MIE	230	4-Stroke	1981–1986	27-863725	V8, 305 CID
MerCruiser	260	260	4-Stroke	1981–1986	27-863725	V8, 350 CID
MerCruiser	5.0L	200–260	4-Stroke	1988–1995	27-863725	V8, 305 CID
MerCruiser	5.0LX	200–260	4-Stroke	1988–1995	27-863725	V8, 305 CID
MerCruiser	898	200–260	4-Stroke	1983–1984	27-863725	V8, 305 CID
MerCruiser	5.0L MPI	200–260	4-Stroke	1988–1995	27-863725	V8, 305 CID
MerCruiser	5.7L	250–300	4-Stroke	1988–1995	27-863725	V8, 350 CID
MerCruiser	7.4L	330–340	4-Stroke	1988–1995	27-863725	V8, 454 CID
MerCruiser	8.2L	380–430	4-Stroke	1988–1995	27-863725	V8, 502 CID
MerCruiser	350 MAG	300	4-Stroke	1987–1995	27-863725	V8, 350 CID

Technical Specs

Product Type: Exhaust Riser Gasket
Installation: Closed-Riser (Fresh Water Cooling System)
Connection: Center Rise Outlet Exhaust Manifold
Material: Marine-Grade Gasket Material
Other Technical Attributes: For use with center rise outlet exhaust manifold in closed cooling systems

What’s in the Box

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

Installation Notes

Disconnect the battery and allow the engine to cool completely before starting.
Drain the engine coolant from the closed cooling system to a level below the exhaust manifold.
Carefully disconnect any hoses or sensors attached to the exhaust riser.
Remove the mounting bolts that secure the riser to the manifold. Note their length and position for reassembly.
Gently break the seal and lift the riser off the manifold. Be prepared for some residual coolant spillage.
Thoroughly clean both the manifold and riser mating surfaces. All old gasket material and corrosion must be removed for a proper seal.
Place the new gasket onto the manifold, ensuring it is correctly aligned with the bolt holes and passages.
Carefully lower the riser back into position and start the bolts by hand to prevent cross-threading.
Tighten the bolts in a crisscross pattern to the manufacturer’s specified torque. Do not overtighten.
Reconnect all hoses and sensors, refill the cooling system, and reconnect the battery.
Start the engine and check for any exhaust or coolant leaks around the new gasket.

Troubleshooting & FAQ

How do I confirm this gasket fits my engine?

First, verify that your engine has a fresh water (closed) cooling system. Second, check your engine model and year against the compatibility table provided. Finally, cross-reference your existing part number with the numbers in our Part Number Matrix.

What is the difference between a closed riser gasket and an open one?

A closed riser gasket, like this one, is designed for fresh water cooling systems where engine coolant circulates through the manifold and riser. It has no large raw water passage. An open gasket has large ports to allow raw water to pass through, used in raw water cooled systems.

What are the signs of a failing riser gasket?

Common symptoms include water leaking externally from the joint between the manifold and riser, water in the engine oil (milky oil), steam from the engine compartment, or engine overheating. A compromised gasket can lead to catastrophic engine damage if not addressed.

How often should riser gaskets be replaced?

Riser and manifold gaskets should be inspected annually and are typically replaced every 3-5 years in saltwater environments or 5-7 years in freshwater, as part of regular exhaust system maintenance.

Do I need to use sealant with this gasket?

Generally, these gaskets are designed to be installed dry. Applying sealant can sometimes interfere with proper sealing. Always follow the specific instructions in your engine's service manual.

Can I reuse my old riser bolts?

It is strongly recommended to use new bolts when replacing exhaust components. Old bolts can suffer from corrosion and fatigue, potentially leading to incorrect torque or failure.

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

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Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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