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 (Replaces 27-8637251, 27-860231) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Closed Riser Gasket – Fits MerCruiser GM V6 & V8 5.0L-8.2L (Rep...
Product Details
This Closed Riser Gasket is engineered for MerCruiser stern drives with GM V6 and V8 engines (5.0L to 8.2L, 305-502 CID) used in fresh water cooling systems. It is broadly compatible with models manufactured from approximately 1981 through the early 2000s, providing a reliable seal for closed riser connections.
This part serves as a direct cross-reference for Mercury MerCruiser, Sierra, GLM, OSCO, Mallory, and Barr part numbers, ensuring wide-ranging interchange possibilities.
- Installation Environment: Fresh Water Cooling Systems
- Connection Type: Closed Riser Block Off
- Included: Essential gaskets for a complete replacement
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number |
|---|---|
| Mercury MerCruiser | 27-8637251 |
| Mercury MerCruiser | 27-863725 |
| Mercury MerCruiser | 27-860231 |
| Mercury MerCruiser | 27-41811 |
| Sierra | 18-0672 |
| GLM | 30220 |
| OSCO | 8503-GB |
| Mallory | 9-61422 |
| Barr | MC-47-27-41811 |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure accurate fitment.
This gasket is designed for the following MerCruiser engines. While the list is extensive, always cross-reference your specific OEM part number.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 4.3L | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6 |
| MerCruiser | 4.3LX | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6 |
| MerCruiser | 4.3L LH | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6 |
| MerCruiser | 4.3L LXH | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6 |
| MerCruiser | 4.3L EFI | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6 |
| MerCruiser | 4.3L MPI | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6 |
| MerCruiser | 262 MAG | 175–205 | 4-Stroke | 1987–1995 | 27-8637251 | V6, 4.3L |
| MerCruiser | 200 | 200 | 4-Stroke | 1981–1986 | 27-8637251 | V8, 305 CID |
| MerCruiser | 228 | 228 | 4-Stroke | 1981–1986 | 27-8637251 | V8, 305 CID |
| MerCruiser | 230 | 230 | 4-Stroke | 1981–1986 | 27-8637251 | V8, 305 CID |
| MerCruiser | 230 MIE | 230 | 4-Stroke | 1981–1986 | 27-8637251 | V8, 305 CID |
| MerCruiser | 260 | 260 | 4-Stroke | 1981–1986 | 27-8637251 | V8, 350 CID |
| MerCruiser | 5.0L | 200–260 | 4-Stroke | 1988–1995 | 27-8637251 | V8, 305 CID |
| MerCruiser | 5.0LX | 200–260 | 4-Stroke | 1988–1995 | 27-8637251 | V8, 305 CID |
| MerCruiser | 898 | 200–260 | 4-Stroke | 1983–1984 | 27-8637251 | V8, 305 CID |
| MerCruiser | 5.0L MPI | 200–260 | 4-Stroke | 1988–1995 | 27-8637251 | V8, 305 CID |
| MerCruiser | 5.7L | 250–300 | 4-Stroke | 1988–1995 | 27-8637251 | V8, 350 CID |
| MerCruiser | 7.4L | 330–340 | 4-Stroke | 1988–1995 | 27-8637251 | V8, 454 CID |
| MerCruiser | 8.2L | 380–430 | 4-Stroke | 1988–1995 | 27-8637251 | V8, 502 CID |
| MerCruiser | 350 MAG | 300 | 4-Stroke | 1987–1995 | 27-8637251 | V8, 350 CID |
Technical Specs
- Product Type
- Exhaust Riser Gasket
- Installation
- Fresh Water Cooling System
- Connection
- Closed Riser Block Off
- Material
- Marine Grade Gasket Material
What’s in the Box
- 2 x Closed Riser Gasket (equivalent to 27-8637251)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery.
- Drain the relevant cooling system sections to bring the coolant level below the manifold and riser.
- Carefully remove the bolts securing the exhaust riser to the manifold. Note their lengths and positions if they differ.
- Break the old seal and lift the riser off. It may be heavy; be prepared to support its weight.
- Thoroughly clean both mating surfaces on the manifold and riser. All traces of old gasket material and corrosion must be removed for a proper seal.
- Position the new gasket, ensuring it aligns correctly with all bolt holes and passages.
- Carefully lower the riser back into place.
- Install the mounting bolts and tighten them in a crisscross pattern to the manufacturer's recommended torque specifications. Do not overtighten.
- Refill the cooling system, reconnect the battery, and start the engine.
- Carefully inspect the gasket area for any water or exhaust leaks.
Troubleshooting & FAQ
How do I know if I need a "closed" or "open" riser gasket?
This is a closed, or "block-off," gasket designed for fresh water (closed cooling) systems where antifreeze circulates through the manifold. An open gasket has extra ports to allow raw water to pass through and is used on raw-water cooled engines. Using the wrong type will cause severe engine damage. Always verify your cooling system type.
What are the signs of a failing riser gasket?
Common symptoms include external water leaks (visible drips or steam) around the riser-manifold connection, signs of rust or water trails on the manifold, and, in severe cases, water entering the cylinders. This can cause poor starting, misfires (especially on a cold start), and milky-looking engine oil.
The compatibility chart stops around 1995. Will this fit a newer engine?
The listed years reflect common applications, but part usage often extends beyond these ranges into the early 2000s for certain models. The most reliable way to confirm fitment for a newer engine is to match your original part number to one of the equivalents in our Part Number Matrix.
What is the recommended replacement interval?
There is no fixed interval, but exhaust riser gaskets are typically replaced whenever the exhaust manifolds or risers are serviced. In a salt water environment, this is often every 3-5 years. In fresh water, it can be much longer (7-10+ years). Inspect annually for any signs of leaks or corrosion.
Can I reuse my old riser bolts?
It is strongly recommended to use new bolts, as old ones can be corroded, fatigued, or stretched, leading to improper torque and a failed seal. If reusing bolts, ensure they are clean, in excellent condition, and apply the correct sealant or thread locker per your service manual.
Do I need to use sealant on this gasket?
Most modern gaskets like this are designed to be installed dry. However, some mechanics apply a very thin film of a high-tack, water-resistant sealant to help hold the gasket in place during assembly and to seal minor imperfections on older mating surfaces. Consult your engine's service manual for the official recommendation.
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 and specifications against 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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