Gasket, Water Pump – Fits Mercury/Mariner 75-200hp Outboard (Replaces 27-426311)

$3.50

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This replacement Gasket, Water Pump is designed for a broad range of Mercury and Mariner 2-stroke and 4-stroke outboard engines, from 75hp to 200hp, manufactured between 1982 and 2008. It ensures a proper seal within the water pump assembly to prevent leaks and maintain cooling system efficiency.

This part is a direct replacement for Mercury OEM part numbers 27-426311 and 27-8M0204678, and it also cross-references with Sierra 18-2919, GLM 31050, and Mallory 9-60031.

Installs as a direct replacement for the original part.
Made from durable paper/composite material to withstand the marine environment.
Essential for water pump service and maintenance.

Part Number Matrix

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

Brand	Part Number	Superseded By
Mercury	27-426311	27-8M0204678
Sierra	18-2919
GLM	31050
Mallory	9-60031

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This gasket fits a wide variety of V6 outboards from Mercury and Mariner, including many popular EFI, Magnum, and Pro Max models.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Mercury	V-135, V-150, V-175, V-200	135-200	2-Stroke	1982–1995	27-426311
Mercury	V-150 Magnum/Marathon/Work	150	2-Stroke	1983–1990	27-426311
Mercury	V-1500	150	2-Stroke	1983–1990	27-426311
Mercury	MAGNUM II, MAGNUM III	135-150	2-Stroke	1990–2000	27-426311
Mercury	XR-4, XR-6	150-200	2-Stroke	1990–2004	27-426311
Mercury	EFI Models	135-200	2-Stroke	1995–2006	27-426311
Mercury	150/200 EFI PRO MAX/SUPER MAG	150-200	2-Stroke	1998–2008	27-426311
Mercury	150 Pro XS	150	2-Stroke	2006–2008	27-426311
Mercury	225 EFI PRO MAX/SUPER MAG	225	2-Stroke	1998–2004	27-426311
Mercury	225X EFI PROMAX	225	2-Stroke	2004–2008	27-426311

Technical Specs

Product Type: Water Pump Gasket
Installation: Direct replacement
Fuel Type: Gasoline
Housing Material: Paper/Composite
Product Dimensions: 7.5 in L x 6.0 in W x 0.13 in H
Weight: 0.014 kg (0.03 lb)

What’s in the Box

1 x Gasket (Replaces 27-426311 / 27-8M0204678)

Installation Notes

Disconnect the battery and remove the engine cover.
Drain the lower unit gear lube.
Remove the lower unit (gearcase) from the outboard's driveshaft housing.
Unbolt and remove the water pump housing to access the old gasket and impeller.
Clean both mounting surfaces meticulously, removing all traces of the old gasket material.
Position the new gasket correctly on the cleaned surface.
Reinstall the water pump housing, impeller, and other components, tightening bolts to the manufacturer's specified torque.
Reattach the lower unit, refill with fresh gear lube, and reconnect the battery before testing.

Troubleshooting & FAQ

How do I know if my water pump gasket is failing?

Signs of a failing water pump gasket include visible water leaks around the pump housing, engine overheating at low speeds, or a weak or intermittent water stream from the "telltale" outlet. During routine impeller replacement, always change the gasket.

Will this gasket fit my specific engine model?

This gasket fits a wide range of Mercury/Mariner 75-200hp outboards. Please use the compatibility table on this page to verify your engine's model and year range. Cross-referencing your old part number is the best way to ensure a perfect match.

What is the recommended replacement interval?

It is best practice to replace the water pump gasket whenever you service the water pump impeller, which is typically recommended every 1-2 years or 100-200 hours of use, depending on operating conditions (especially in saltwater or sandy/silty water).

Is any sealant required for this gasket?

Generally, paper gaskets like this one are installed dry on clean, flat surfaces. However, some mechanics apply a very thin, non-hardening sealant as a precautionary measure. Consult your engine's service manual for specific recommendations.

Can an old gasket be reused?

No. Gaskets are single-use components that compress to create a seal. Once removed, they lose their ability to seal effectively and must be replaced to prevent leaks and potential engine damage.

What tools do I need for installation?

You will need a basic marine tool kit, including socket/ratchet sets, screwdrivers, a gasket scraper or plastic razor blade, a torque wrench, and potentially a gear lube pump. Always refer to a service manual for your specific engine.

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.

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