Water Pump Base Gasket – Fits Mercury/Mariner 75–200HP (Replaces 27-856704)

$3.44

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Product Details

This aftermarket Water Pump Base Gasket provides a crucial seal between the water pump base and the gear housing for Mercury and Mariner outboards. Designed for a wide range of 75–200HP 2-stroke models from the 1980s and 1990s, it also fits select 4-stroke engines and Alpha One (Gen 1) stern drives. It ensures a direct-fit replacement for a leak-free repair during routine water pump service.

This part is a direct replacement for Mercury/Mariner OEM part numbers 27-856704, 27-85610, 27-856101, and 27-33146, as well as Quicksilver 27-856704.

Engineered for direct-fit installation during water pump service.
Constructed from durable, compression-fit paper/fiber-based gasket material.
Creates a reliable seal to prevent water leaks and maintain cooling system pressure.

Part Number Matrix

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

Brand	Part Number	Superseded By
Mercury / Mariner / Quicksilver	27-856704	27-8M0214962
Mercury / Mariner	27-85610
Mercury / Mariner	27-856101
Mercury / Mariner	27-33146

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Fitment for Mercury and Mariner outboards is primarily determined by engine serial number. Please verify your number falls within the specified ranges.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Mercury	75 (4 CYL.)	75	2-Stroke	6432901 & Up	27-856704
Mercury	75 (4 CYL.)	75	2-Stroke	7208573 & Up	27-856704
Mercury	75 (4 CYL.)	75	2-Stroke	9393856 & Up	27-856704
Mercury	90, 900 (6 CYL.)	90	2-Stroke	6436123 & Up	27-856704
Mercury	90, 900 (6 CYL.)	90	2-Stroke	7208848 & Up	27-856704
Mercury	115 (6 CYL.)	115	2-Stroke	6436123 & Up	27-856704
Mercury	115 (6 CYL.)	115	2-Stroke	7208848 & Up	27-856704
Mercury	V-150-XR-2	150	2-Stroke	4868998–0A904645	27-856704
Mercury	V-150	150	2-Stroke	4868998–0A904645	27-856704
Mercury	V-150 Magnum	150	2-Stroke	5600162–0A904645	27-856704
Mercury	V-150 Marathon	150	2-Stroke	5600162–0A904645	27-856704
Mercury	V-150 Work	150	2-Stroke	4868998–0A904645	27-856704
Mercury	V-1500	150	2-Stroke	4868998–0A904645	27-856704
Mercury	V-175	175	2-Stroke	4301235–0C100860	27-856704
Mercury	V-175	175	2-Stroke	8058870 & Up	27-856704
Mercury	V-200	200	2-Stroke	5239232–0C100860	27-856704

This gasket is also used in MerCruiser R/MR/Alpha One stern drive and transom assemblies from 1983–1990.

Brand	Model	Years	OEM Part No.	Notes
MerCruiser	R/MR/ALPHA ONE (Sterndrive)	1983–1990	27-856704	Serial: 6225577–0F386995
MerCruiser	R/MR/ALPHA ONE (Transom Assembly)	1983–1990	27-856704	Serial: 6216687–0F386995

Technical Specs

Product Type: Water Pump Base to Gear Housing Gasket
Application: Used between water pump base and gear housing
Installation: Direct Fit, Replace during water pump service
Fitting Type: Compression Gasket
Housing Material: Paper/Fiber-based gasket material
Housing Color: Tan/Brown (typical gasket color)
Dimensions: 7.5" L x 6.0" W x 1.06" H

What’s in the Box

1 x GASKET (Replaces 27-856704)

Installation Notes

Ensure the engine is off and the battery is disconnected. Place the drive in neutral.
Drain the gearcase lube completely from the lower unit.
Remove the nuts or bolts securing the lower unit (gearcase) to the midsection and carefully lower it.
Unbolt and remove the old water pump housing, impeller, and base plate.
Thoroughly clean all mating surfaces, removing any old gasket residue, sealant, or corrosion.
Position the new water pump base gasket onto the clean gear housing surface.
Reassemble the water pump with new components (impeller, wear plate, etc.) as needed.
Reinstall the lower unit, ensuring the shift shaft and driveshaft align correctly. Torque bolts to manufacturer specs.
Refill the gearcase with fresh, recommended marine gear lube.
Reconnect the battery. Start the engine using a water supply (flushing muffs) and verify water is exiting the tell-tale port.

Troubleshooting & FAQ

How do I know this gasket is the right one for my engine?

The best way to confirm fitment is by matching your engine's serial number to the ranges listed in the compatibility tables. While many models are covered, serial number is the most accurate check. If in doubt, compare the shape of this gasket in the photos to your old one before purchase.

What are the signs of a failed water pump base gasket?

A failed base gasket can cause a water leak into the gearcase (milky gear lube), an external water leak around the pump base, or a loss of cooling water pressure, which can lead to engine overheating at idle or low speeds.

Can I reuse my old gasket?

No. This is a single-use compression gasket. It should be replaced every time the water pump is serviced to ensure a proper, leak-free seal. Reusing an old gasket will likely result in leaks and potential engine damage.

The data says this fits 2-stroke and some 4-stroke models. How do I know if it fits my 4-stroke?

While this part is predominantly for the 2-stroke V6 and L4/L6 models listed, it has some crossover application with early 4-strokes that share the same gearcase design. We do not have a comprehensive list for 4-stroke models; please verify your OEM part number is 27-856704 before ordering for a 4-stroke engine.

What is the difference between 27-856704 and the superseded part 27-8M0214962?

Superseded parts are updated versions from the original manufacturer. Functionally, they are interchangeable. This aftermarket listing is manufactured to meet or exceed the specifications for the original 27-856704 part number.

My engine's serial number isn't listed, but the model and year seem to match. Will it fit?

It might, but we cannot guarantee it. Manufacturers often make mid-year changes based on serial number breaks. If your serial number is not in the specified range, we strongly advise against purchasing without first confirming the required part number through an OEM parts diagram 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

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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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