Thermostat Cover Gasket - Fits Mercury/Mariner 30-60 HP 3-Cylinder Outboards (Replaces 27-827284)

$4.59

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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 Thermostat Cover Gasket is engineered for Mercury/Mariner 30-60 HP, 3-cylinder, 2-stroke outboard models manufactured from 1987 through the early 2000s. It creates a secure seal for the thermostat housing to prevent coolant leaks and ensure proper engine operating temperature.

It serves as a direct replacement for Mercury/Quicksilver part number 27-827284 and provides an interchange for Sierra 18-2721 and GLM 37850.

Designed for direct-fit installation.
Ensures a reliable seal within the engine's cooling system.
Meets or exceeds OEM specifications for fit and function.

Part Number Matrix

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

Brand	Part Number
Mercury/Quicksilver	27-827284 / 827284
Sierra	18-2721
GLM	37850

Engine & Model Compatibility

Confirm your engine model and year in the table below to ensure accurate fitment.

This gasket fits a range of 3-cylinder Mercury and Mariner outboards. Please verify your specific model and serial number, as manufacturing years can have variations.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury/Mariner	30 JET	30	2-Stroke	1987–1999	27-827284	3-cylinder models
Mercury/Mariner	40	40	2-Stroke	1987–2005	27-827284	3-cylinder models
Mercury/Mariner	40 JET	40	2-Stroke	1987–2005	27-827284	Models through serial break
Mercury/Mariner	45 JET	45	2-Stroke	1987–2005	27-827284	Models through serial break
Mercury/Mariner	50	50	2-Stroke	1987–2005	27-827284	3-cylinder models
Mercury/Mariner	55	55	2-Stroke	1987–2005	27-827284	3-cylinder models
Mercury/Mariner	60	60	2-Stroke	1987–2005	27-827284	3-cylinder models
Mercury/Mariner	60 BIGFOOT	60	2-Stroke	1987–1999	27-827284	3-cylinder models

Technical Specs

Product Type: Thermostat Cover Gasket
Installation: Direct replacement
Dimensions: 11.0 × 10.0 × 0.5 in (approx. 279 × 254 × 13 mm)
Weight: 9.07 g (0.02 lb)
Warranty: Varies by manufacturer (Sierra: Lifetime limited warranty)

What’s in the Box

1 x Thermostat Cover Gasket (Replaces 27-827284)

Installation Notes

Allow the engine to cool completely before starting. Disconnect the battery.
Locate the thermostat housing on the engine.
Drain coolant to a level below the housing or as specified by your service manual.
Remove the cover bolts and carefully pry the cover off.
Remove the old gasket and thoroughly clean both mating surfaces. Scrape away any residual material.
Position the new gasket correctly on the housing.
Reinstall the cover and tighten the bolts to the manufacturer's specified torque, typically in a crisscross pattern.
Refill the cooling system, start the engine, and carefully inspect for any leaks as it warms up.

Troubleshooting & FAQ

How do I know if this gasket will fit my exact engine model?

This gasket fits most Mercury/Mariner 30-60 HP 3-cylinder 2-stroke outboards from 1987 to the early 2000s. The most reliable way to confirm fitment is to match your existing part number to 27-827284 or the aftermarket cross-references provided. Also, check the compatibility table on this page.

What are the signs of a failed thermostat cover gasket?

Common signs include visible coolant leaks (greenish fluid) around the thermostat housing, engine overheating alarms or high temperature gauge readings, and excessive white steam from the exhaust.

Is any sealant required for this gasket?

Generally, new gaskets of this type are designed to be installed on clean, dry surfaces without sealant. However, always consult your engine's official service manual for model-specific instructions, as recommendations can vary.

How often should this gasket be replaced?

It is best practice to replace the thermostat gasket anytime the thermostat is replaced, the cooling system is serviced, or if you notice any leaks or damage in the housing area.

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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