Thermostat Kit – Fits Mercury Marine MerCruiser Engines (Replaces 338884)

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Product Details

This Thermostat Kit – Fits Mercury Marine MerCruiser Engines (Replaces 338884) is engineered to regulate engine temperature for optimal performance in a wide range of Mercury Marine and MerCruiser gasoline stern drive and inboard engines from 1974 to 2021, including 3.0L to 8.2L models.

It serves as a direct replacement for Mercury 338884, Sierra 18-3562, GLM 13371, Mallory 9-13009, and Quicksilver 338884, ensuring a precise fit and reliable function.

Installs directly into the engine's cooling system.
Opens at a consistent 142°F (61.1°C) to maintain proper operating temperature.
Includes the necessary thermostat, gasket, and mounting bolts for a complete installation.

Part Number Matrix

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

Brand	Part Number
Mercury	338884
Mercury	46-338884
Quicksilver	338884
Sierra	18-3562
GLM	13371
Mallory	9-13009

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For MerCruiser models, this thermostat fits a wide variety of inline, V6, and V8 gasoline engines. For Mercury outboards, it is specific to V6 and V8 models from 1994 onwards.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
MerCruiser	3.0L (181 CID)	130–140	4-Stroke	1990–2015	338884
MerCruiser	4.3L (262 CID)	180–220	4-Stroke	1986–2021	338884
MerCruiser	5.0L (305 CID)	220–260	4-Stroke	1983–2021	338884
MerCruiser	5.7L (350 CID)	220–350	4-Stroke	1974–2021	338884
MerCruiser	6.2L (377 CID)	300–350	4-Stroke	2015–2021	338884
MerCruiser	7.4L (454 CID)	310–385	4-Stroke	1991–2001	338884
MerCruiser	8.2L (502 CID)	380–430	4-Stroke	1991–2018	338884
Mercury	200–350 HP Outboards	200–350	4-Stroke	1994–2021	338884	V6 and V8 models only

Technical Specs

Product Type: Thermostat Kit
Installation: Engine Cooling System
Operating Temperature: 142°F (61.1°C) Opening Temperature
Connection: Direct OEM Replacement
Housing Material: Stainless Steel / Brass
Housing Color: Metallic
Product Dimensions: 6.0 x 7.13 x 1.25 inches
Weight: 0.23 kg (0.5 lb)
Other Technical Attributes: Includes Gasket and Mounting Hardware
Warranty: 1-Year Limited Warranty

What’s in the Box

1 x Thermostat (338884)
1 x Gasket (27-835844)
2 x Mounting Bolts

Installation Notes

Ensure the engine is completely cool. Disconnect the boat's battery for safety.
Place a drain pan beneath the engine's heat exchanger or thermostat housing and drain the coolant.
Locate the thermostat housing. It is typically on top of the engine where the main coolant hose connects.
Remove the bolts securing the housing cover. You may need to gently tap the cover to break the seal.
Note the orientation of the old thermostat before removing it and its gasket.
Thoroughly clean both mating surfaces of the housing and its cover, removing all old gasket material.
Install the new thermostat in the correct orientation, followed by the new gasket.
Reinstall the housing cover and tighten the bolts to the manufacturer-specified torque. Do not overtighten.
Reconnect all hoses, refill the cooling system with the appropriate coolant, and reconnect the battery.
Start the engine and let it warm up, carefully checking for any leaks around the thermostat housing.

Troubleshooting & FAQ

How do I know if my thermostat has failed?

Common signs of a failed thermostat include the engine overheating (stuck closed) or taking too long to reach operating temperature (stuck open). You may see corresponding alarms on your gauges or notice poor performance.

Will this thermostat fit my specific engine model?

This kit is designed for a broad range of MerCruiser and Mercury engines as listed in the compatibility table. Always verify your engine's model and year range against the table. If you are unsure, check your engine's service manual or part number.

Is the gasket included in this kit?

Yes, this is a complete kit that includes the thermostat, a new gasket, and two mounting bolts, providing everything needed for a standard replacement.

What is the correct operating temperature for this thermostat?

This thermostat is designed to begin opening at 142°F (61.1°C), which is the standard temperature for the specified raw water-cooled engine models.

How often should a marine thermostat be replaced?

While there's no fixed interval, it is good practice to inspect the thermostat every few years or 200-300 hours. It is often replaced as preventative maintenance, especially if the boat is used in saltwater, which can accelerate corrosion.

What's the difference between an OEM part and an aftermarket one?

This listing is an aftermarket replacement (not OEM). It has been engineered and manufactured to meet or exceed original equipment specifications in terms of fit, form, and function. Our parts are produced in an ISO 9002 certified facility and undergo batch inspections to ensure quality and consistency.

How fast is shipping and what does it cost?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free on all orders. Expedited shipping options and associated costs, if available for your location, will be displayed at checkout.

What is the warranty and return policy?

This product is covered by a 1-year warranty against manufacturing defects under normal marine use. If you encounter an issue, please contact our support team with your order number. Returns are accepted within our standard return window for unused items in their original packaging. Please see our policy page or contact us for detailed 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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