Thermostat Repair Service Kit – Fits Mercury 75-120 HP Outboards & SportJet 90-120 HP (Replaces F664068, 859620, 828319, F476067)

$35.99 $57.00

Shipping calculated at checkout.

Thermostat Repair Service Kit – Fits Mercury 75-120 HP Outboards & SportJet 90-120 HP (Replaces F664068, 859620, 828319, F476067) is backordered and will ship as soon as it is back in stock.

Worry-free returns

You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.

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 Repair Service Kit – Fits Mercury 75-120 HP Outboards & SportJet 90-120 HP provides a complete solution for maintaining the correct engine operating temperature in compatible Mercury/Mariner, Force, and SportJet models. Designed to operate at 130°F (54°C), it ensures your engine runs efficiently, preventing overheating and improving performance across a range of model years from 1990 to 1999.

It serves as a direct replacement for Mercury part numbers F664068, 859620, 828319, and F476067, as well as aftermarket equivalents like Sierra 18-0854.

Engineered for direct OEM-replacement installation without modifications.
Maintains a consistent operating temperature of 130°F (54°C) for optimal engine health.
Includes the thermostat, housing gasket, and seal for a complete service.

Part Number Matrix

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

Brand	Part Number
Mercury	F664068
Mercury	859620
Mercury	828319
Mercury	F476067
Sierra	18-0854
JUWEVAZU	F664068
GHmarine	F664068

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	Outboard	75	2-Stroke	1998–1999	F664068	Serial Range: 0E288000-0E344999, 0E345000-0E369299
Mercury	Outboard	90	2-Stroke	1990–1992	F664068	Serial Range: 1991E-1992C
Mercury	Outboard	90	2-Stroke	1990–1994	F664068	Serial Range: 0E000001-0E093699
Mercury	Outboard	90	2-Stroke	1990	F664068	Multiple serial ranges including 903X90A-Up, 906A90A-Up, 906F90A-Up
Mercury	Outboard	90	2-Stroke	1996–1997	F664068	Serial Range: 0E138600-0E202999, 0E203000-0E287999
Mercury	Outboard	90	2-Stroke	1999	F664068	Serial Range: 0E345000-0E369299
Mercury	Outboard	120	2-Stroke	1995	F664068	Serial Range: 0E093700-0E138599
Mercury	Outboard	120	2-Stroke	1996–1997	F664068	Serial Range: 0E138600-0E202999, 0E203000-0E287999
Force	Outboard	70, 75, 85, 90, 120, 125, 150	2-Stroke	1990–1999	F664068	As referenced in JLM Marine catalog
Mercury	SportJet	90	2-Stroke	1993	F664068	Non-Oil Injection, Powerhead: Serial Range 0E023150-0E033710
Mercury	SportJet	90	2-Stroke	1993	F664068	Jet Drive: Serial Range 0E021000-0E036999
Mercury	SportJet	90	2-Stroke	1994	F664068	Non-Oil Injection, Powerhead: Serial Range 0E033711-0E066619
Mercury	SportJet	90	2-Stroke	1994	F664068	Oil Injection, Powerhead: Serial Range 0E066620-0E095087
Mercury	SportJet	95XR	2-Stroke	1996	F664068	Powerhead: Serial Range 0E141089-0E202999
Mercury	SportJet	95XR	2-Stroke	1996	F664068	Jet Drive: Serial Range 0E145580-0E151579
Mercury	SportJet	95XR	2-Stroke	1997	F664068	Powerhead: Serial Range 0E203000-0E315904
Mercury	SportJet	95XR	2-Stroke	1997	F664068	Jet Drive: Serial Range 0E151580-0E288445
Mercury	SportJet	120	2-Stroke	1995	F664068	Powerhead: Serial Range 0E095088-0E141088
Mercury	SportJet	120	2-Stroke	1995	F664068	Jet Drive: Serial Range 0E080400-0E145579

Technical Specs

Product Type: Thermostat Kit with Gasket and Seal
Installation: Direct OEM replacement
Housing Material: Metal
Housing Color: Brass/Gray
Operating Temperature: 130°F (54°C)
Warranty: 1-year against manufacturing defects

What’s in the Box

1 x Thermostat (F664068)
1 x Thermostat Housing Gasket (828319)
1 x Thermostat Seal (F664914)

Installation Notes

Disconnect the battery and ensure the engine is cool before beginning.
Locate the thermostat housing on the engine block or cylinder head and place a drain pan beneath it.
Carefully remove the bolts securing the housing cover. Note the orientation of all parts.
Remove the old thermostat, gasket, and seal. You may need to gently pry them out.
Thoroughly clean the mating surfaces of the housing and cover, removing all old gasket material and corrosion.
Install the new thermostat, ensuring it is seated in the correct direction. Place the new seal and gasket in position.
Re-install the housing cover and tighten the bolts to the manufacturer's recommended torque specification.
Refill the cooling system, check for leaks, and run the engine to verify proper operation and temperature regulation.

Troubleshooting & FAQ

How do I know if this thermostat kit will fit my engine?

Verify your engine model, horsepower, and year against the compatibility tables. Pay close attention to any serial number ranges provided in the "Notes" column, as they are critical for confirming a match. Cross-referencing your old part number with our "Part Number Matrix" is also a reliable method.

What are the signs of a failing thermostat?

Common symptoms include the engine overheating at low speeds, running too cold at cruising speeds, erratic temperature gauge readings, or a noticeable increase in fuel consumption. A thermostat can fail by sticking open or sticking closed, each causing different issues.

What temperature does this thermostat operate at?

This thermostat is designed to open and maintain a consistent engine operating temperature of 130°F (54°C), which is the standard specification for the listed engine models to ensure optimal performance and longevity.

How often should a marine thermostat be replaced?

As a preventative maintenance measure, it's wise to inspect the thermostat during any major cooling system service (like a water pump impeller change) and replace it every 2-3 years or 200-300 hours, especially if operating in saltwater.

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.

Payment & Security

Payment methods

Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.