Thermostat Kit 825212 18-3642 130F 54C for Mercury Mariner 8 9.9 15 25 30 40 45 50 HP
Thermostat Kit 825212 18-3642 130F 54C for Mercury Mariner 8 9.9 15 25 30 40 45 50 HP
Product Overview
Thermostat kit for Mercury and Mariner four stroke outboards from 8 HP to 50 HP, the 130 degree Fahrenheit, 54 degree Celsius thermostat 825212 with its rubber ring and cover gasket in one package. It replaces 825212, 825212001, 825212T02 and 855676003, crosses to Sierra 18-3642, and it ships in a 15 x 10 x 3 cm pack.
It fits the 8 HP built from 2001 to 2004, the 9.9 HP from 1999 to 2004, the 15 HP from 1999 to 2006, the 25 HP and 30 HP from 1999 to 2005, the 40 HP from 1999 to 2014, the 45 HP from 1996 to 2000 and the 50 HP from 1995 to 2000. Those are the small and mid range four strokes that do most of the work on rivers, lakes and inshore boats.
A thermostat that sticks open keeps the motor cold, which fouls plugs, washes the cylinder walls and makes the motor run rich all day. One that sticks closed cooks the powerhead in minutes. Either way the rubber ring under the cover is usually hard by the time anyone opens the housing, so it comes in the kit.
Specifications
| Specification | Detail |
|---|---|
| Condition | New / New with tags |
| Type | Outboard thermostat kit |
| Fits | Mercury and Mariner 8 HP to 50 HP four stroke outboards |
| Years | 1995 to 2014 depending on model |
| Opening Temperature | 130 degrees F / 54 degrees C |
| Replaces | 825212, 825212001, 825212T02, 855676003 |
| Contents | Thermostat, rubber ring, gasket |
| Net Weight | 63 g including packaging |
| Pack Size | 150 mm x 100 mm x 30 mm |
| Warranty | 3 year |
OEM Cross Reference
| Component | OEM Part Numbers |
|---|---|
| Thermostat | 825212 |
| Thermostat, alternate | 825212001 |
| Thermostat, alternate | 825212T02 |
| Thermostat kit | 855676003 |
| Thermostat kit, alternate | 855676A1 |
| Sierra cross reference | 18-3642 |
Compatible Engines
| Horsepower | Years | Stroke | Notes |
|---|---|---|---|
| 8 HP | 2001 to 2004 | Four stroke | Mercury and Mariner |
| 9.9 HP | 1999 to 2004 | Four stroke | Mercury and Mariner |
| 15 HP | 1999 to 2006 | Four stroke | Mercury and Mariner |
| 25 HP | 1999 to 2005 | Four stroke | Mercury and Mariner |
| 30 HP | 1999 to 2005 | Four stroke | Mercury and Mariner |
| 40 HP | 1999 to 2014 | Four stroke | Mercury and Mariner |
| 45 HP | 1996 to 2000 | Four stroke | Mercury and Mariner |
| 50 HP | 1995 to 2000 | Four stroke | Mercury and Mariner |
What's Included
| Component | Part Number | Qty |
|---|---|---|
| Thermostat | 825212 | 1 |
| Rubber ring | Included, number not listed | 1 |
| Gasket | 824853, also sold as 27-824853 | 1 |
Cold Motor Or Hot Alarm
| What You See | What It Means | What To Do |
|---|---|---|
| Motor never reaches normal temperature | Thermostat stuck open | New thermostat kit |
| Overheat alarm after a few minutes | Thermostat stuck closed | New thermostat kit, then check the pump |
| Temperature swings at idle | Thermostat opening late | New thermostat kit |
| Water leaking at the thermostat cover | Hard or flattened rubber ring | Kit with the new ring and gasket |
| Plugs sooty and motor rich | Motor running cold | New thermostat, then recheck the plugs |
| Tell tale weak | Water pump, not the thermostat | Check the impeller first |
Fitting Notes
| Step | Action |
|---|---|
| 1 | Confirm the model and year, 8 HP to 50 HP and 1995 to 2014 |
| 2 | Flush the motor and let it cool before opening the housing |
| 3 | Drain the housing and catch the coolant, it comes out hot |
| 4 | Take the cover off and lift the old thermostat and ring out |
| 5 | Clean both faces and check the cover for corrosion |
| 6 | Fit the new thermostat the right way round, spring toward the block |
| 7 | Seat the new rubber ring and gasket, then close the cover evenly |
| 8 | Run on muffs and check the temperature and for leaks at the cover |
Condition & Warranty
| Item | Detail |
|---|---|
| Condition | New / New with tags |
| Warranty | 3 year |
| Packaging | Sealed retail packaging |
Before You Buy
- Fits Mercury and Mariner 8, 9.9, 15, 25, 30, 40, 45 and 50 HP four stroke outboards
- Year ranges differ by horsepower, check the fitment table
- Opens at 130 degrees F, which is 54 degrees C
- Replaces 825212, 825212001, 825212T02 and 855676003
- Crosses to Sierra 18-3642
- Kit includes the thermostat, the rubber ring and the gasket
- 30-Day Easy Returns
- Ships from our warehouse with tracking
Couldn't load pickup availability
Boat Owners' Review
Before You Buy
Frequently Asked Questions
What is your refund policy?
We offer a 14-day hassle-free return on all products. Items must be unused and in original packaging. Every XRmarine part is also covered by our 1-year warranty against manufacturing defects. If something is not right, email us at info@xrmarineparts.com — replacement or full refund, your choice.
See our full Refund Policy for complete details.
How does shipping work?
Free international shipping on every order — no minimums. We operate a global warehouse network with a main distribution centre in Asia (10-20 business days). We also hold stock in regional warehouses across the United States, Germany, the United Kingdom, Australia, and Poland (opening soon) — most orders arrive in 1-3 business days within those countries and in 2-8 business days to nearby regions. Tracking included.
See our full Shipping Policy.
How do you keep prices fair?
We cut out the middlemen. XRmarine sources directly from quality manufacturers and sells at honest prices. Same OEM-quality parts, no dealership markup. Every order comes with free shipping, real expert support, and a 1-year warranty.
Learn more on our About Us page.
What payment methods do you accept?
We currently accept PayPal — a fast, secure way to pay online. Credit card payments (Visa, Mastercard, American Express) and Shopify Payments are being set up and will be available soon. We appreciate your patience.