Thermo Sensor 804295T for Mercury Mariner 75 80 90 100 115 HP 4-Stroke Outboard
Thermo Sensor 804295T for Mercury Mariner 75 80 90 100 115 HP 4-Stroke Outboard
Product Overview
Thermo sensor for the Mercury and Mariner 75, 80, 90, 100 and 115 HP four stroke EFI outboards, the coolant temperature sensor that replaces Mercury 804295T. It fits 8 model groups, and the listing gives serial number ranges rather than years so you can match it to your engine exactly.
The thermo sensor is the one that tells the engine management how hot the coolant is. It sits in the water jacket and its resistance falls as the water heats up, and everything from the enrichment on a cold start to the overheat horn depends on that reading being right.
When one goes, it usually does not stop the engine. It lies: the gauge sits low when the engine is hot, or the overheat warning sounds on a cold engine, or the ECU holds the engine in a cold enrichment it does not need. All three of those cost fuel and none of them look like a sensor fault.
The other way it fails is the opposite one. A sensor reading hot all the time will keep the engine out of its protection, or put it into it, depending on which way it has drifted. On a four stroke outboard that is worth changing before a season rather than after.
This is the sensor on its own. The sealing washer and the connector are not in the pack.
Specifications & Attributes
| Specification | Detail |
|---|---|
| Condition | New / New with tags |
| Type | Thermo sensor, coolant temperature |
| Mercury Number | 804295T |
| Fits | Mercury and Mariner 75, 80, 90, 100 and 115 HP four stroke |
| Engine | Four stroke, EFI |
| Serial Ranges | 8 model groups, listed in the table below |
| Parts In Pack | 1 thermo sensor |
| Quantity | 1 |
| Net Weight | 70 g including packaging |
| Packaging Size | 15 x 10 x 4 cm |
| Packaging | Pack |
| Warranty | 3 year |
OEM Cross Reference
| Brand | Part Numbers |
|---|---|
| Mercury | 804295T |
| Mariner | 804295T |
804295T is the only number given for this sensor across all three of the listings for it. Mercury and Mariner are the same engine under two brands, so the same number covers both.
Compatible Engines
| Model | Serial Range |
|---|---|
| 75 (4-Stroke) | 0G960500 to 0T800999, and 0T801000 to 1B226999 |
| 75 (4-Stroke) Bodensee | 0G960500 to 0T800999, and 0T801000 to 1B226999 |
| 75 EFI (4-Stroke) | 1B172291 to 1B366822 |
| 80 EFI (4-Stroke) | 1B227000 to 1B366822 |
| 90 (4-Stroke) | 0G960500 to 0T800999, and 0T801000 to 1B226999 |
| 90 EFI (4-Stroke) | 1B172291 to 1B366822 |
| 100 EFI (4-Stroke) | 1B227000 to 1B366822 |
| 115 EFI (4-Stroke) | 0T178500 to 0T800999, 0T801000 to 1B226999, and 1B227000 to 1B366822 |
Eight model groups across 75, 80, 90, 100 and 115 HP. The listing gives serial number ranges rather than model years, which is the reliable way to identify a Mercury: find the serial plate on the transom bracket and check it against the range for your model.
The engine type on the listing for this sensor is written as 75HP 80HP 90HP 100HP 115HP outboard, and the model groups in the table above are those same five horsepower ratings split by the serial ranges Mercury gives for each build.
The Bodensee version of the 75 HP is the European emissions version of the same engine, built for the Lake Constance rules. It uses the same sensor as the standard 75 HP, and it is listed separately only because Mercury lists it separately.
Some of the models appear more than once with different serial ranges, because the range was split when the engine changed. If your serial is in any of the ranges against your model, this is the sensor for it.
What's Included
| Component | Detail | Qty |
|---|---|---|
| Thermo sensor | Mercury 804295T | 1 |
One thermo sensor. No sealing washer and no connector are included.
Key Features
| Feature | Detail |
|---|---|
| Direct replacement | Replaces Mercury 804295T |
| 75, 80, 90, 100 and 115 HP | The full four stroke EFI range |
| Serial numbers given | Eight model groups with their ranges |
| Coolant temperature | This is the sensor the gauge and the warning horn read |
| One sensor | Sensor only, no washer |
| Mercury and Mariner | The same engine under both brands |
Signs The Thermo Sensor Has Failed
| What You See | What It Means | Action |
|---|---|---|
| Overheat warning on a cold engine | Sensor reading hot when the engine is cold | Fit a new sensor |
| Gauge stays low with the engine hot | Sensor not reading, no protection | Fit a new sensor before the engine is run hard |
| Gauge moves in steps rather than smoothly | Sensor on its way out | Fit a new sensor |
| Rough running and poor fuel from cold | ECU holding cold enrichment it does not need | Fit a new sensor and check the thermostat |
| Overheat horn never sounds | Sensor dead, the engine has no protection | Fit a new sensor |
Fitting Notes
| Step | Action |
|---|---|
| 1 | Find the serial number on the transom bracket and check it against the table above |
| 2 | Drain the cooling system down below the sensor, or have a plug ready for the hole |
| 3 | Disconnect the battery and unplug the sensor connector |
| 4 | Check the plug and the loom for corrosion before you fit the new one |
| 5 | Undo the sensor and take the old sealing washer out with it |
| 6 | Clean the thread in the housing, do not chase it with a tap |
| 7 | Fit the new sensor with a new sealing washer and torque it to the figure in the manual |
| 8 | Refill and run the engine on muffs, check for leaks at the sensor and watch the gauge |
| 9 | Run it up to temperature and confirm the gauge reads and the warning horn works |
Condition & Warranty
| Item | Detail |
|---|---|
| Condition | New / New with tags |
| Warranty | 3 year |
| Packaging | Pack |
Before You Buy
- Thermo sensor for the Mercury and Mariner 75, 80, 90, 100 and 115 HP four stroke EFI outboards
- Replaces Mercury 804295T
- Fits the 75, 80, 90, 100 and 115 HP four stroke EFI models
- Eight model groups with serial number ranges on the listing
- Includes the Bodensee version of the 75 HP
- One sensor, sealing washer not included
- 70 g with packaging, box 15 cm x 10 cm x 4 cm
- 30-Day Easy Returns
- Free Worldwide Shipping
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