Temperature Sender 12415 for Mercury Mariner 1/8 in NPT 240 F 18-5896
Temperature Sender 12415 for Mercury Mariner 1/8 in NPT 240 F 18-5896
Product Overview
Temperature sender for Mercury and Mariner outboards, the sensor part that screws into the block or the cylinder head and drives the dash gauge. It replaces Mercury 12415 and crosses to Sierra 18-5896, it has a 1/8 inch 27 NPT thread and a 240 °F gauge range, and one sender ships in a 155 mm x 100 mm x 50 mm box at 76 g.
The sender is a resistance element that changes with temperature, so the gauge reads a scale rather than a switch. That is why the thread size and the gauge range both have to match: a sender with the wrong range reads hot or cold across the whole dial even though it is working.
These are also sold as universal senders for oil or water. The body will go into any 1/8 inch NPT port, but the reading a boat owner cares about is the one on their own gauge face, so match the range to the gauge before buying.
A sender fails in two ways. Either it drifts and the gauge sits higher or lower than it used to, or it goes open circuit and the gauge drops to the bottom stop or pegs hot as soon as the ignition is switched on. A quick check is to earth the sender wire: if the gauge swings to full scale, the sender is at fault rather than the gauge or the wiring.
Fitment is by part number on this one, because Mercury lists 12415 against a range of models rather than a single family. Check the number on the old sender and the thread in the port before ordering.
Specifications & Attributes
| Specification | Detail |
|---|---|
| Condition | New / New with tags |
| Type | Temperature sender |
| Mercury Part Number | 12415 |
| Sierra Number | 18-5896 |
| Thread Size | 1/8 inch 27 NPT |
| Range | 240 °F |
| Application | Water or oil temperature gauge sender |
| Fits | Mercury and Mariner outboards that use 12415 |
| Country of Origin | Taiwan |
| Quantity | 1 sender |
| Net Weight | 76 g including packaging |
| Packaging | 155 mm x 100 mm x 50 mm |
| Packaging In Inches | 6.10 in x 3.94 in x 1.97 in |
| Warranty | 3 year |
OEM Cross Reference
| Brand | Part Numbers |
|---|---|
| Mercury | 12415 |
| Mercury / Mariner | 12415 |
| Sierra | 18-5896 |
Compatible Engines
| Brand | Application | Note |
|---|---|---|
| Mercury / Mariner | Models that use sender 12415 | Not listed by the maker, check the part number |
| Mercury / Mariner | Dash water or oil temperature gauge | 240 °F scale |
What's Included
| Component | Detail | Qty |
|---|---|---|
| Temperature sender | 1/8 inch 27 NPT, 240 °F range | 1 |
| Sealing washer | Not included, fit a new one if the old one is crushed | 0 |
| Terminal nut | Not included, reuse the original if it is sound | 0 |
When A Sender Needs Replacing
| What You See | What It Means | Action |
|---|---|---|
| Gauge pegs hot as soon as the ignition is on | Sender shorted or wire earthed | Check the wire, then fit a new sender |
| Gauge stays at the bottom stop | Sender open circuit | Fit a new sender |
| Gauge reads lower than it used to | Element drifting with age | Fit a new sender |
| Gauge reads high but the engine is not hot | Sender range does not match the gauge | Fit the correct sender |
| Reading jumps around | Loose terminal or corroded thread | Clean the thread and the terminal first |
| Gauge reads correctly on a known good sender | Original sender at fault | Fit a new sender |
Fitting Notes
| Step | Action |
|---|---|
| 1 | Check the part number on the old sender and the thread in the port |
| 2 | Let the engine cool and drain the coolant below the sender if needed |
| 3 | Disconnect the sender wire and check the terminal for corrosion |
| 4 | Take the old sender out and clean the thread in the port |
| 5 | Fit the new sender with a sealing washer and do not overtighten it |
| 6 | Reconnect the wire and refill the coolant |
| 7 | Run the engine and check the gauge climbs slowly as it warms |
| 8 | Earth the sender wire with the ignition on to check the gauge still swings |
Condition & Warranty
| Item | Detail |
|---|---|
| Condition | New / New with tags |
| Warranty | 3 year |
| Packaging | Box, 155 mm x 100 mm x 50 mm |
Before You Buy
- Replaces Mercury 12415 and crosses to Sierra 18-5896
- 1/8 inch 27 NPT thread, the same as the port on the block or head
- 240 °F gauge range, matching the gauge face
- 1/8 NPT is not the same as the 1/2 inch NPT sender used on some V6 and V8 blocks
- Fitment is by part number, Mercury does not list 12415 by model
- One sender, sealing washer not included
- 76 g with packaging, box 155 mm x 100 mm x 50 mm
- 30-Day Easy Returns
- Free Worldwide Shipping
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Boat Owners' Review
Before You Buy
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