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Water Temp Sender 12415 – 1/8"-27 NPT Fits Mercury 40–200HP
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How to Match This Part
This aftermarket water temperature gauge sender replaces Mercury / Quicksilver 12415. It threads into a 1/8"-27 NPT cooling-passage port and sends a resistance signal to a single-station analog water temperature gauge. The stud terminal carries the gauge signal; the brass body grounds through the engine casting.
Match this part in this order:
1. OEM number on the removed sender or in your parts catalog (Mercury 12415, or Sierra 18-5896)
2. Port thread and gauge type — port must be 1/8"-27 NPT; gauge must be a resistance-type analog water temperature gauge
3. Engine model / HP on the Mercury or Mariner identification plate, then compare form to the product images
Identify the form from the product images: brass-colored hex body for wrench grip, tapered male pipe thread, short sensing probe below the threads, and a single top stud terminal with nut and washer. If your original unit has two terminals, a different thread, or a switch-style spade connector, it is not this part.
Part Number Cross-Reference
Use this table to confirm equivalent part numbers across OEM and aftermarket brands.
| Type | Brand | Part Number | Notes |
|---|---|---|---|
| OEM | Mercury / Mariner / Quicksilver | 12415 | Primary original equipment temperature sender |
| Aftermarket | Sierra | 18-5896 | Direct replacement, single station |
Part numbers are listed for identification only. This is an aftermarket part manufactured by JLM Marine and is not sold as a genuine Mercury component.
Compatible Engine Models
Confirm your engine model and serial number before ordering. For Mercury and Mariner outboards, the serial number is on the mounting bracket or cowl identification plate. Cross-check with the Mercury Serial Number Guide and Mercury Parts Diagrams. This sender requires an open 1/8"-27 NPT cooling port and a resistance-type analog water temperature gauge.
| Brand | Application | HP Coverage | Notes |
|---|---|---|---|
| Mercury / Mariner | Outboard engines calling for sender 12415 | 40–200 HP | Confirm 1/8"-27 NPT port and OEM 12415 on the removed sender |
Technical Specifications
| Specification | Value |
|---|---|
| Primary OEM | 12415 |
| Product type | Engine water temperature gauge sender |
| Thread size | 1/8 in. – 27 NPT |
| Terminal | 10-32 threaded stud (single terminal) |
| Gauge stations | Single station |
| Gauge scale compatibility | US ohm-scale marine temperature gauges |
| Application | Mercury / Mariner outboard cooling temperature signal to dash gauge |
Installation Guide
1
Allow the engine to cool fully and disconnect the battery negative cable before opening the sender port.
2
Label and remove the gauge wire from the old sender stud. Unscrew the old sender and confirm it is 1/8"-27 NPT. Clean the port threads to bright metal so the new body can ground correctly.
3
Apply a thin coat of non-hardening marine thread sealant suitable for NPT fittings. Avoid heavy PTFE tape wraps that can block the ground path through the sender body. Thread the sender in by hand, then snug with a wrench — do not over-torque this small fitting.
4
Reconnect the gauge wire under the 10-32 stud nut with a marine-grade ring terminal. Reconnect the battery, run the engine on a flush kit or in the water, and confirm the gauge needle climbs smoothly as temperature rises.
Note: Professional installation is recommended when you are unsure about sender location, grounding, or gauge wiring.
Troubleshooting & FAQ
Important Notes
- This is a gauge sender, not an overheat warning switch. Do not substitute it for a switch-style temperature sensor.
- The sender body must ground through the engine casting — do not isolate the threads with heavy PTFE tape wraps.
- Verify the removed sender is OEM 12415 (or Sierra 18-5896) and that the port is 1/8"-27 NPT before installing.
Why Choose JLM MARINE?
- Quality Control: Each batch is inspected for dimensional consistency and workmanship before shipment.
- Support: Marine parts specialists can help you confirm OEM number, thread size, and gauge type before you order.
We can ship to virtually any address in the world with free shipping available for most regions.
For our typical US and Canadian customers , our shipping timeframes are as follows:
- Amazon FBA: orders will be delivered within 1-5 business days after placing the order (during certain special periods such as major promotions, Christmas, etc., the delivery time of Amazon FBA may be affected).
- US warehouse shipment: orders will be delivered within 5 days after placing the order.
- China warehouse shipment: orders will be delivered about 12 days after placing the order.
When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.
Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.
Founded in 2002, JLM Marine has established itself as a dedicated manufacturer of high-quality marine parts, based in China. Our commitment to excellence in manufacturing has earned us the trust of top marine brands globally.
As a direct supplier, we bypass intermediaries, which allows us to offer competitive prices without compromising on quality. This approach not only supports cost-efficiency but also ensures that our customers receive the best value directly from the source.
We are excited to expand our reach through retail channels, bringing our expertise and commitment to quality directly to boat owners and enthusiasts worldwide.
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