Sierra Temperature Sender 18-5896, Replaces Mercury Marine 12415, 1/8"-27 NPT, Fits Mercury Outboards

The Sierra 18-5896 is a temperature sender built for Mercury outboard cooling systems, designed to send water/head temperature readings to a compatible gauge. It threads directly into the cooling passage using a 1/8" - 27 NPT fitting and connects to the gauge circuit through a 10-32 stud terminal. This sender uses a "D" sender code and reads across a 240 degree Fahrenheit range, matching it to gauges calibrated for that sender type. The housing is machined for a precise thread fit and consistent sealing at the mounting point. It is a direct replacement for the original Mercury Marine 12415 sender, so it installs in the factory location without modification on the outboard models it fits. Because sender code and range must match the gauge for accurate readings, this is the correct replacement when the original Mercury 12415 sender has failed or is reading incorrectly. The compact 0.39 x 0.39 x 0.39 inch body keeps it a simple, low-profile threaded-in component rather than a bulky assembly, and its light 0.04 pound weight reflects its small, single-piece construction.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5896
• Sender Code: D
• Temperature Range: 240 degrees Fahrenheit
• Terminal Type: 10-32 stud
• Thread Size: 1/8" - 27 NPT
• Finish: Machined
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• Weight: 0.04 pounds
• UPC: 030999563873
• Replaces: 12415

Fitment

• Mercury 6, 8, 9.9 HP (2 cylinder) outboards, serial number A197112 and later
• Mercury Sea Pro 10 HP outboards, serial number D038000 and later
• Mercury 15 HP (2 cylinder) outboards, serial number B292414 and later
• Mercury 18XD, 20XD, 25XD outboards, serial number B114231 and later

Replaces (OEM)

• 12415

Frequently Asked Questions

What does the Sierra 18-5896 temperature sender do? It measures water or head temperature in a Mercury outboard's cooling system and sends that reading to a compatible temperature gauge, using a sender code D and a 240 degree Fahrenheit range.

Is the Sierra 18-5896 a direct replacement for the Mercury 12415 sender? Yes, the 18-5896 replaces Mercury Marine part number 12415 and installs in the same factory location without modification.

What thread size does the 18-5896 sender use? It has a 1/8" - 27 NPT thread, which screws directly into the outboard's cooling passage.

What terminal connection does this sender use? The Sierra 18-5896 connects to the gauge wiring through a 10-32 stud terminal.

Which Mercury outboards fit the 18-5896 temperature sender? It fits Mercury 6, 8, and 9.9 HP (2 cylinder) outboards from serial number A197112 and later, Mercury Sea Pro 10 HP from serial number D038000 and later, Mercury 15 HP (2 cylinder) from serial number B292414 and later, and Mercury 18XD, 20XD, and 25XD models from serial number B114231 and later.

How do I know if my outboard's serial number qualifies for this sender? Check your outboard's serial number tag against the ranges listed for the 18-5896: for example, 15 HP (2 cylinder) models need serial number B292414 or later to be compatible.

What size is the Sierra 18-5896 sender? It measures 0.39 x 0.39 x 0.39 inches and weighs 0.04 pounds, a small threaded-in component.

What sender code and temperature range does the 18-5896 use? This sender uses sender code D with a 240 degree Fahrenheit range, so it should be paired with a gauge calibrated for that same code and range.

Is the 18-5896 sender made by Sierra genuine, not a generic part? Yes, this is a genuine Sierra part, number 18-5896, manufactured as a direct-fit replacement for the Mercury 12415 sender.

What is the housing finish on the Sierra 18-5896? The 18-5896 has a machined housing for a precise thread fit at the 1/8" - 27 NPT mounting point.

Will the 18-5896 fix an inaccurate temperature gauge reading? If the original Mercury 12415 sender has failed or is sending an incorrect signal, replacing it with the Sierra 18-5896 restores accurate readings to a gauge matched to sender code D and a 240 degree range.