Sierra 18-5898 Temperature Sender, 1/2-14 NPT Thread, Replaces Mercury 97258A1

The Sierra 18-5898 Temperature Sender is a replacement engine temperature sending unit built with a 1/2 inch-14 NPT thread and a 10-32 stud terminal for connecting to the gauge wiring harness. It is designed for a 240 degree Fahrenheit temperature range, matching the sending units used on many Mercury Marine and other marine engine applications. Sierra engineers this sender to meet or exceed the performance of the original equipment part it replaces, giving boat owners a reliable, direct-fit option when the factory sender fails or reads inaccurately.

This sender threads directly into the engine block or manifold temperature port and relays coolant or engine temperature data to the helm gauge, helping monitor engine health and prevent overheating damage. It is cross-referenced to numbers used by Crusader, Mallory, Medallion, Mercruiser, OMC, Stewart Warner, and Veethree Seastar, making it a common replacement across a range of inboard and stern drive engines that use this thread size and terminal configuration.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5898
• Thread Size: 1/2 inch -14 NPT
• Terminal Type: 10-32 stud
• Temperature Range: 240 degrees Fahrenheit
• Weight: 0.15 pounds

Fitment

Fits engines and applications using a 1/2 inch-14 NPT temperature sender port with a 10-32 stud terminal, including engines originally equipped with the cross-referenced OEM senders listed below.

Replaces (OEM)

• Crusader 700427
• Mallory 9-42401
• Medallion A-2618-4
• Mercruiser 34625
• Mercury Marine 97258
• Mercury Marine 97258A1
• FI6900152
• FI6900198
• OMC 171960
• Stewart Warner 362BB-D
• Veethree Seastar 52320S017

Frequently Asked Questions

What thread size does the Sierra 18-5898 temperature sender use? It uses a 1/2 inch-14 NPT thread, which is the same thread size as the original sending unit it is designed to replace.

What temperature range is the 18-5898 sender rated for? The Sierra 18-5898 is designed for a 240 degree Fahrenheit temperature range, matching common marine engine temperature gauge setups.

What kind of terminal connection does this sender have? A 10-32 stud terminal is used on the 18-5898, which connects to the wiring lead running to the temperature gauge at the helm.

Will the Sierra 18-5898 work as a direct replacement for a Mercury 97258A1 sender? Yes, the 18-5898 is cross-referenced to replace Mercury Marine 97258 and 97258A1 temperature senders.

Is the 18-5898 compatible with OMC engines? Yes, this sender is cross-referenced to OMC part number 171960 for both inboard and stern drive applications.

Does the Sierra 18-5898 replace Crusader or Mallory senders? Yes, it cross-references to Crusader 700427 and Mallory 9-42401, along with several other OEM equivalents.

How much does the 18-5898 temperature sender weigh? The Sierra 18-5898 weighs 0.15 pounds.

Is the Sierra 18-5898 an OEM or aftermarket part? It is an aftermarket Sierra replacement sender engineered to meet or exceed the performance of the original equipment part it replaces.

What is included when I order the 18-5898? The order includes one Sierra 18-5898 temperature sending unit with its 10-32 stud terminal.

Does this sender fit Stewart Warner and Veethree Seastar gauge systems? Yes, the 18-5898 cross-references to Stewart Warner 362BB-D and Veethree Seastar 52320S017 sending units.

What does a temperature sender like the 18-5898 do? It threads into the engine and sends a temperature signal to the helm gauge, allowing the operator to monitor engine temperature and catch overheating before it causes damage.