Temperature Sensor for MerCruiser Stern Drives – Replaces 805218T, 805218 and Sierra 18-7600

Product Details

This Temperature Sensor is an aftermarket replacement for applications listed under MerCruiser stern and out-drive systems. It is intended to sense engine temperature and provide the corresponding signal to the boat's temperature gauge or engine monitoring system.

The company catalog lists this sensor for MerCruiser references 805218T and 805218, with additional listed applications and reference numbers for Crusader, OMC Cobra, Volvo Penta, Johnson/Evinrude, Mallory, Sierra, and CDI applications. Always compare the original sensor, connector, thread and application details before ordering.

• Aftermarket replacement temperature sensor
• Listed for MerCruiser stern and out-drive applications
• Reference numbers include MerCruiser 805218T and 805218
• Verify the complete engine and drive application before installation

Part Number Matrix

The following numbers are listed as OEM or aftermarket reference numbers for this sensor. Reference-number listings do not replace confirmation of the complete engine, drive and serial-number application.

Engine & Model Compatibility

Compatibility depends on the exact engine configuration and drive application. Catalog information specifically lists the MerCruiser temperature-sensor application for MCM/MIE 4.3L MPI and 5.0L MPI engines, along with additional MerCruiser MPI applications. The company catalog also identifies MerCruiser stern/out-drive, OMC Cobra stern/out-drive and Volvo Penta stern/out-drive applications.

Technical Specs

Part Type

Temperature Sensor

Product Type

Single aftermarket sensor

Primary Application

MerCruiser stern and out-drive systems

MerCruiser References

805218T, 805218

Additional Listed References

18-7600, 9-42402, R020019, 47002, E13-0009 and 3850397

What's in the Box

• 1 × Temperature Sensor

Installation Notes

1. Disconnect the battery and follow the engine manufacturer's safety procedures before beginning work.
2. Allow the engine and cooling system to cool completely to avoid burns.
3. Locate the existing temperature sensor and compare the replacement with the original part before removal.
4. Disconnect the electrical lead or connector from the original sensor.
5. Use the correct wrench or socket to remove the original sensor without damaging the mounting boss.
6. Apply thread sealant only if required by the engine manufacturer's service information. Do not cover the electrical contact or use a sealant that can affect sensor grounding.
7. Install the replacement sensor and tighten it according to the applicable service-manual specification. Do not guess the torque or thread specification.
8. Reconnect the electrical lead or connector and check that it is secure.
9. Reconnect the battery, start the engine and confirm that the temperature gauge or monitoring system operates normally.

Troubleshooting & FAQ

How do I know if my temperature sensor is failing?

Possible symptoms include erratic temperature readings, a gauge that remains at zero or maximum, or an overheat warning that does not match the actual engine temperature. Check the wiring, connector, cooling system and gauge circuit before replacing the sensor.

Will this sensor fit my MerCruiser 4.3L or 5.0L engine?

The catalog lists the related temperature-sensor application for MCM/MIE 4.3L MPI and 5.0L MPI engines. Verify the exact engine configuration, drive, year or serial-number range and the number on your original sensor before ordering.

Does this sensor fit every MerCruiser 3.0L, 4.3L or 5.0L engine?

No universal fitment should be assumed. The available catalog information does not establish every 3.0L, 4.3L or 5.0L variant. Confirm the engine's exact configuration and compare the original part before purchase.

What thread size does this sensor use?

The available product record does not specify a thread size. Compare the original sensor and consult the applicable engine service manual rather than relying only on a model or reference number.

Do I need thread sealant for installation?

Follow the engine manufacturer's service manual. Some applications require a compatible thread sealant, while others depend on the sensor's sealing or grounding arrangement. Incorrect sealant can affect sensor operation.

Can I test the sensor before installing it?

Testing procedures vary by sensor and engine system. Use the resistance or circuit-testing procedure and temperature values specified in the applicable service manual. Also inspect the wiring, connector and gauge circuit.

Is this an OEM part?

No. This listing is for an aftermarket replacement temperature sensor. The part-number references are provided to help compare the replacement with the original application.

Shipping speed & cost

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If an issue arises, contact support with your order details. Returns are accepted within our standard window when the item is unused and in its original condition. See our policy page or contact support for instructions.

Safety & Important Info

• Confirm the original sensor, connector, thread and application before purchase.
• Keep engine model, drive type, year and serial-number conditions together when checking fitment.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended when the correct application or installation procedure is uncertain.
• Do not operate the engine if the temperature gauge or overheat-warning system is not functioning correctly.

About Sea Sierra

• Marine replacement parts selected for practical service and repair applications.
• Global fulfillment with standard delivery options available to most regions.
• Customer support for product-reference and installation questions.