806490T Temperature Sending Unit Sensor for Mercury Mercruiser OMC Volvo Penta | JLM Marine

Temperature Sending Unit Sensor – Fits Mercury Mercruiser, OMC, Volvo Penta & More

This high-quality aftermarket temperature sending unit sensor is designed to fit a wide range of marine engines including Mercury Mercruiser, OMC, Volvo Penta, PCM, Indmar, and other compatible inboard/sterndrive applications. Featuring a standard 3/8-18 NPT thread, this sensor ensures accurate temperature monitoring for reliable engine performance.

Direct Replacements: Mercury Mercruiser 806490T | OMC/Volvo Penta 3853787 | Sierra 18-5897 | Mallory 9-42400

• Standard 3/8-18 NPT thread for universal fitment
• Compatible with multiple marine engine brands
• Drop-in replacement for OEM temperature sensors

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

This temperature sending unit sensor is compatible with Mercury Mercruiser, OMC, Volvo Penta, PCM, Indmar, and other marine engines equipped with a 3/8-18 NPT temperature sensor port. Please verify your original sensor's thread size and terminal configuration before ordering.

Technical Specifications

Package Contents

• 1 × Temperature Sending Unit Sensor (806490T)

Installation Guide

1. Disconnect the battery to prevent electrical shorts during installation.
2. Locate the existing temperature sensor on your engine block or cylinder head. It typically has a single wire connector.
3. Disconnect the wire terminal from the old sensor by carefully pulling it straight off.
4. Using an appropriate wrench, unscrew the old temperature sensor counterclockwise. Be prepared for minor coolant drips.
5. Clean the threads in the engine block port to remove any old sealant or debris.
6. Apply a small amount of thread sealant (Teflon tape or pipe sealant rated for coolant) to the new sensor's threads.
7. Hand-thread the new sensor clockwise into the port until snug, then tighten with a wrench. Do not over-torque.
8. Reconnect the wire terminal firmly onto the new sensor's spade connector.
9. Check coolant level and top off if necessary after installation.
10. Reconnect the battery and start the engine to verify proper gauge operation.
11. Monitor for leaks around the sensor during the first few minutes of operation.
12. Test the temperature gauge to ensure it reads correctly as the engine warms up.

Troubleshooting & FAQ

Q: How do I confirm this sensor fits my engine?
A: Verify that your original sensor has a 3/8-18 NPT thread and a single spade terminal. Cross-reference your current part number with the replacements listed (806490T, 3853787, 18-5897, 9-42400) to ensure compatibility.

Q: What are the signs that my temperature sensor is failing?
A: Common symptoms include erratic temperature gauge readings, a gauge stuck at cold or hot, warning alarms activating randomly, or the gauge not responding at all when the engine is warm.

Q: How often should I replace the temperature sending unit?
A: Temperature sensors don't have a fixed replacement interval but should be inspected during routine maintenance. Replace immediately if you notice inaccurate readings, corrosion on terminals, or coolant leaks around the sensor body.

Q: Can I install this sensor without draining the coolant?
A: Yes, in most cases. The sensor port is usually above the waterline or drains minimally. Have the replacement sensor ready and work quickly—thread it in immediately after removing the old one to minimize coolant loss.

Q: Will this aftermarket sensor read the same as my original OEM sensor?
A: Yes, this sensor is manufactured to OEM specifications with the same resistance curve, ensuring accurate temperature readings identical to the original factory part.

Q: Is this an OEM or aftermarket part?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.