Water Temp Alarm Switch 48952 – Fits MerCruiser 3.0–7.4L

How to Match This Part

This aftermarket water temperature alarm switch replaces MerCruiser / Mercury 48952 and supersedes the earlier number 87-806951 / 806951. It is a threaded switch for MerCruiser sterndrive and inboard engines equipped with a factory audio warning system. It closes the warning circuit when coolant temperature rises past the safe range — it is not a dashboard temperature-gauge sender.

Match this part in this order:
1. OEM number on the removed switch or in your parts catalog — 48952, or superseded 87-806951 / 806951
2. Engine model and year — MerCruiser 3.0L, 4.3L, 5.0L, 5.7L, or 7.4L applications that use an audio warning temperature switch (see table below)
3. Physical form — 3/8 in. pipe-thread switch body with a single stud terminal for the warning-system lead (compare with the product images)

Do not use this listing to replace a gauge temperature sender (different function and often a different OEM number). If your engine has no audio warning system, or the removed part number does not match 48952 / 87-806951, choose a different listing.

• Primary OEM: 48952
• Type: Water temperature alarm switch
• Thread: 3/8 in. pipe thread

Part Number Cross-Reference

Use these MerCruiser / Mercury references to confirm interchange. 87-806951 / 806951 is superseded by 48952.

Compatible Engine Models

Confirm your MerCruiser model and year against the table, then verify that the removed part is marked 48952 or 87-806951 / 806951 and that the engine uses an audio warning system. The engine identification plate is typically on the engine block or near the flame-arrestor cover. Parts diagrams: Mercury Parts Diagrams.

Technical Specifications

Installation Guide

1. Allow the engine to cool completely. Disconnect the battery and isolate the audio-warning circuit before opening the cooling system.
2. Locate the original temperature switch at the thermostat housing or cooling-passage port. Note lead routing and terminal orientation.
3. Disconnect the warning lead, then unscrew the switch. Catch residual coolant and keep the port clean.
4. Compare the replacement to the original: 3/8 in. pipe thread, stud terminal, and OEM number 48952 or superseded 87-806951 / 806951.
5. Install with the sealing method and torque called for in your MerCruiser service manual. Reconnect the stud terminal securely.
6. Refill / bleed coolant as required, reconnect the battery, run the engine, and check for leaks plus correct audio-warning operation.

Do not relocate the switch from the factory port. Nuts, lock washers, sealant, and coolant are not included with this listing unless shown in your product images.

Troubleshooting & FAQ

Is this a gauge temperature sender?
No. This is an audio-warning temperature switch for the alarm/buzzer circuit. Gauge senders use different OEM numbers and drive the dash temperature gauge.

My old part is stamped 87-806951 or 806951 — will 48952 work?
Yes. 87-806951 / 806951 is superseded by 48952. Confirm thread and stud form against the removed part and the product images.

Does every MerCruiser 5.7L use this switch?
No. Coverage here is for engines that call for OEM 48952 (or superseded 87-806951) and are equipped with an audio warning system within the year bands listed above.

Is this a genuine Mercury / MerCruiser part?
No. This is an aftermarket replacement manufactured to match the OEM-reference fit and function. It is not a Mercury Marine or MerCruiser genuine part.

Why Choose JLM MARINE?

• Precision Fit: Form and thread intended for MerCruiser 48952 audio-warning temperature switch applications on the listed sterndrive and inboard engines.
• Quality Control: Each batch is inspected for dimensional consistency and workmanship.
• Direct from Manufacturer: Aftermarket marine sensors and switches engineered as direct replacements — not remanufactured cores.