Knock Sensor – Fits Mercury MerCruiser OMC Volvo Penta 5.0 5.7 (Replaces 806612T, 3850357, R020027, 18-7677)

Product Details

This Knock Sensor is designed for GM small block V8 marine engines, including the 305 (5.0L), 350 (5.7L), and 377 (6.2L) powerplants found in Mercury MerCruiser, OMC, Volvo Penta, PCM, Marine Power, and Crusader applications. The sensor installs into the water port in the middle of the engine block, just above the oil pan, where it monitors combustion events to detect pre-ignition or detonation.

This aftermarket unit replaces Mercury MerCruiser 806612T, OMC/Volvo Penta 3850357, Crusader R020027, and Sierra 18-7677.

• Detects pre-ignition and detonation, signaling the ECM to retard timing and prevent piston or valve damage
• Mounts in the block water port above the oil pan on GM small block engines
• Direct fit for multiple marine brands using GM V8 platforms

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Technical Specs

Engine Type

GM Small Block V8 (305, 350, 377)

Application

Marine (MerCruiser, OMC, Volvo Penta, PCM, Marine Power, Crusader)

Function

Detects pre-ignition/detonation; sends signal to ECM to retard timing

Mounting Location

Water port in engine block, above oil pan

What's in the Box

• 1 × Knock Sensor

Installation Notes

1. Disconnect the battery and ensure the engine is cool before beginning work.
2. Locate the water port on the side of the engine block, just above the oil pan.
3. Disconnect the electrical connector from the old knock sensor.
4. Remove the old sensor using the appropriate socket or wrench.
5. Inspect the mounting threads in the block for damage or debris; clean if necessary.
6. Install the new knock sensor hand-tight, then torque to manufacturer specification (typically 12–18 ft-lbs; consult your engine manual).
7. Reconnect the electrical connector until it clicks into place.
8. Reconnect the battery and start the engine to verify proper operation and absence of fault codes.

Troubleshooting & FAQ

What are the symptoms of a failing knock sensor?

Common signs include engine pinging or knocking under load, reduced power, poor fuel economy, and illuminated check-engine light with knock sensor fault codes. If the ECM cannot detect detonation, it may run overly conservative timing maps or allow damaging knock to occur.

Where exactly does this sensor install?

The knock sensor threads into a water port on the side of the engine block, positioned in the middle of the block just above the oil pan on GM small block V8 engines. This central location allows it to monitor vibrations across all cylinders.

Can I test my old knock sensor before replacing it?

Yes. Use a multimeter to measure resistance across the sensor terminals (typical range 93–107 kΩ at room temperature, but verify your engine's spec). You can also tap the sensor lightly with a small wrench while monitoring voltage output on a scan tool; a healthy sensor will produce a brief voltage spike.

Will this sensor work on freshwater and saltwater engines?

Yes. The sensor is compatible with both freshwater and saltwater marine applications. Ensure all electrical connections are sealed and protected from corrosion, especially in saltwater environments.

What torque specification should I use?

Typical torque is 12–18 ft-lbs, but always consult your engine service manual for the exact value. Over-tightening can damage the sensor or block threads; under-tightening may cause poor thermal contact or leaks.

How often should the knock sensor be replaced?

Knock sensors do not have a fixed service interval and are typically replaced only when they fail or produce fault codes. Regular engine maintenance and using quality fuel can extend sensor life.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 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 issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

• Verify images/specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.