Bi-Directional Water Pump – Fits Volvo Penta & MerCruiser 4.3L-6.3L Inboard Engines

Bi-Directional Water Pump – Fits Volvo Penta & MerCruiser 4.3L-6.3L Inboard Engines (Replaces 850399002, 3853850)

This bi-directional water pump is a direct replacement for circulation pumps on a wide range of Volvo Penta and MerCruiser inboard and sterndrive engines, including 4.3L, 5.0L, 5.7L, 6.2L, and 6.3L models. It is engineered to meet or exceed original equipment specifications for reliable cooling performance.

This part directly replaces MerCruiser part numbers 46-8M0113734, 8503991, 850399002, 878341, 811841, 60658, and 17437, as well as Volvo Penta 3853850, Crusader RA057018, and Sierra 18-3599-1/18-3599-2.

• Installation: Mounts directly to the engine block for a straightforward installation.
• Construction: Features a durable cast iron housing, a corrosion-resistant stainless steel backing plate, and a brass bi-directional impeller.
• Compatibility: Designed for use with both steel and composite timing chain covers on all compatible V6 and small block V8 engines.

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.

Technical Specifications

Package Contents

• 1 x Bi-directional Water Pump (850399002, 3853850)
• 1 x Gasket set (18-0891)

Installation Guide

Follow these general steps for installation. Refer to your engine's service manual for detailed instructions and torque specifications.

1. Disconnect the boat's battery and drain the raw water cooling system.
2. Loosen the alternator and remove the serpentine belt from the circulation pump pulley.
3. Remove the bolts securing the pulley to the pump flange and remove the pulley.
4. Unscrew the mounting bolts holding the water pump to the engine block. Note the location of any hoses connected to the pump.
5. Carefully detach the pump from the engine. Coolant may spill, so have rags ready.
6. Thoroughly clean the gasket mating surface on the engine block, ensuring it is free of old gasket material and debris.
7. Place the new gasket on the engine block, aligning it with the bolt holes.
8. Mount the new water pump, ensuring it sits flush against the gasket, and tighten the mounting bolts to the manufacturer's specified torque.
9. Re-attach the pulley and serpentine belt, adjusting the belt tension as required.
10. Reconnect all hoses, refill the cooling system, reconnect the battery, and start the engine to check for proper operation and leaks.

Troubleshooting & FAQ

How do I confirm this pump fits my MerCruiser or Volvo Penta engine?
This pump is designed for specific 4.3L, 5.0L, 5.7L, 6.2L, and 6.3L inboard and sterndrive engines. Please check the "Compatible Engine Models" table and cross-reference your engine's OEM part number with our list to ensure an exact match.

What are the signs of a failing water pump?
Common signs include engine overheating, coolant leaks from the pump itself (often from the weep hole), a loose or noisy pulley, or steam coming from the engine compartment.

What makes this pump "bi-directional"?
The impeller is designed to circulate coolant effectively regardless of the engine's rotational direction, making it compatible with a wide range of standard and counter-rotating marine engines from Volvo Penta and MerCruiser.

What is this pump made of?
This pump features a robust cast iron housing with durable brass fittings and a stainless steel backing plate for superior corrosion resistance in challenging marine environments.

OEM vs. Aftermarket?
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.

How fast do you ship and how much does it cost?
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.

What is your warranty and return policy?
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.