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

$39.00

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You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This is a direct-replacement Bi-Directional Water Pump – Fits Volvo Penta & MerCruiser 4.3L-6.3L Inboard Engines. It is designed for reliable, efficient cooling in Volvo Penta 4.3L, 5.0L, 5.7L, 6.2L, and 6.3L inboard engines, as well as MerCruiser 4.3L, 5.0L, 5.7L, 6.2L, and 6.3L sterndrive and inboard motors. Constructed from durable cast iron with brass fittings and a stainless steel backing plate, it offers superior corrosion resistance in marine environments.

This pump serves as a direct interchange for MerCruiser part numbers 46-8M0113734, 8503991, and 850399002; Volvo Penta 3853850; Crusader RA057018; and Sierra 18-3599-1/18-3599-2.

Engineered for straightforward, direct-mount installation on the engine block.
Compatible with both steel and composite timing chain covers.
Includes a new gasket set for a complete and secure installation.

Part Number Matrix

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

Brand	Part Number
MerCruiser	46-8M0113734
MerCruiser	8503991
MerCruiser	850399002
MerCruiser	878341
MerCruiser	811841
MerCruiser	60658
MerCruiser	17437
Volvo Penta	3853850
Crusader	RA057018
Sierra	18-3599-1
Sierra	18-3599-2

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For MerCruiser sterndrive and inboard motors, this pump is compatible with both steel and composite timing chain covers across all listed small block V8 engines.

Brand	Model	Rated HP	OEM Part No.	Notes
MerCruiser	4.3L Sterndrive	4.3L V6	46-8M0113734, 8503991, 17477, 850399002	Compatible with steel and composite timing chain covers
MerCruiser	5.0L Sterndrive	5.0L V8	46-8M0113734, 8503991, 17477, 850399002
MerCruiser	5.7L Sterndrive	5.7L V8	46-8M0113734, 8503991, 17477, 850399002
MerCruiser	6.2L Sterndrive	6.2L V8	46-8M0113734, 8503991, 17477, 850399002
MerCruiser	6.3L Sterndrive	6.3L V8	46-8M0113734, 8503991, 17477, 850399002

For Volvo Penta inboard engines, this pump is typically located above the lower gear case assembly.

Brand	Model	Rated HP	OEM Part No.	Notes
Volvo Penta	4.3L Inboard	4.3L V6	3853850	Located above the lower gear case assembly
Volvo Penta	5.0L Inboard	5.0L V8	3853850
Volvo Penta	5.7L Inboard	5.7L V8	3853850
Volvo Penta	6.2L Inboard	6.2L V8	3853850
Volvo Penta	6.3L Inboard	6.3L V8	3853850

Technical Specs

Product Type: Bi-directional water circulation pump
Installation: Direct replacement, straightforward installation
Connection: Direct mount to engine block
Housing Material: Cast iron with brass fittings
Housing Color: Black
Fitting Type: Brass bi-directional impeller
Warranty: Lifetime warranty (via AA Ignition)
Other Technical Attributes: Stainless steel backing plate for corrosion resistance

What’s in the Box

1 x Bi-directional Water Pump
1 x Gasket set (18-0891)

Installation Notes

Disconnect the battery and drain the cooling system completely.
Loosen the serpentine belt and remove it from the water pump pulley.
Remove the pulley bolts and the pulley itself.
Disconnect the hoses attached to the water pump. Be prepared for some residual coolant spillage.
Unbolt the old water pump from the engine block and carefully remove it.
Clean the mounting surface on the engine block, removing all old gasket material and residue.
Place the new gasket on the engine block, aligning it with the bolt holes.
Mount the new water pump, ensuring it is properly seated against the gasket. Hand-tighten the bolts initially.
Torque the mounting bolts to the manufacturer's specified value and sequence.
Reinstall the pulley, hoses, and serpentine belt.
Refill the cooling system with the appropriate coolant.
Reconnect the battery, start the engine, and check for leaks and proper operation.

Troubleshooting & FAQ

How do I know if my water pump is failing?

Common signs of a failing water pump include coolant leaks from the pump itself, engine overheating, a whining or grinding noise from the engine bay, or a loose or wobbly water pump pulley.

Is this pump uni-directional or bi-directional?

This is a bi-directional pump, meaning it is designed to circulate coolant effectively regardless of the engine's rotation direction. This makes it versatile for a wide range of compatible MerCruiser and Volvo Penta engines.

Will this fit an automotive engine?

No, this water pump is specifically designed for marine applications. It uses materials like a cast iron housing, brass impeller, and stainless steel backing plate to resist corrosion from saltwater and freshwater environments, which are not standard in automotive pumps.

What is the difference between pumps for steel vs. composite timing covers?

This specific pump model is confirmed to be compatible with both steel and composite timing chain covers on all compatible small block V8 engines, simplifying the selection process.

Does this pump include a new gasket?

Yes, a new gasket set (part number 18-0891) is included in the box to ensure a proper seal during installation.

What is the recommended replacement interval?

While there is no fixed interval, marine water pumps are critical wear items. It is recommended to inspect them annually for leaks, bearing play, or corrosion and replace them as part of preventative maintenance every few hundred hours or every 3-5 years, depending on usage and water conditions.

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 vs 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.

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