Bi-Directional Water Pump – Fits MerCruiser, Volvo Penta 140-260HP (Replaces 8503991, 8M0113734, 3853850)
Bi-Directional Water Pump – Fits MerCruiser, Volvo Penta 140-260HP (Replaces 8503991, 8M0113734, 3853850) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Bi-Directional Water Pump – Fits MerCruiser, Volvo Penta 140-260HP ...
Bi-Directional Water Pump – Fits MerCruiser, Volvo Penta 140-260HP (Replaces 8503991, 8M0113734, 3853850) is backordered and will ship as soon as it is back in stock.
Product Details
This engine-mounted Bi-Directional Water Pump is designed for a wide range of MerCruiser, Volvo Penta, and OMC V6/V8 marine engines produced between 1963 and 2014. It ensures proper coolant circulation for 4-stroke models, including MerCruiser 140–260 HP engines and Volvo Penta GM 4.3L–6.3L engines.
It serves as a direct replacement or interchange for MerCruiser parts 8503991 and 8M0113734, Volvo Penta 3853850, Sierra 18-3599-1, Crusader 20318, and others.
- Installs directly to the engine block.
- Constructed from cast steel with a stainless steel backing plate for durability.
- Bi-directional flow allows compatibility with steel and composite timing chain covers.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| MerCruiser | 8503991 |
| MerCruiser | 8M0113734 |
| Volvo Penta | 3853850 |
| Sierra | 18-3599-1 |
| Sierra | 18-3599-2 |
| Crusader | 20318 |
| Crusader | 7142520 |
| Pleasurecraft | RA057018 |
Engine & Model Compatibility
Confirm your engine model and year in the table below.
For MerCruiser Owners: This pump fits most V6 and small block V8 engines from 1963–2014, but note the specific exclusion for 4.3L V6 engines from 2007 onwards that lack a water bypass hole.
For Volvo Penta Owners: Broad compatibility with GM-based 4.3L V6 through 6.3L V8 engines from 1973 and later.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 4.3L V6 | 140–200 | 4-Stroke | 1963–2007 | 8503991/8M0113734 | Will NOT fit 2007+ V6 4.3L engines without water bypass hole |
| MerCruiser | 5.0L V8 | 155–205 | 4-Stroke | 1963–2014 | 8503991/8M0113734 | Small block applications |
| MerCruiser | 5.7L V8 | 230–260 | 4-Stroke | 1963–2014 | 8503991/8M0113734 | Small block applications |
| Volvo Penta | GM 4.3L | - | 4-Stroke | 1973 and later | 3853850 | V6 engine |
| Volvo Penta | GM 5.0L | - | 4-Stroke | 1973 and later | 3853850 | Small block V8 |
| Volvo Penta | GM 5.7L | - | 4-Stroke | 1973 and later | 3853850 | Small block V8 |
| Volvo Penta | GM 6.2L | - | 4-Stroke | 1973 and later | 3853850 | Small block V8 |
| Volvo Penta | GM 6.3L | - | 4-Stroke | 1973 and later | 3853850 | Small block V8 |
| OMC | V6/V8 Small Block | - | 4-Stroke | 1968–1998 | - | Small block applications |
| Crusader | Small Block V6/V8 | - | 4-Stroke | - | 20318, 7142520 | Small block applications |
| Indmar | Small Block V6/V8 | - | 4-Stroke | - | - | Small block applications |
| Pleasurecraft | Small Block V6/V8 | - | 4-Stroke | - | RA057018 | Small block applications |
Technical Specs
- Product Type
- Bi-Directional Water Circulating Pump
- Installation
- Engine mounted
- Connection
- Threaded ports with brass fittings
- Housing Material
- Cast steel with stainless steel backing plate
- Housing Color
- Black
- Weight
- 4.55 kg (10.01 lbs)
- Fitting Type
- Brass fittings with hose connections
- Other Technical Attributes
- Bi-directional flow, compatible with steel and composite timing chain covers
- Warranty
- Varies by manufacturer
What’s in the Box
- 1 x Water Circulation Pump (8503991/8M0113734)
Installation Notes
- Disconnect the battery and allow the engine to cool completely.
- Drain the engine coolant into a suitable container.
- Loosen the drive belt and remove hoses connected to the water pump.
- Unbolt and carefully remove the old water pump from the engine block.
- Thoroughly clean the mounting surface on the engine, removing all old gasket material and sealant.
- Install the new water pump with a new gasket (not included), torquing bolts to manufacturer specifications.
- Reconnect hoses and reinstall the drive belt, adjusting it to the proper tension.
- Refill the cooling system with the recommended coolant mixture.
- Reconnect the battery, start the engine, and carefully check for any leaks around the pump and hose connections.
Troubleshooting & FAQ
Will this pump fit a 2008 MerCruiser 4.3L V6?
No, this part is not compatible with MerCruiser 4.3L V6 engines made from 2007 onwards unless the engine block has a water bypass hole. Please verify your specific engine configuration before ordering.
How can I tell if my water pump is failing?
Common signs of a failing water pump include the engine overheating at idle or low speeds, visible coolant leaks from the pump body (often from a "weep hole"), or a grinding/whining noise from the pump pulley area.
Is this pump bi-directional?
Yes, this is a bi-directional pump. It is designed to work with engines that have either standard or reverse rotation water pump systems and is compatible with both steel and composite timing chain covers.
What does a "small block" engine refer to?
"Small block" refers to a specific family of V-style engines, primarily V8s (and related V6s), made by General Motors (GM). This pump is designed for these common marine engine architectures used by MerCruiser, Volvo Penta, OMC, and others.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility and batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit is 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 and 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.
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