SKU: 53102274791

Bi-Directional Water Pump for MerCruiser Sterndrive 8503991

$64.79 $71.99
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Description

Bi-Directional Water Pump for MerCruiser Sterndrive 8503991Bi Directional Water Pump Fits MerCruiser V6 V8 Small Block (Replaces 8503991) This engine mounted, bi directional water circulating pump is designed for a wide range of marine engines, including MerCruiser, Volvo Penta, OMC, and other brands using GM small block V6 and V8 engines. It ensures reliable coolant circulation for optimal engine temperature. This component is a direct replacement for MerCruiser part numbers 8503991 and 8M0113734, Volvo

Bi-Directional Water Pump – Fits MerCruiser V6/V8 Small Block (Replaces 8503991)

This engine-mounted, bi-directional water circulating pump is designed for a wide range of marine engines, including MerCruiser, Volvo Penta, OMC, and other brands using GM small block V6 and V8 engines. It ensures reliable coolant circulation for optimal engine temperature.

This component is a direct replacement for MerCruiser part numbers 8503991 and 8M0113734, Volvo Penta 3853850, Sierra 18-3599-1, and others, offering a precise fit for compatible models.

  • Installation: Engine mounted for secure, direct integration.
  • Material: Features a durable cast steel housing with a stainless steel backing plate for corrosion resistance.
  • Compatibility: Designed for both steel and composite timing chain covers.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Brand Part Number
MerCruiser 8503991 / 8M0113734
Volvo Penta 3853850
Sierra 18-3599-1 / 18-3599-2
Crusader 20318 / 7142520
Pleasurecraft RA057018

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Confirm your engine model/year in the table below.

Brand Model Rated HP Stroke Years OEM Part No. Notes
MerCruiser 4.3L V6 140-200 4-Stroke 1963-2014 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 Specifications

Specification Value
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
Fitting Type Brass fittings with hose connections
Warranty Varies by manufacturer - JLM Marine offers lifetime warranty
Other Technical Attributes Bi-directional flow, compatible with steel and composite timing chain covers

Package Contents

  • 1 x Water Circulation Pump (8503991/8M0113734)

Explosion Diagram

Installation Guide

  1. Disconnect Battery: Ensure the engine is off and disconnect the negative battery terminal.
  2. Drain Coolant: Place a catch pan under the engine and drain the cooling system.
  3. Loosen Belt: Loosen the tensioner to remove the serpentine belt from the water pump pulley.
  4. Remove Hoses: Carefully disconnect the inlet and outlet hoses from the water pump.
  5. Unbolt Old Pump: Remove the mounting bolts securing the old water pump to the engine block.
  6. Clean Surface: Thoroughly clean the engine block's mounting surface to remove any old gasket material or sealant.
  7. Install New Pump: Position the new gasket and water pump onto the engine block and hand-tighten the bolts.
  8. Torque Bolts: Tighten the mounting bolts to the manufacturer's recommended torque specifications.
  9. Reconnect Components: Reattach the hoses and reinstall the serpentine belt, ensuring proper tension.
  10. Refill System: Fill the cooling system with the appropriate coolant mixture.
  11. Check for Leaks: Reconnect the battery, start the engine, and carefully check for any leaks around the pump and hoses.

Troubleshooting & FAQ

How do I confirm this fits my engine?
This pump is designed for a wide range of MerCruiser, Volvo Penta, and OMC engines. A critical exception is that it will NOT fit 2007 and newer MerCruiser V6 4.3L engines that lack a water bypass hole. Please verify your engine model, year, and part number against the compatibility tables above.

What are the signs of a failing water pump?
Common symptoms include coolant leaks from the pump itself, an engine that is overheating, a loose or noisy water pump pulley, or steam coming from the engine compartment.

What does "bi-directional" mean?
A bi-directional pump can operate correctly regardless of the engine's rotational direction (clockwise or counter-clockwise), making it versatile for different engine setups.

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.
Shipping Notes
  • Free Standard Shipping on $100+ Orders to the USA.
  • Except Preorder products are shipped in 48 hours.
  • Delivery to the USA:
  1. Standard Shipping : 3-10 business days
  • If time is of the essence, please consider selecting expedited delivery for faster service.
Exchange/Return Notes
  • We offer a 30-day return/exchange service after receiving.
  • Final sale items are not eligible for returns or exchanges.
  • To process your return/exchange, please contact us at [email protected]
  • Please click here for more details>>> Return & Exchange Policy
SKU: 53102274791

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4.2 ★★★★★
Based on 19 reviews
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Product Reviews
S
Verified Purchase
Skylar Hartnett
Lexington, US
★★★★★ 5
It works to divide a room, but it's not easy to use.
Color: Grey, Size: 6 Panel
This comes in multiple pieces and you have to build every single piece including the cloth that is between the two poles. There are plastic clips to hold the sections together, but they easily come off if you move the dividers the wrong way or try to reposition it. The only thing holding it up is rectangular shaped feet on the bottom and they are a pain when you hit it with your toes. It works if you need to divide a room, but its not pretty and there are far better options. It's cheaply made and has a habit of falling down if you are trying to use it in a straight or slightly angled line.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on December 26, 2022
A
Verified Purchase
Amazon Customer swengelp
Los Angeles, US
★★★★★ 4
Nice divider
Color: Black, Size: 6 Panel
Nice divider. Set up is a bear. I am a bit concerned with stability. Overall I like it.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on March 12, 2026
N
Verified Purchase
Nay from the Bay
Port Orchard, US
★★★★★ 5
Great privacy room divider
Color: Black, Size: 6 Panel, Color: Black, Size: 6 Panel
I got this room divider for our game room that shares the garage/laundry room, to separate the spaces. I was happy that it was relatively easy to put together in less than an hour with nothing more than a screwdriver (provided) although I used a small handheld drill. The instructions were pretty straightforward and easy to understand as everything was labeled. I have 2 small grandkids at home running around while I put this together so my timeline to completion might be longer than others. It recommends 2 people to assemble, but I was able to complete alone in about 40 minutes total and as I said I used a small handheld drill, (although it does come with a small Philips screwdriver) which is the only tool you need for assembly. The first two panels took me about 20 minutes but the other 4 were simple repeats after the initial 2. After all 6 panels were assembled the plastic clips to piece them together were literally a "SNAP" to put on. The poles are made of metal and the panels are made of a very sturdy almost canvas like fabric. When held up to the light not a lot shined through so very good for privacy. You can snap them together in sections and have 2 separate panels of 3 or what ever configuration you want. They are easy to move and bend around furniture or other obstacles, also fold flat together if you need to put them aside for storage. This worked out just as we had planned, very easy to move around when needed and I am very happy with this product. I loved how simple it was to put together, easy instructions, and the durability and functionality of it.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on December 29, 2024
R
Verified Purchase
robert ferrell
Natrona Heights, US
★★★★★ 5
Good
Color: Black, Size: 6 Panel
Love it , just what so needed , easy to put together (some what ) …
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Reviewed in the United States on May 16, 2026
C
Verified Purchase
Crimm
Lake Worth, US
★★★★★ 3
Decent for the price. Instructions suck but most people should be able to figure it out. More below.
Color: Black, Size: 6 Panel, Color: Black, Size: 6 Panel
SUMMARY: 3 stars from me because it's firmly average. It's fine for the price. Assembly and materials are alright but I can see some caveats depending on your circumstances. Assembly instructions do a subpar job of pointing out some details. ASSEMBLY INSTRUCTIONS: Maybe it's because I'm autistic and/or building model kits and assembling stuff is my jam, but I honestly thought people were exaggerating when they were complaining about the instructions and I'd be able to flex my ~superior assembly skills.~ I was wrong! These instructions genuinely suck, and whoever is responsible for making them should be ashamed. The instructions do a poor job of calling out some details regarding orientation of parts, and some of the images do not actually match the physical parts. For example, it does not really outline the assembly of the end panels clearly, and I can see someone accidentally using the wrong poles. I've drawn over a photo to show what you should do to try and make it clearer. Additionally, the manual shows a flathead screw for bolting the feet into position, but the actual screw is not a flathead. It also does not point out the counterbore, so if you aren't paying attention you may put the foot pads onto the wrong side of the foot. It's also missing the fact that you need to use another one of the plastic pieces when you finish assembling a panel. ACTUAL ASSEMBLY & MATERIALS: To their credit, all of my bags were clearly labeled. The assembly process wasn't difficult. It's mostly just tedious and requires a fair amount of space. I was able to assemble it by myself without any real difficulty. However, the way it's assembled means two things. One, the fabric parts aren't removable without disassembly. So if you want to use this in an environment where they would require cleaning, I would seriously recommend looking for another option. Or, you could buy this just to use the frame pieces and then somehow buy or make your own fabric pieces designed to be removable with velcro or something. Two, because of the materials I really don't have a lot of faith in this thing surviving disassembly and reassembly. Like a lot of sorta-cheap-but-convenient furniture, it uses those spring-button connections and plastic inserts with self-tapping screws. Those things are not really meant to be disassembled and rethreaded. It also relies a lot on the tension of the poles and the fabric to keep everything rigid and squared, which I think puts a lot of pressure on the aforementioned buttons, plastic inserts, and the hollow metal rods. So I feel like that will also cause issues with disassembly and reassembly. Basically once this thing is assembled, it's not really meant to be disassembled. The best you can do is spot-clean the fabric if you need to. Speaking of the fabric, I didn't see any labels on them or anything in the manual that says what they are, but they feel like some kind of polyester. They generate static electricity pretty easily, and pet hair and debris sticks easily. So that's another downside of them not being easily removable. For the most part it does seem pretty stable. The poles seem to be pretty uniform in length so they're all making contact with my floor. Obviously this isn't structural so it shouldn't be supporting anything, but the two main feet seem to be doing fine with keeping this thing upright. CLOSING THOUGHTS: Really, it's fine for what it is, but it could be better in a lot of little ways and the substandard quality of the instructions just seems unprofessional to me, which is why I'm being so harsh with my rating. Depending on your needs and environment you may want to consider a different option. Preferably one that is made to be disassembled with better materials, and/or one with fabric pieces made to be removed easily.
WAS THIS REVIEW HELPFUL?YesReportShare
Reviewed in the United States on May 28, 2023

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