A reliable water pump is essential to an outboard engine's cooling system. The impeller, housing, wear surfaces and related hardware all work together to move cooling water through the engine while it is running.

When it is time to service the water pump on a compatible Yamaha 15 or 20 HP four-stroke outboard, replacing the complete assembly can make more sense than changing only the impeller—especially if the existing housing and wear surfaces have already seen substantial use.

The JLM Marine water pump impeller kit covered in this review is an aftermarket replacement designed for specific Yamaha 15 HP and 20 HP four-stroke outboards. It cross-references Yamaha water pump kit numbers including 6AH-W0078-00-00, 6AH-W0078-01-00 and 6AH-W0078-02-00.

Rather than supplying only a rubber impeller, the kit contains the major components needed for a more complete water-pump service.

Let's look at what's included, compatibility, component construction and the points you should check before ordering.

Review note: Blog60s has not conducted hands-on flow-rate, cooling-performance, material, corrosion or long-term durability testing of this water pump kit. This review is based on manufacturer product information and the supplied product images. Manufacturer performance and quality statements should not be interpreted as independent Blog60s test results.

JLM Marine Yamaha 15–20 HP Water Pump Kit Overview

The first image shows why this product is better described as a water pump kit rather than simply an impeller.

The package includes the black flexible impeller along with the pump housing, metal cup, wear plate, seals and installation hardware.

This is important because an aging water pump can have wear beyond the impeller itself.

The surfaces surrounding the impeller can become worn or damaged over time, while seals and related components may also deteriorate.

Replacing the complete set allows multiple service components to be addressed during the same lower-unit service.

What's Included?

The supplied images show a fairly comprehensive collection of water-pump components, including:

  • Flexible water-pump impeller
  • Water-pump housing
  • Stainless-steel cup/insert
  • Wear plate
  • O-ring and sealing component
  • Mounting bolts
  • Metal retaining pieces
  • Drive key and small installation hardware

The exact purpose and orientation of the smaller pieces should be confirmed against the appropriate Yamaha service documentation during installation.

This is preferable to guessing based solely on their appearance.

The kit's broad component coverage is one of its main advantages compared with buying only a replacement impeller.

The Water Pump Impeller

The black flexible impeller is the component most owners immediately associate with outboard water-pump maintenance.

Its flexible blades rotate inside the pump housing and help draw and move cooling water through the system.

Because the blades operate while bent against the internal pump surface, the impeller is a wear component.

Age, operating conditions, storage and running conditions can all affect its condition.

Visible deterioration can include damaged, permanently deformed or missing blades, but an impeller should not be judged only by whether it still looks intact.

Service intervals and the condition of the complete cooling system also matter.

One advantage of this JLM Marine kit is that the new impeller is paired with new surrounding pump components rather than being expected to operate against potentially worn original surfaces.

Stainless-Steel Pump Cup

The stainless-colored circular component forms an important working surface around the impeller.

The supplied close-up makes its shape easier to see, including the central opening and water passage.

During operation, the flexible impeller blades work within this area.

That relationship means the condition of the pump cup matters.

If an existing cup is significantly scored, damaged or worn, installing only a fresh impeller may leave another worn component in the water-pump assembly.

A complete kit addresses that concern by supplying a replacement cup along with the impeller.

Water Pump Wear Plate


The kit also includes a metal wear plate.

This component provides another surface associated with the water-pump assembly and includes the openings required for the pump and cooling-water passages.

As its name suggests, the wear plate is a component worth inspecting during water-pump service.

Scoring or other deterioration on an old plate may be a reason to replace it instead of automatically reusing it with a new impeller.

Having a new plate included is therefore a meaningful advantage of a full repair kit.

Housing and Internal Pump Surfaces


The housing image shows how the metal cup fits into the light-colored outer pump housing.

This gives a clearer picture of the relationship between the components than the complete-kit photograph alone.

The housing provides the structure for the water-pump assembly, while the internal metal surfaces provide the environment in which the impeller operates.

Replacing these components together can be useful when servicing an older pump where the condition of the original assembly is uncertain.

It also avoids relying on a new impeller to compensate for badly worn surrounding components.

A Closer Look at the Housing and Inserts

This image separates the outer housing from the metal components and provides another useful view of the pump's construction.

For buyers comparing an impeller-only replacement with a complete kit, this illustrates the difference clearly.

An impeller-only service addresses one primary wear component.

A complete kit gives you the opportunity to renew several of the surfaces and supporting parts at the same time.

That does not mean every water-pump service automatically requires every component to be replaced.

The correct decision depends on the service schedule, inspection of the existing parts and the requirements for the specific engine.

Yamaha Part Numbers and Compatibility

Fitment is one of the most important considerations when purchasing an outboard repair part.

JLM Marine markets this kit for compatible Yamaha 15 HP and 20 HP four-stroke outboard engines and cross-references water-pump kit numbers including:

  • 6AH-W0078-00-00
  • 6AH-W0078-01-00
  • 6AH-W0078-02-00

Those part numbers are much more useful for confirming compatibility than horsepower alone.

Two Yamaha outboards can share the same horsepower rating while belonging to different model families or production periods.

For that reason, do not purchase the kit simply because the cowling says "15" or "20."

Check the exact model, serial information and applicable Yamaha part number first.

If your existing parts documentation identifies one of the replacement numbers listed for this kit, that provides a stronger indication of compatibility.

Why a Complete Water Pump Kit Can Make Sense

There are two basic approaches when servicing an outboard water pump.

The first is replacing only the impeller.

That can be appropriate when the surrounding components are still within specification and the maintenance procedure calls only for the impeller.

The second approach is replacing multiple water-pump components together.

This becomes more attractive when the pump has accumulated significant use, its service history is unknown, or inspection reveals wear on the housing, cup or plate.

The JLM Marine kit is aimed more toward this second type of service.

Instead of receiving one rubber component, you receive a collection of parts that allows more of the pump assembly to be renewed.

Installation Considerations

Water-pump replacement on an outboard typically requires access to components in the lower-unit area, so this is not the same as replacing an easily accessible external filter.

Correct assembly matters.

The orientation of the impeller, key, pump surfaces, seals and hardware must match the requirements for the specific Yamaha engine.

Likewise, fasteners need to be tightened according to the appropriate service specifications.

Blog60s intentionally does not provide generic torque values here.

Torque specifications can vary by engine and fastener, and using a number from another model could result in improper installation or component damage.

Use the correct Yamaha service documentation for your exact engine model and production range.

If you do not have the tools or experience required to remove and reinstall the lower unit correctly, professional marine service is the safer option.

Important Checks During Installation

Before assembling the new pump, inspect the surrounding area rather than treating the job as a simple parts swap.

Check the old impeller for missing pieces.

If part of an impeller blade has broken away, simply installing a new impeller does not explain where the missing material went.

The old housing and wear surfaces should also be inspected for unusual scoring, debris or other signs of trouble.

Make sure sealing surfaces are clean and install the supplied components in the correct orientation.

After reassembly, verify cooling-system operation according to the manufacturer's service procedure before assuming the job is complete.

Aftermarket vs Yamaha OEM

The JLM Marine kit is an aftermarket replacement, not a genuine Yamaha OEM water-pump kit.

For some owners, that distinction will determine the buying decision immediately.

Owners who prefer genuine Yamaha service components should use the appropriate OEM parts for their engine.

For buyers comfortable with aftermarket maintenance components, the attraction is usually the combination of price, parts coverage and convenience.

The important point is not to treat an aftermarket cross-reference as permission to skip fitment verification.

The replacement part numbers, engine model and applicable service information should still match.

Blog60s has not independently compared the materials, dimensions or service life of this kit against a genuine Yamaha water-pump kit.

Advantages of the JLM Marine Kit

The most obvious advantage is completeness.

The kit goes beyond an impeller-only replacement and includes multiple components involved in the water-pump assembly.

The separate housing, cup and wear plate shown in the product images can be particularly useful when the original pump surfaces are no longer in ideal condition.

Another advantage is the clear OEM-number cross-referencing.

For owners who already know the Yamaha water-pump kit number required by their engine, matching the replacement number is more reliable than shopping by horsepower alone.

Potential Drawbacks

The first consideration is that this is an aftermarket product.

Buyers specifically seeking genuine Yamaha components will need an OEM alternative.

The second is fitment.

The "15–20 HP" description should not be interpreted to mean every Yamaha outboard in that horsepower range uses this kit.

The third limitation is independent performance data.

Blog60s has not measured cooling-water flow, dimensional tolerances, impeller material properties or service life for this kit.

For that reason, we would not claim that it lasts longer, pumps more water or performs identically to Yamaha OEM parts without controlled comparative testing.

Impeller-Only Replacement vs Complete Kit

If your water pump is being serviced regularly and all surrounding components remain in good condition, an impeller-only replacement may be sufficient depending on Yamaha's service requirements.

A complete kit becomes more compelling when you find wear on multiple pump components or when the service history is unknown.

It can also make sense during a more comprehensive lower-unit maintenance session because the pump is already being disassembled.

The best choice is therefore not automatically "replace everything."

Inspect the components and follow the service information applicable to the engine.

How Does This Fit Into Outboard Cooling Maintenance?

The water pump is only one part of an outboard's cooling system.

It is responsible for moving cooling water, while other components—including the thermostat and internal cooling passages—also influence engine temperature.

A weak cooling-water flow or overheating condition therefore should not automatically be blamed on one component without diagnosis.

This is particularly important for owners troubleshooting an existing cooling problem rather than performing routine preventive maintenance.

Blog60s has also reviewed JLM Marine water-pump and thermostat components for compatible Mercury outboards, which can be useful for readers researching similar cooling-system maintenance on other engine families.

Is the JLM Marine Yamaha 15–20 HP Water Pump Kit Worth Considering?

For the correct Yamaha application, this kit has a practical advantage over buying only an impeller: it allows more of the pump assembly to be serviced at once.

The supplied product images show a comprehensive group of components including the impeller, housing, metal pump surfaces, seals and installation hardware.

That makes it particularly relevant when an existing water pump has more wear than a simple impeller replacement can address.

The deciding factor should still be compatibility.

Confirm the Yamaha part number and exact engine application before ordering.

If the numbers match and you are comfortable using aftermarket maintenance components, the JLM Marine kit provides a convenient complete-kit approach to Yamaha 15–20 HP water-pump service.

Frequently Asked Questions

Is this a genuine Yamaha water pump kit?

No. It is an aftermarket replacement sold by JLM Marine.

Does the kit include the impeller?

Yes. The supplied product images show the flexible black water-pump impeller as part of the kit.

Does it include the water pump housing?

Yes. A replacement outer pump housing is included along with the internal metal pump components.

Which Yamaha part numbers does it replace?

JLM Marine cross-references the kit with Yamaha numbers including 6AH-W0078-00-00, 6AH-W0078-01-00 and 6AH-W0078-02-00.

Will it fit every Yamaha 15 HP or 20 HP outboard?

Do not assume so.

Compatibility should be confirmed using the exact engine model and applicable Yamaha part number rather than horsepower alone.

Is a complete kit better than replacing only the impeller?

It depends on the condition of the existing pump.

A complete kit is useful when the housing, cup, wear plate or other components also need replacement. If those components remain serviceable, an impeller-only service may be appropriate depending on the manufacturer's maintenance requirements.

Can I install the kit myself?

Experienced owners with the correct tools and Yamaha service documentation may choose to perform water-pump maintenance themselves.

Because the job involves lower-unit removal and correct pump assembly, owners who are uncertain about the procedure should use a qualified marine technician.

Final Thoughts

The JLM Marine Yamaha 15–20 HP Water Pump Kit offers something more useful than a standalone replacement impeller: a collection of components for servicing a larger portion of the pump assembly.

The included impeller, housing, cup, wear plate, seals and hardware make it particularly relevant when the existing pump shows broader wear or has an uncertain maintenance history.

At the same time, this is an aftermarket component and Blog60s has not independently tested its cooling performance or long-term durability against Yamaha OEM parts.

The most important step comes before installation: verify the exact Yamaha engine application and replacement part number.

If the fitment matches, the kit provides a straightforward option for owners who want to perform a more comprehensive water-pump service rather than replacing only the impeller.