Yanmar 4JH110 Water Pump Impeller Replacement
A worn impeller on your Yanmar 4JH110 starves the engine of cooling water and can overheat it in minutes. Below is the water-pump kit we recommend, which 4JH110 variants it fits, a step-by-step video, and the parts you need to do the job yourself.
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Watch: how to replace it (step by step)
How to replace the water pump impeller on a Yanmar 4JH110
Yanmar Engine Basics 3 – belts & water pump
Tools Needed
- Screwdriver (to remove bolts)
- Hose (for back flushing)
- Bucket (to collect debris)
Safety
- Ensure the engine is turned off and cool before starting any work.
- Be cautious when handling and removing engine parts to avoid injury.
Steps
- Turn off the engine and allow it to cool.
- Remove the bolts on the front cover of the engine.
- Carefully lift off the front cover to expose the engine components.
- Locate the water pump and identify the impeller inside.
- If the impeller is damaged, remove the hose connected to the water pump.
- Insert a water hose into the removed hose and turn on the water.
- Place a bucket underneath the engine to collect any debris.
- Allow the water to backflush the system, removing any impeller chunks.
- If large pieces are still present, remove the hose from the back of the heat exchanger.
- Reattach the hose and continue backflushing until all debris is removed.
- Inspect the impeller to ensure all pieces are accounted for.
- Rebuild the impeller if all pieces are recovered.
- Reattach the front cover and secure it with the bolts.
Tips
- Regularly check the C-strainer to prevent debris from entering the water pump.
- Use a battery charger to properly charge multiple batteries, as the alternator may not be sufficient.
- Ensure all impeller pieces are removed to prevent engine overheating.
Which part do I need for my Yanmar 4JH110?
For most 4JH110 owners the part above (YAN129670-42610) is the right choice. Price tip: the aftermarket numbers are usually noticeably cheaper than the OEM-branded box — it is the same physical part. If you need an exact match, these compatible part numbers also fit:
Show all compatible part numbers (1)
| Part number | Description | Fits | |
|---|---|---|---|
| YANX0506590-01 | IMPELLER O-RING | 4JH110 | Find on Amazon → |
Many of these are the same physical part under different brand numbers. Build years are shown where our parts data has them. Where a variant has no years, only the model code is listed. Confirm against your engine plate before ordering.
Frequently asked questions
What water pump impeller fits a Yanmar 4JH110?
The Yanmar 4JH110 uses the impeller sold as 129670-42610, plus its OEM and aftermarket cross-references (1 compatible numbers are listed above). Confirm the number against your engine's model code and year plate before ordering.
How often should I replace the impeller on a Yanmar 4JH110?
Replace the water pump impeller every 1-3 years or roughly every 200-300 running hours, whichever comes first — and sooner if you run in silty, sandy or shallow water.
What are the symptoms of a failing impeller on a Yanmar 4JH110?
A weak or missing telltale stream, engine temperature climbing above normal, or an overheat alarm are the classic warning signs. A worn impeller can overheat and damage the engine within minutes, so don't delay the job.
Do I need the full water pump kit or just the impeller?
For the 4JH110, fit the complete kit. The seals, O-rings, gasket and wear plate age alongside the impeller, and replacing them together is the reliable, do-it-once job.
How long does a water pump job take on a Yanmar 4JH110?
For a competent DIYer it's typically a 1-2 hour job of medium difficulty. The video above shows the job on a similar Yanmar diesel engine — the procedure matches, but check the 4JH110 manual for model-specific details.
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