Yanmar 3YM20 Water Pump Impeller Replacement
A worn impeller on your Yanmar 3YM20 starves the engine of cooling water and can overheat it in minutes. Below is the exact water-pump kit that fits this engine, 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 Impeller – Yanmar 2YM15
Yanmar 3YM20 Raw Water Pump Water Seal Replacement
Tools Needed
- Pliers
- Bent piece of metal or a prying tool
Safety
- Warning: Ensure the engine is turned off and cool before starting the procedure.
- Warning: Be prepared to catch any water that may spill out when removing the cover plate.
Steps
- Remove the cover plate from the water pump to expose the impeller.
- Using pliers, carefully grip and remove the impeller.
- Behind the impeller, locate the water seal, which has a groove facing towards the front.
- Using a bent piece of metal or a prying tool, carefully prise the water seal out from the back.
- Clean the groove where the water seal was located to ensure a proper fit for the new seal.
- Press the new water seal into place, ensuring it is properly seated in the groove.
- Reassemble the pump by placing the impeller back into position and securing it with the cover plate.
Tips
- Tip from the video: Replacing the water seal can be done without removing the bearings, making the procedure easier.
- Another tip: Regularly check and maintain the water pump to prevent excessive wear and tear, which can lead to more frequent replacements.
Which part do I need for my Yanmar 3YM20?
For most 3YM20 owners the part above (128990) is the right choice.
Frequently asked questions
What water pump impeller fits a Yanmar 3YM20?
The Yanmar 3YM20 uses the impeller sold as 128990. Confirm the number against your engine's model code and year plate before ordering.
How often should I replace the impeller on a Yanmar 3YM20?
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 3YM20?
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 3YM20, 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 3YM20?
For a competent DIYer it's typically a 1-2 hour job of medium difficulty. The step-by-step video above covers every step.
Related guides
- Yanmar 3GM30F water pump / impeller
- Yanmar 2GM20F water pump / impeller
- Yanmar 3GM30 water pump / impeller
- Yanmar 2GM20 water pump / impeller
- All Yanmar water pump guides
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