Yanmar 2GM20F Water Pump Impeller Replacement
A worn impeller on your Yanmar 2GM20F starves the engine of cooling water and can overheat it in minutes. Below is the water-pump kit we recommend, which 2GM20F 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 2GM20F
Yanmar 2GM20F Impeller Change ~ Ep 53
Tools Needed
- Ratchet
- 12 millimeter socket
- 7 millimeter socket
Safety
- Ensure the seacock is closed before starting the project to prevent water flooding.
Steps
- Close the seacock that allows seawater into the engine.
- Remove the pulley by loosening the two 12 millimeter bolts and marking their position for later adjustment.
- Remove the eight 7 millimeter bolts holding the plate to access the impeller.
- Use needle-nose pliers to carefully pull out the impeller, ensuring the key is not lost.
- Clean the housing and remove any remaining gasket material.
- Insert the new impeller, aligning the key, and then place the new gasket.
- Reattach the plate with the six 7 millimeter bolts, ensuring they are tight but not stripped.
- Reattach the raw water hose and tighten the hose clamp.
- Replace the belt, ensuring it is in the correct position.
- Tighten the two pulley bolts back to their marked positions.
- Open the seacock and start the engine to check for leaks.
Tips
- Use a C-clamp to catch water from the hose when removing it.
- Consider using dish soap to ease the insertion of the new impeller.
- Inspect the impeller every year or two, even if it appears to be in good shape.
Which part do I need for my Yanmar 2GM20F?
For most 2GM20F owners the part above (121000-42052) 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 (8)
| Part number | Description | Fits | |
|---|---|---|---|
| 121000-42100 | Yanmar, Cooling Fresh Water Pump Body Assembly, 121000-42100 | 2GM20F-YEU | Find on Amazon → |
| 124223-42092 | Yanmar, Cooling Water Impeller, 124223-42092 | 2GM20F | Find on Amazon → |
| 128296-42070 | Yanmar, Cooling Sea Water Impeller, 128296-42070 | 2GM20F | Find on Amazon → |
| 128397-42500 | Yanmar, Cooling Water Pump Assembly, 128397-42500, 128397-42501 | 2GM20F-YEU | Find on Amazon → |
| 128397-42501 | Yanmar, Cooling Water Pump Assembly, 128397-42501, 128397-42500 | 2GM20F-YEU | Find on Amazon → |
| 128695-42010 | Yanmar, Cooling Fresh Water Pump Assembly, 128695-42010 | 2GM20F-YEU | Find on Amazon → |
| YAN124223-42092 | IMPELLER | 2GM20F | Find on Amazon → |
| YAN124223-42110 | IMPELLER GASKET | 2GM20F | 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 2GM20F?
The Yanmar 2GM20F uses the impeller sold as 121000-42052, plus its OEM and aftermarket cross-references (8 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 2GM20F?
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 2GM20F?
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 2GM20F, 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 2GM20F?
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 3GM30 water pump / impeller
- Yanmar 2GM20 water pump / impeller
- Yanmar 2QM15 water pump / impeller
- All Yanmar water pump guides
- Free Yanmar boat valuation
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