Yanmar 2GM20 Water Pump Impeller Replacement
A worn impeller on your Yanmar 2GM20 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 GM20
Disassembling a Yanmar 2GM20 sea water pump at sea
Replacing a Yanmar 2GM20 Sea Water Pump Impeller
Tools Needed
- Adjustable pliers (water pump pliers)
- Vice grips or channel locks
- Flathead screwdriver
- File or chisel
- Socket and nuts (larger than the flange on the shaft)
- Wood piece or bench
Safety
- Be careful not to damage threads while removing parts.
- Wear gloves to protect hands from sharp edges.
Steps
- Remove the faceplate of the water pump using a screwdriver.
- Use adjustable pliers to grip and remove the impeller.
- If the impeller is stuck, use vice grips or channel locks to apply more force.
- If necessary, file or grind off the keyway in the pulley to remove it.
- Once the impeller and pulley are removed, locate the bearing cover and gently remove it.
- Remove the bearings from the shaft using a socket and nuts, protecting the shaft with a wood piece or bench.
- Clean the journal where the seal fits using washing liquid to ensure a smooth surface for the new seal.
- Install the new seal without lubricant.
- Reassemble the water pump, ensuring the new pulley keys onto the shaft properly.
Tips
- Carry spare impellers, bearings, seals, and shafts on board for repairs at sea.
- Regular maintenance before going to sea can prevent issues.
- If the shaft is damaged or bearings are worn, consider replacing them as well.
Which part do I need for my Yanmar 2GM20?
For most 2GM20 owners the part above (104211) 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 | |
|---|---|---|
| 104511 | Yanmar, Water Pump Belt, 104511-78780 | Find on Amazon → |
| 121000 | Yanmar, Cooling Water Pump Gasket, 121000-42052 | Find on Amazon → |
| 124223 | Yanmar, Cooling Water Impeller, 124223-42092 | Find on Amazon → |
| 128296 | Yanmar, Cooling Sea Water Impeller, 128296-42070 | Find on Amazon → |
| 128397 | Yanmar, Cooling Water Pump Assembly, 128397-42500, 128397-42501 | Find on Amazon → |
| 128695 | Yanmar, Cooling Fresh Water Pump Assembly, 128695-42010 | Find on Amazon → |
| YAN124223-42092 | IMPELLER | Find on Amazon → |
| YAN124223-42110 | IMPELLER GASKET | Find on Amazon → |
Many of these are the same physical part under different brand numbers. Confirm against your engine plate before ordering.
Frequently asked questions
What water pump impeller fits a Yanmar 2GM20?
The Yanmar 2GM20 uses the impeller sold as 104211, 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 2GM20?
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 2GM20?
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 2GM20, 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 2GM20?
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 3YM30 water pump / impeller
- All Yanmar water pump guides
- Free Yanmar boat valuation
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