Yanmar 3YM30 Water Pump Impeller Replacement
A worn impeller on your Yanmar 3YM30 starves the engine of cooling water and can overheat it in minutes. Below is the water-pump kit we recommend, which 3YM30 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 3YM30
3YM30 Impeller Replacement
Tools Needed
- 7mm socket
- Screwdriver
- Stainless steel impeller puller
- Impeller kit (including new impeller, o-ring, screws, and glycerin lubricant)
Safety
- Close the seacock before starting the project to prevent water from leaking into the boat.
- Place a towel underneath to catch any dropped screws.
Steps
- Locate the C-cock at the bottom of the engine.
- Close the seacock to prevent water leakage.
- Remove the cushions from the birth and open the covers to access the saltwater pump.
- Use a 7mm socket to loosen the screws on the pump cover.
- Use a screwdriver to remove all the screws from the cover.
- Pull off the cover and be prepared for any minor leakage.
- Use a stainless steel impeller puller to remove the old impeller without damaging it.
- Clean up the gunk and dirt inside and around the cover.
- Replace the old gasket with a new one from the impeller kit.
- Lubricate the new impeller and the inside of the pump with glycerin.
- Insert the new impeller into the pump, which may take a few attempts.
- Use the new stainless steel screws from the kit to secure the cover back in place.
- Tighten the screws using the 7mm socket.
- Open the seacock before starting the engine.
- Start the engine and check for any leaks.
Tips
- It's a good idea to hold onto the old screws in case you drop one of the new ones.
- The job may take a couple of hours to complete.
Which part do I need for my Yanmar 3YM30?
For most 3YM30 owners the part above (YAN128990-42570) 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 | |
|---|---|---|---|
| YANX02173476 | IMPELLER O-RING | 3YM30 | 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 3YM30?
The Yanmar 3YM30 uses the impeller sold as 128990-42570, 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 3YM30?
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 3YM30?
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 3YM30, 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 3YM30?
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
- Free Yanmar boat valuation
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