Mercury 70 HP Water Pump Impeller Replacement
A worn impeller on your 70 hp Mercury 70 HP starves the engine of cooling water and can overheat it in minutes. Below is the water-pump kit we recommend, which 70 HP 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 Mercury 70 HP
how to install a water pump on a 1980 mercury 70 hp
Tools Needed
- Screwdriver
- Prying tool
- White lithium grease
Safety
- Ensure the engine is cool before starting the replacement.
- Be careful when handling the impeller to avoid damaging it.
Steps
- Remove the three screws securing the cap using a screwdriver.
- Gently pry the cap off and remove the washer underneath.
- Carefully lift out the old water pump, ensuring the impeller does not get damaged.
- Inspect the old impeller for straightness; if it is not straight, it is unusable.
- Apply a small amount of white lithium grease to the impeller to help it stick and stay in place.
- Apply more white lithium grease to the shaft of the new water pump.
- Insert the new water pump, ensuring the groove on the pump lines up with the bump on the keyway.
- Clean any dirt from the seal area to ensure a proper fit.
- Apply more white lithium grease to the inside of the seal area.
- Install the new water pump, pushing down and turning it clockwise simultaneously.
- Replace the washer and cap, securing it with the three screws.
Tips
- Use white lithium grease to help the impeller stick and stay in place.
- Ensure the groove on the pump lines up with the bump on the keyway for proper installation.
- Clean any dirt from the seal area to prevent the impeller from getting stuck to the shaft.
Which part do I need for my Mercury 70 HP?
For most 70 HP owners the part above (12010) 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 (53)
| Part number | Description | Fits | |
|---|---|---|---|
| 12094 | Impeller Kit | 70 HP (3-cyl.) | cross-reference only |
| 12100 | Impeller | 70 HP (3-cyl.) | cross-reference only |
| 12180 | Impeller | 70 HP (3-cyl.) | cross-reference only |
| 12250 | Impeller Kit | 70 HP (3-cyl.) | cross-reference only |
| 12420 | Water Pump Upper Housing | 70 HP (3-cyl.) | cross-reference only |
| 18-1346 | For: 3.5-9.8 HP & Mercruiser, For: 75-125 3 & 4 cyl. belt driven water pump | 70 | Find on Amazon → |
| 18-3007 | Impeller / water-pump component | 70 | Find on Amazon → |
| 18-3017 | Impeller / water-pump component | 70 | Find on Amazon → |
| 18-3056 | Impeller / water-pump component | 70 | Find on Amazon → |
| 18-3069 | Sierra 18-3069 | 70 | Find on Amazon → |
| 18-3107 | Sierra 18-3107 | 70 | Find on Amazon → |
| 18-3115 | Sierra 18-3115 | 70 | Find on Amazon → |
| 18-3117 | Sierra 18-3117 | 70 | Find on Amazon → |
| 18-3118 | Sierra 18-3118 | 70 | Find on Amazon → |
| 18-3200 | For: 75-90 HP | 70 | Find on Amazon → |
| 18-3204 | Sierra 18-3204 | 70 | Find on Amazon → |
| 18-3207 | Sierra 18-3207 | 70 | Find on Amazon → |
| 18-3214 | Impeller for Honda BF75A | 70 | Find on Amazon → |
| 18-3217 | Sierra 18-3217 | 70 | Find on Amazon → |
| 18-3423 | Sierra 18-3423 | 70 | Find on Amazon → |
| 18-3424 | Sierra 18-3424 | 70 | Find on Amazon → |
| 18-3517 | Sierra 18-3517 | 70 | Find on Amazon → |
| 30-43011 | Mercury OEM 30-43011 (replaces Sierra 18-1346) | 70 | Find on Amazon → |
| 30-43011T | Mercury OEM 30-43011T (replaces Sierra 18-1346) | 70 | Find on Amazon → |
| 324351 | Mercury OEM 324351 (replaces Sierra 18-3117) | 70 | Find on Amazon → |
| 32768 | Mercury OEM 32768 (replaces Sierra 18-3107) | 70 | Find on Amazon → |
| 43024A7 | Mercury OEM 43024A7 (replaces Sierra 18-3214) | 70 | Find on Amazon → |
| 478M0100526 | Mercury OEM 478M0100526 (replaces Sierra 18-3214) | 70 | Find on Amazon → |
| 48753 | Mercury OEM 48753 (replaces Sierra 18-3115) | 70 | Find on Amazon → |
| 49771 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 64286 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 71109 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 72083 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 73640T01 | Mercury OEM 73640T01 (replaces Sierra 18-3423) | 70 | Find on Amazon → |
| 76281 | Mercury OEM 76281 (replaces Sierra 18-3204) | 70 | Find on Amazon → |
| 77177A1 | Mercury OEM 77177A1 (replaces Sierra 18-3424) | 70 | Find on Amazon → |
| 77822A1 | Mercury OEM 77822A1 (replaces Sierra 18-3118) | 70 | Find on Amazon → |
| 80501 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 81423M | Mercury OEM 81423M (replaces Sierra 18-3069) | 70 | Find on Amazon → |
| 879124 | Mercury OEM 879124 (replaces Sierra 18-3069) | 70 | Find on Amazon → |
| 89630 | Water Pump Upper Housing | 70 HP (3-cyl.) | cross-reference only |
| 89830 | Water Pump Upper Housing | 70 HP (3-cyl.) | cross-reference only |
| 89983Q1 | Mercury OEM 89983Q1 (replaces Sierra 18-3207) | 70 | Find on Amazon → |
| 89983T | Mercury OEM 89983T (replaces Sierra 18-3007) | 70 | Find on Amazon → |
| 8M0100526 | Mercury OEM 8M0100526 (replaces Sierra 18-3214) | 70 | Find on Amazon → |
| 8M0204677 | Mercury OEM 8M0204677 (replaces Sierra 18-3117) | 70 | Find on Amazon → |
| 8M0214942 | Mercury OEM 8M0214942 (replaces Sierra 18-3204) | 70 | Find on Amazon → |
| 8M6010328 | Mercury OEM 8M6010328 (replaces Sierra 18-3069) | 70 | Find on Amazon → |
| 8M6013130 | Mercury OEM 8M6013130 (replaces Sierra 18-3069) | 70 | Find on Amazon → |
| 91969 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 93859 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 95890 | Water Pump Service Kit | 70 HP (3-cyl.) | cross-reference only |
| 97108M | Mercury OEM 97108M (replaces Sierra 18-3069) | 70 | 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 Mercury 70 HP (70 hp)?
The Mercury 70 HP uses the impeller sold as Sierra 18-1346, plus its OEM and aftermarket cross-references (53 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 Mercury 70 HP?
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 Mercury 70 HP?
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 70 HP, 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 Mercury 70 HP?
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
- Mercury 60 HP water pump / impeller
- Mercury 115 HP water pump / impeller
- Mercury 75 HP water pump / impeller
- Mercury 90 HP water pump / impeller
- All Mercury water pump guides
- Free Mercury boat valuation
- Buying a boat? Check whether the asking price is fair
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