Impellers are essential components of an outboard motor's cooling system. They are small rubber fans with flexible blades located inside the water pump and used to push coolant through the engine. A well-maintained impeller ensures proper cooling system operation, preventing overheating and engine damage.
Function of the Impeller in the Outboard Motor
The impeller is located inside the water pump , usually located in the outboard motor's lower leg. When the engine is running, the impeller rotates and draws in water from the outside, circulating it through the cooling system to keep the engine at an optimal temperature.
If the impeller is worn or damaged, water flow decreases, causing the engine to overheat , which can lead to costly failures or even melted internal parts.
When to Replace the Impeller?
The impeller is subject to wear and must be replaced regularly. Some signs that indicate the need for replacement are:
✅ Decreased water flow from the engine exhaust
✅ Engine overheating
✅ Difficulty starting or sudden engine stalling
✅ Old or damaged impeller (recommended replacement at least every 1-2 years or every 100 hours of use)
If the engine has been unused for a long time, the impeller may have hardened or lost elasticity, reducing its effectiveness.
Types of Impellers for Outboard Motors
There are different types of impellers depending on the engine model. Some of the main outboard engine brands for which you can find replacement impellers include:
- Yamaha
- Mercury/Mariner
- Honda Marine
- Suzuki Marine
- Evinrude/Johnson
- Tohatsu/Nissan
Each impeller is designed to fit a specific engine model, so it is essential to verify the OEM part number or compatible part number before purchasing.
How to Replace an Outboard Motor Impeller?
🔧 Necessary Tools:
- Socket or English wrenches
- Screwdriver
- Marine fat
- Replacement impeller
- Pump gaskets (if necessary)
🔹 Replacement Steps:
1️⃣ Turn off the engine and disconnect the battery for safety.
2️⃣ Remove the motor foot : disassemble the lower part of the unit to access the water pump.
3️⃣ Remove the old impeller from the pump and check its wear condition.
4️⃣ Clean and lubricate the inside of the pump with marine grease.
5️⃣ Insert the new impeller , taking care to position the blades in the correct direction (usually following the direction of rotation of the crankshaft).
6️⃣ Reassemble the motor foot , making sure all gaskets are in good condition.
7️⃣ Test the motor to ensure that the water flow is smooth.
If you are unsure how to replace it, it is advisable to consult an experienced marine mechanic.
Tips for a Long Impeller Life
✔ Replace the impeller regularly , even if you don't notice a drop in performance.
✔ Avoid running the engine dry : the absence of water in the pump can quickly damage the impeller blades.
✔ Rinse the engine with fresh water after use at sea , to avoid salt deposits that could compromise the water pump.
✔ Check the cooling circuit periodically to prevent blockages or leaks.
