Impeller for Yamaha/Mariner 25–50 HP – Versatile High-Quality Replacement

This impeller offers broad compatibility and high performance for outboard engines in the 25 to 50 HP range by Yamaha/Mariner. With a single product, you can service multiple different motors, making it especially valuable for repair shops or owners with more than one boat. The impeller is made by CEF and meets the specifications of Yamaha OEM 6H4-44352-00/02, which ensures easy installation and proper function.

• Compatibility:
  • Yamaha 2-Stroke: Suitable for classic 2-stroke models 25 HP, 30 HP, 40 HP, and 50 HP. For example, Yamaha 25B/30D models (from the 1980s/90s), 40N/40V from the ’80s, as well as 50D/50H models. All of these use impellers from the 6H4-44352 series.
  • Yamaha 4-Stroke: Compatible with early 4-stroke Yamaha F25 and F30 (25HP and 30HP), whose cooling systems were based on preceding 2-stroke designs. (Note: the later F40/F50/F60 use a larger impeller, covered earlier in the 40–70 HP category.)
  • Selva & Parsun: Many Selva engines in this class (25–50 HP) use Yamaha technology and parts – this impeller will fit the corresponding Selva models. Parsun/Hidea 40HP/50HP 4-strokes (Chinese brands based on Yamaha designs) also often use an equivalent of this impeller. In short, if the original impeller has a 6H4 or 663 code on it, this product is likely the correct replacement.
• Use Cases: Engines from 25–50 HP power small boats (3–5 m) – inflatable RIBs, jon boats, small fishing skiffs, aluminum boats, etc. Often these motors are used for short distances, but longer runs are not uncommon (for example, a 40–50 HP on a 5m boat crossing a lake or along a river). During long hours of mid-range cruising or sustained high-speed operation (carrying a load, getting on plane), a healthy impeller is critical for continuous cooling. This impeller ensures the engine gets the flow it needs to handle the thermal load.
• Performance: The impeller has 6 blades and dimensions (~16.1 mm inner, ~51.2 mm outer diameter) per the original design. This means it quickly draws in and pushes out cooling water through the system. Even at low RPM (like maneuvering at the dock or trolling), the cooling remains sufficient, and at high RPM the impeller maintains maximum flow. Thus, the engine stays within its optimal temperature range, which improves fuel efficiency and prevents detonation issues related to overheating. By maintaining stable cooling, you also ensure consistent performance and prevent power loss that can occur if an engine starts to overheat.
• Construction: CEF has used a high-resilience elastomer that combines flexibility and toughness. The impeller can withstand continuous spinning and water contact, even with minor particulates (silt or sand) to some extent. The metal hub of the impeller is firmly bonded, which ensures good transfer of torque from the driveshaft without slippage. This component is tested to perform in both freshwater and saltwater without premature corrosion or degradation. In essence, it’s built to last through the demands of active boating in diverse conditions.
• Maintenance: Replacing the impeller in this engine class is generally straightforward and is recommended every ~100 hours or once per season to be safe. Of course, if you notice a weaker cooling “tell-tale” stream or the engine running hotter than normal, replace the impeller immediately. The advantage of this versatile model is that you can keep it as a spare and use it for several different engines if needed. So with one impeller in your kit, you’re prepared to service your whole small fleet or help out a friend in a pinch. This flexibility and reliability make it an excellent part of your maintenance toolkit.