Impeller for Yamaha/Mariner 20D & 25 HP – Precise OEM Replacement for Small Engines

This small but crucial impeller is made for Yamaha 20 HP (model 20D) and Yamaha/Mariner 25 HP two-stroke outboards. Despite the lower power of these engines, keeping them properly cooled is just as important as for bigger ones. The 52.400.08 impeller (CEF code 500384) ensures that even compact engines run at optimal temperature without risk of overheating. It directly replaces the original Yamaha part #6L2-44352-00, which was used in the aforementioned models in the 1980s and 1990s.

• Compatibility: It’s primarily intended for Yamaha 20D (20 HP, 2-stroke) – Yamaha’s ‘D’ designation suggests the mid-90s when this engine was current – and for Yamaha 25 HP 2-stroke from similar years, especially those of smaller displacement (twin-cylinder 25s). Mariner versions: If you have a Mariner 25HP from the 90s that is essentially a Yamaha in design (many were), this impeller fits that as well. For further reference, the same OEM part number (6L2-44352-00) was used in some Selva/Yamaha 15–25 HP models as well (Selva might have different model names but internally Yamaha). In summary, this impeller serves the “small” series water pumps for Yamaha outboards.
• Use Cases: 20–25 HP motors are typically found on small boats: 3–4 m inflatables, foldable fishing boats, canoes with transom mounts, or as auxiliary kicker engines on larger vessels. These engines often run for extended periods at low throttle (e.g., trolling for fish) or as backup motors on sailboats – scenarios where cooling still needs to be effective even if the load is different. The impeller provides adequate water circulation even when idling or running slowly, so the engine doesn’t overheat on hot days or when water flow is limited (shallow water operations). For example, if you’re trolling all afternoon in summer heat, this impeller helps ensure your 20HP stays cool the whole time.
• Performance: The 6-blade design here is optimized for the small diameter pump: this impeller has approximately an outer diameter of ~45 mm and an inner hub around 13.97 mm, matching the original. Despite its compact size, the 6 blades achieve good pumping performance. The impeller quickly creates the vacuum to draw water in and the pressure to push it through the engine. This is key because small engines typically don’t have thermostats or complex cooling systems – the impeller is the main component governing cooling. With a new impeller, your 20–25 HP engine will have a strong, steady tell-tale stream and a much lower risk of hot spots in the cylinder. In fact, you might notice the engine idles smoother or doesn’t stall as easily if it was running hot before.
• Quality: Manufactured to Yamaha’s standards, the impeller is made of material resistant to gasoline traces and oil – small engines often don’t have a separate closed cooling (heat exchanger), but use raw water that can contain exhaust residues. The nitrile rubber (NBR) used for this impeller handles such an environment better than ordinary rubber. Additionally, the material stays flexible in cold water – important if you run the motor in early spring or late fall when water temperatures are low; the impeller won’t stiffen up too much and will continue to function effectively. The hub is securely bonded, and the overall construction is geared toward longevity, meaning you can trust this little part to do its job season after season.
• Maintenance: Small motors often get used in less-than-ideal conditions – shallows, weedy areas, or silty rivers – where the impeller might suck up fine grit. Therefore, if you operate your boat in such conditions, inspect the impeller more frequently. One symptom of an issue can be the engine stalling at idle – sometimes the cause is overheating due to weak cooling flow. Recommendation: replace the impeller every year or at most every two years, as it’s an inexpensive part and replacement is relatively easy. Always keep a spare impeller for your small engine – it takes up little space but can save your fishing weekend if the old one fails. When changing it, carefully check inside the pump housing for sand or wear; clean out any debris before installing the new impeller so it runs on a smooth surface. By following these practices, you’ll keep your 20D/25HP running cool and strong, ready to putter around or get you home when needed.