Johnson Pump 09-1027BT F5 Neoprene Impeller Kit

The impeller is the part that actually moves water through your raw-water cooling pump, and it's the one wear item in there that eventually gives up. This is the genuine Johnson Pump neoprene impeller for the F5 series pump. When yours starts losing vanes or your engine creeps up on temperature, this is the part that brings it back to life.

It's sized to the F5 housing and nothing else. 2-1/4 inch outer diameter, that's 57.1 mm, with a 1.24 inch (31.5 mm) width. The hub uses inner splines, so it slides straight onto the F5 pump shaft and grips without a key or a set screw. If you've got a Johnson F5 pump on your engine's cooling circuit, this drops right in. If you're not sure which pump you've got, pull the end cover and measure the old impeller before you order. The size on the vane pack should match.

The vanes are neoprene, the MC97 compound Johnson uses for standard engine-cooling and raw-water duty. Neoprene is the everyday choice for cooling water. It stays flexible, primes fast, and moves plenty of water at low RPM, which is exactly when your engine is asking for it at idle and low speed. Like every flexible impeller, it's a scheduled wear part. Most folks pull it once a season or at the first sign of running warm, and keep the old one aboard as a backup while it's still serviceable.

How do you know it's time? Rising engine temp is the big one. A weak or missing telltale stream is another. And when you pull the end cover and find vanes that are cracked, taken a set, or snapped clean off, that impeller's done. Don't nurse it. A tired impeller can strand you, and the pieces have to go somewhere.

The F5 is a common little pump. You'll find it moving engine cooling water on a range of marine engines, and Johnson's F-series pumps get put to work for everything from cooling to bilge and deckwash duty across the fleet. Whatever yours is doing, the impeller is what makes it pull, so it pays to keep the cooling side honest.

Installation is straightforward if you take your time. Line up the inner splines with the shaft and work the impeller in with a gentle rotation so every vane bends the same direction. A little glycerin or dish soap on the vanes helps it seat and gives it something to prime against on that first start. Never spin the pump dry. A flexible impeller cooks itself in under a minute with no water to lubricate and cool it, so make sure the pump will see water before you crank the engine.

One thing we always tell people: when an old impeller loses a vane, go find it. Those rubber pieces travel downstream and can lodge in your heat exchanger or oil cooler and choke off flow. Account for every vane. If one's missing, track it down before you button things up. While you're in there, run a finger around the housing and the wear plate and check the cam for scoring. A chewed-up housing will eat a fresh impeller in short order.

This is sold as a single impeller for the F5 pump. If your job calls for the full service parts, the cam, wear plate, end cover, and gaskets are separate items, so check what your pump needs before you tear it down. For a routine seasonal refresh, though, a fresh neoprene impeller is usually all it takes to get your cooling back to full song. Do yourself a favor and carry a spare too. It's small, it's cheap, and it's the single most likely thing to leave you idling at the ramp on a hot afternoon.