Johnson Pump 812BT-1 F6 MC97 Flexible Impeller, Bulk Pack of 20

These are the genuine Johnson Pump F6 flexible impellers, sold in a bulk pack of 20. If you run an F6-series Johnson pump for raw-water engine cooling, washdown, or general transfer, this is the wear part that keeps water moving. The impeller is the heart of the pump. When it's healthy you get steady flow and stable pressure. When it's worn, you get overheating, weak washdown, and a bad afternoon.

Each impeller is molded from the MC97 compound, the flexible nitrile material Johnson Pump uses for its marine raw-water impellers. The vanes flex as the shaft turns and sweep water through the pump housing. That flexing is exactly why the impeller is a wear item. Over a season the vanes take a set, the tips wear, and eventually one cracks or tears. Run the pump dry even for a short stretch and you can cook an impeller in seconds, because the water is what keeps those vanes cool and lubricated. So the smart move is to keep spares on hand and change them before they fail, not after.

The bulk pack of 20 is built for people who go through impellers. Repair shops, boatyards, engine rebuilders, charter fleets, and anyone maintaining a row of boats with F6 pumps. Buying the 20-pack drops your cost per impeller well below the single-unit price and means you're never waiting on a part when a customer's boat is on the lift. If you only need one impeller for a single seasonal service, this probably isn't the pack for you. But if you keep a parts drawer stocked, it pays for itself fast.

Fitment is straightforward. These are the F6 impeller with the splined bore drive, measuring 2-1/4 inches (57.1 mm) across the outer diameter and 1.9 inches (48.2 mm) wide. The splines slide onto the pump shaft so the impeller is driven positively without a key or setscrew. Before you order in volume, pull one of your worn impellers and confirm the outer diameter and width match. F6 housings are specific, and an impeller that's even slightly off on the OD won't seal against the cam the way it should.

Changing one is a ten-minute job once you've done a couple. Pull the pump cover, work the old impeller off the shaft, coat the new one in a little glycerin or dish soap so the vanes seat without dry drag on first start, and slide it home. A lot of techs bend the vanes the same direction the pump turns as they push it in. Because these come bulk with no cover gasket or o-ring in the pack, keep a few gaskets in your kit if your service calls for a fresh one. And do yourself a favor, change the impeller on schedule. Most raw-water impellers get swapped at least once a season or on the engine maker's hour interval, and with 20 in the box you've got no excuse to run one past its life.

How do you know it's time? Pull the cover and look at the vanes. Cracks at the base, torn or missing tips, a permanent curl or flat spot where the vanes have taken a set, or a gummy, swollen feel to the rubber all mean that impeller is done. Any black rubber flakes downstream in the cooling circuit are a sign an impeller already came apart, and you'll want to chase those bits out of the system so they don't block a hose or a heat exchanger. Water quality matters too. Silty, sandy, or fuel-contaminated water is hard on the rubber and shortens impeller life, so boats working dirty water go through these faster than a clean-water cruiser.

For off-season storage, some owners pull the impeller entirely and store it in a bag so the vanes don't take a permanent set sitting bent in a dry housing all winter. Others leave it in and just replace it at spring commissioning. Either way, having a stack of 20 on the shelf makes that call easy. Keep them out of direct sunlight and away from heat, and they'll wait for you in the drawer for years.