How to Replace a Moomba Mobius LSV Water Pump Impeller

The impeller on an engine moves water up from the lower unit and into the cooling system, which protects your boat’s motor from overheating. 

Replacing the water pump impeller according to the manufacturer’s recommendation is important because the rubber in the impeller can break down, reduce the impeller’s efficiency, and even break apart and clog the cooling system. With that in mind, here’s how to replace the impeller on a Moomba Mobius LSV.

Tools and Supplies - Moomba Mobius Impeller Change

  • 8mm socket
  • Ratchet
  • Flatblade screwdriver
  • Needle-nose or vise-grip pliers

The impeller is located inside the water pump, which is on the front of the engine. On the Moomba Mobius, it faces toward the rear of the boat.

Moomba Mobius LSV Impeller Replacement

Step 1. Remove the four 8mm (or 5/16th) bolts that hold the water pump cover in place to access the impeller. 

Moomba Mobius water pump impeller replacement

Moomba Mobius water pump impeller change

Step 2. Remove the cover and its gasket to inspect the inside of the cover for wear. Look for deep grooves cut in the cover, since that can wear out the impeller. 

Moomba Mobius LSV water pump impeller change

Step 3. Spray silicone spray around the impeller, then turn the engine over a couple of times to rotate the impeller and smear the silicone spray around. This loosens the impeller inside its housing. 

Moomba Mobius LSV water pump impeller replacement

Step 4. Remove the impeller using a pair of pliers by grabbing one of the vanes on the impeller and pulling it out. 

Moomba Mobius impeller change

PRO TIP: If you experience difficulty removing the impeller, lock a pair of vise-grips on one of the impeller vanes, and use a flat-blade screwdriver as a lever to pull the impeller out. 

Moomba Mobius impeller replacement

Step 5. Add some marine-grade assembly lube to the splines in the center of the new impeller

Moomba Mobius impeller how to replace

Step 6. Spread the lubricant that comes with the impeller on the vanes and the inside of the impeller housing to make it easier to install. The lubricant also prevents a dry start-up that could damage the impeller. 

Moomba Mobius LSV impeller change

Step 7. Rotate the impeller as you slide it into place before it engages the splines to get the vanes turning in the right direction.

Moomba Mobius LSV impeller replacement

Step 8. Install the gasket on the impeller housing cover. 

Moomba Mobius LSV water pump impeller housing cover

Step 9. Run the four bolts in hand-tight first, then use a ratchet to tighten them up completely and you’re done. 

Moomba Mobius LSV water pump impeller installation

NOTE: The brass bolts are very soft and can easily strip, so don’t overtighten them.

Replacing the water pump impeller is just one basic maintenance task to keep your Moomba Mobius engine healthy. Changing the oil is another. Watch the video above to see how to change the oil on a Moomba Mobius LSV



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