This year we checked the first time our impeller. Better late then never. One should check it every season just to make sure it is in a good shape. Any damage to it might compromise the cooling and that can lead to overheating of the engine which should be avoided.
First was to check where the impeller is on our Volvo Penta MD5. It is at the back of the engine so long arms are helpful. The impeller is behind the brown round cover. The two hoses carry the water.
The cover is fixed with four screws and when removing it one finds the impeller right there.
In order to push the water forward one part of the round frame is a bit thicker in order to bend the blades of the impeller to create enough pressure to push the water forward.
The impeller is attached to a shaft that can be removed from the pump housing. The impeller sits quite tight in the pump and is easiest removed with needle-nose pliers.
The impeller is fixed to the shaft with a screw and by removing the screw one can remove the impeller.
Our impeller looked still very good. It was flexible enough and did not have any cracks or holes so we put it back in. The end of the shaft that goes into the pump house has a wide slit. That is where the rotator in the pump connects with the shaft. If the shaft is not in the right position the impeller does not fit completely to the pump case and cannot be shut. With a bit of turning it is easy to get the shaft into the right position.