Double Impeller Failure

[robyonfrome]

I recently changed both impellers on my Volvo 41b. First trip out both engines overheated, put the old ones back in and no problem, can anyone tell my why please. The new ones were proper Volvo make.

 

[sarabande]

lobes the wrong way round ?

 

[volvopaul]

Simple, your pump bodies are worn out, the old impellers have over the years bedded in to the shape mainly the front and rear faces, when you fit new they need running in, but as you have released the water from the system you need to prime the system to make it pull water again, a good pump will vacuum quite easy and pull raw water straight away, shaft drive boats tend to pull water up easier than sterndrive models for some reason, you also have more exhaust back pressure on a sterndrive install, when you start the engine and the raw water pipes are empty exhaust gas backpressures the system against the suction of the pump, next time try greasing the impellers to give a beter seal so they can suck quicker, also take the strainer lid off and pour some water down there before you start up, I always unscrew the strainer lid straight after a start on a service to release the ex gas and allow water to flow.

Hope that explains a bit.

 

[sarabande]

I was going to add all that as well.......

 

[robyonfrome]

Thanks Paul that makes a lot of sense, I will put new impellers in and new front plates and prime.

 

[Thepipdoc]

I was going to add all that as well.......

LOL!