GM30 sea water pump impeller

[Contest1]

I,v just refitted my old Johnson impeller as the new impeller failed to deliver enough pressure to feed cooling water to the engine.
This is the second new impeller, bought from different local marine supliers here in Dublin, that has failed to deliver despite appearing to be identicle to the existing 10 year old one.
The pump face is worn but I can,t see how that adversly effects the newer ones.

 

[Blueboatman]

You might have a partial blockage further down the line( engine) ?

 

[Tranona]

I,v just refitted my old Johnson impeller as the new impeller failed to deliver enough pressure to feed cooling water to the engine.
This is the second new impeller, bought from different local marine supliers here in Dublin, that has failed to deliver despite appearing to be identicle to the existing 10 year old one.
The pump face is worn but I can,t see how that adversly effects the newer ones.

You have answered your own question. The lack of pumping is almost certainly the worn face plate! Replace it - perhaps with a Speedseal.

 

[sailorman]

You have answered your own question. The lack of pumping is almost certainly the worn face plate! Replace it - perhaps with a Speedseal.

and the "wear" plate at the back of the pump too

 

[vyv_cox]

But could also be the cam. See http://coxengineering.sharepoint.com/Pages/Waterpump.aspx 12th photo down. Also, worn shaft seals are a source of air that contributes to priming failure.

It seems unlikely that any impeller correct for the pump could fail to deliver. The problem certainly lies in the pump itself.

 

[Contest1]

Thanks for the responses.
I will probably get one of those quick change face plates, but still wondering why the old impeller, which must have 10 years wear , can pump through the engine while two identical replacements can,t.

 

[sailorman]

Thanks for the responses.
I will probably get one of those quick change face plates, but still wondering why the old impeller, which must have 10 years wear , can pump through the engine while two identical replacements can,t.

while your at it remove the cam & replace the wear plate in the engine end of the pump
ASAP supplies have all the spares

 

[vyv_cox]

Thanks for the responses.
I will probably get one of those quick change face plates, but still wondering why the old impeller, which must have 10 years wear , can pump through the engine while two identical replacements can,t.

Are you certain that the impellers are identical? The width of impellers varies, which may lead to a gap down the sides of the two new ones.

 

[Steve C Cronin]

Unless it is badly pitted, painted or corroded, try flipping the backplate over and fitting it reversed. Note the fine lip seal around the sides of the impellor hub and the individual vanes. They are supposed to seal the sides of the impellor.

 

[Contest1]

Thanks again,
Going to check the width more carefuly when I get the quick release , but doesn,t look like the face plate is reversable as it has the Johnston stamped into it.

 

[Cloven]

I may be wrong but I have had several Yanmar GM series engines and none has had a Johnston pump. It may be that at some time the standard Yanmar pump has been replaced with a Johnston one, hence the reason the Yanmar impeller will not work. If I am wrong then apologies.

 

[pagoda]

Unless it is badly pitted, painted or corroded, try flipping the backplate over and fitting it reversed. Note the fine lip seal around the sides of the impellor hub and the individual vanes. They are supposed to seal the sides of the impellor.

The face plate (covering the impeller) on my 3gm30 pump did have some wear showing. I polished the other face (flat plate anyway) and turned it over, fitted a new impeller at the same time. Flow improved somewhat, so not at the pump replacing stage yet!

 

[sailorman]

Thanks again,
Going to check the width more carefully when I get the quick release , but doesn,t look like the face plate is reversible as it has the Johnston stamped into it.

just polish out any burrs & flip it over, it will last years more