Volvo Penta MD 2020 D. - Shredding Impellers

[Fairweather Sailor]

Changed our impeller as part of annual service in April 2022, engineer reported just in time with the impeller. Decided to check the impeller in October - 4 blades missing, tracked them down at the entrance to the heat exchanger, replaced with a new impeller (Volvo part), plenty of glycerine applied.
Boat has not been outside the marina since October, but engine started each week. Decided to check the impeller again yesterday. One blade missing and a second about to shear. Can anyone suggest what the problem might be. Water is been expelled normally through exhaust, we always check on starting the engine. thank you.

 

[Fairweather Sailor]

Yesterdays Pic of impeller.

 

[Plum]

Yesterdays Pic of impeller.

Oh dear, very frustrating . Obviously not running dry or even lack of initial lubrication as that would result in wear of all of the blade lobes even if individual blades start to fracrure. Your unbroken blade lobes look in good condition. I had an individual blade break after only 50 hours and as the blade lobes showed no wear ASAP Supplies exchanged the impeller without quibble when I sent them a photo (Orbitrade brand not Volvo branded) as I believe it was due to faulty material or moulding process. Could your two impellers be from the same batch? If so this too could be faulty material.

Www.solocoastalsailing.co.uk

 

[Fairweather Sailor]

Thanks for the response, fairly sure not from the same batch, I purchased from main Volvo supplier in October!!

 

[VicS]

Thanks for the response, fairly sure not from the same batch, I purchased from main Volvo supplier in October!!

I suspect the trouble is caused by the way in which one of the vanes is being doubled back on itself if this is occurring every time the engine is stopped.


Presumably the engine does a small fraction of a turn backwards as it stops. No idea what you can do about it though

 

[PetiteFleur]

You'll probably always get a vane bent when the engine is stopped, as inevitable a vane will stop on the raised portion. It's a genuine volvo item so should be ok. Perhaps complain to Volvo? I've had similar problems with impellers only lasting a few hours - a few years ago approaching a marina in Holland and the engine alarm went off, dropped anchor rapidly and when examined there was only one vane left! Fortunately I had a spare, fitted and ok. I did buy another when we got moored up. I always remove the impeller over winter which gives me an opportunity to inspect. I now have two spare with a single vane missing which are now emergency impellers. Another vane looks as if it's about to fracture....

 

[VicS]

You'll probably always get a vane bent when the engine is stopped, as inevitable a vane will stop on the raised portion. It's a genuine volvo item so should be ok. Perhaps complain to Volvo? I've had similar problems with impellers only lasting a few hours - a few years ago approaching a marina in Holland and the engine alarm went off, dropped anchor rapidly and when examined there was only one vane left! Fortunately I had a spare, fitted and ok. I did buy another when we got moored up. I always remove the impeller over winter which gives me an opportunity to inspect. I now have two spare with a single vane missing which are now emergency impellers. Another vane looks as if it's about to fracture....

but why is it bent over in the opposite direction to what you would expect ?

 

[jwfrary]

More likely the pump is over stressed either by increased back pressure via a blocked heat exchanger or increased vaccum blocked strainer, clogged intake screen, sometime growth sometimes a build up of antifouling. Worth checking the intake hoses aren't collapsing too. Also check the strainer lids not admitting air, nor mounted too high.

Never had an issue with genuine Impellers, my yanmar ones been in for two years! - I check it regularly but can't see the point of chucking something that's fine.

 

[jamie N]

Ever thought about replacing it with an electric impeller? By pass the mechanical item and replace it with something that Toyota use?
About £25.00 on the web, and engineered to last 30,000 hrs.

 

[penfold]

Poor quality rubber; there does seem to have been a lot of this recently even with OE/brandname impellors.

but why is it bent over in the opposite direction to what you would expect ?

Likely the engine rocked backward to release compression when stopped.

 

[Daydream believer]

When my MD2020 was new I had 4 impellers go in the first year. No idea why. I now carry one just inside the engine bay ready for immediate use. I have also changed the cover screws for stainless steel socket screws. This makes it easier to remove the cover fast without losing the screws as they stay on the allen key. ( I have a screwdriver type also in the engine bay)
Since then (20 years) I have only had two go mid season. I do put new ones in every year. I have also found that non volvo ones do not always fit properly, so I avoid them. I carry 5 spare ones.
They could be rubbing on the cover. Mine scored the cover so much that I once could not get the water to pull through. If you think it is put in an extra gasket, I solved the scoring by turning the cover round the other way until I made a new cover. I do not use the paper gasket I use blue gel stuff from a tube. I put 3 pieces of cable tie around the rim. Apply the compound & screw the cover in place. Leave the compound to go rubbery then remove the cable ties & tighten down the cover on the compound. I found the paper gaskets prone to leaking.

 

[Beneteau381]

I suspect the trouble is caused by the way in which one of the vanes is being doubled back on itself if this is occurring every time the engine is stopped.

View attachment 149698
Presumably the engine does a small fraction of a turn backwards as it stops. No idea what you can do about it though

Take the pump off the engine and turn the gear a few degs? Then refit. It will put the blades in a different position from where the engine stops? Unless Perkins put some odd teeth on one of the gears to prevent this a la Triumph twin cylinder engine gear timings?

 

[38mess]

but why is it bent over in the opposite direction to what you would expect ?

Did the op take it out to check and just put it back in that way? That's the only reason I can think why that vane is bent backwards

 

[Plum]

Did the op take it out to check and just put it back in that way? That's the only reason I can think why that vane is bent backwards

It is not uncommon for blades to be bent backwards. As a few previous posters have said already, as the engine comes to a stop it will often kick back in the opposite direction of rotation, enough to bend back any blade that is on the cam. They bend back correctly the next time the engine starts, happens often with no ill effect.

Www.solocoastalsailing.co.uk

 

[vyv_cox]

I think the doubled over vane is probably normal behaviour. There is a video on my website showing that rubber vane pumps reverse themselves readily without any problem.
However, I wonder if the cam is correctly located/damaged/the right one. It looks a bit severe in the photos.

 

[Rappey]

Could it be that your using the wrong type of impellor. They are made from various different materials such as natural rubber, epdm, neoprene, nitrile, silicon.

 

[Spirit (of Glenans)]

Ever thought about replacing it with an electric impeller? By pass the mechanical item and replace it with something that Toyota use?
About £25.00 on the web, and engineered to last 30,000 hrs.

A very clever little pump.
It prompts two questions in my mind:
1. Is it possible to pump in too much water for the exhaust pressure to eject?
2. Many pumps have solid vanes, like this one , washing machines and C/H circulation pumps. Why do the pumps on marine engines need flexible vanes?

 

[VicS]

A very clever little pump.
It prompts two questions in my mind:
1. Is it possible to pump in too much water for the exhaust pressure to eject?
2. Many pumps have solid vanes, like this one , washing machines and C/H circulation pumps. Why do the pumps on marine engines need flexible vanes?

I imagine because they need to be self priming

.

 

[vyv_cox]

A very clever little pump.
It prompts two questions in my mind:
1. Is it possible to pump in too much water for the exhaust pressure to eject?
2. Many pumps have solid vanes, like this one , washing machines and C/H circulation pumps. Why do the pumps on marine engines need flexible vanes?

Exhaust pressure will always eject water in the exhaust but engines have been wrecked by pumping in excess water when the engine failed to start.
These pumps are positive displacement types, needed as VicS says to self prime. The pumps you mention, and the circulating pump in the engine, are centrifugal types that do not self prime.

 

[doug748]

Changed our impeller as part of annual service in April 2022, engineer reported just in time with the impeller. Decided to check the impeller in October - 4 blades missing, tracked them down at the entrance to the heat exchanger, replaced with a new impeller (Volvo part), plenty of glycerine applied.
Boat has not been outside the marina since October, but engine started each week. Decided to check the impeller again yesterday. One blade missing and a second about to shear. Can anyone suggest what the problem might be. Water is been expelled normally through exhaust, we always check on starting the engine. thank you.

I had impellers broken every year with my Johnson pump using genuine Johnson spares (which I believe are Nitrile). I changed to Jabsco replacements and they last several seasons. I understand they are Neoprene - they feel far more flexible in the hand.

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