DownWest
Well-Known Member
Think that some had the pump facing aft, so, that, along with the usual lack of forthought to maintainance on most boats, makes impellor changing a challange.
The 1 & 2 GM have them on the front, so easy.
PBO Shredded Impellor article
- Thread starter pyrojames
- Start date
The 1 & 2 GM have them on the front, so easy.
Neeves
Well-Known Member
I don't recall why I should think this but in the hidden recesses of my memory the seawater pump on the Volvo MD engines (our is a MD2020) is a buy in by Volvo from Johnson - so if this can be verified then Johnson impellers should (?) be as good. Our nearest access to Johnson spare parts is 20km and Volvo 3km - so we like you have used Volvo impellers - they might be overpriced but they are not that expensive.
Jonathan
Neeves
Well-Known Member
I suspect not necessarily a bad engine design but a bad installation design or the design not necessarily chosen for ease of servicing - and its a yacht - what would you expect. Most of these engines would, almost, be a joy to service if at waist or chest height with all round access. Ours Volvos, in a cat, are located in a very narrow hull so there is no side access other than lying over the engine, head down, bum up. Really convenient for changing oil filters. We changed our oil filter location to a remote location, with 2 pipes and 2 adaptors for this reason.
You would not think it would be difficult to have all the filters, 1 x seawater, 1 x oil, 2 x fuel + spare CAV fuel) remotely located in a neat line, easily accessible with a matching drip tray (rectangular bucket) underneath.
Jonathan
penfold
Well-Known Member
Of course; VP don't make seawater pumps or impellors any more than Cummins, Caterpillar or Yanmar do, they buy them from Johnson/Jabsco/Sherwood. If you want OE quality buy from the people who make the pumps, although even that isn't straightforward with the counterfeiters turning out convincing branded packaging these days.
Daydream believer
Well-Known Member
The poor impellors i bought were on a chandlers shelf with no packaging, just loose. I bought 3 because they were so much cheaper. They had to be forced on due to poor moulding. The threaded spindle was very slightly off centre causing it to bind. Otherwise looked the same. Once 1 failed I chucked the other 2 to avoid accidentally using them.
roaringgirl
Well-Known Member
We've covered at least 5000 miles over 3 years since I last replaced the impeller on our Yanmar. We must have done a few hundred hours of motoring in that time. I have never seen any hint of failure on our impeller and have only evemtually changed it because it has been in service so long.
I wonder what the difference is between my situation and those who find damage after 50 hours?
I wonder what the difference is between my situation and those who find damage after 50 hours?
Halo
Well-Known Member
So far my impellers have lasted like yours - a long time. It cannot be normal for impellers to need replacement after 50 hours and there is something wrong if bits are coming off to the extent that a strainer is being contemplated
Rather than mitigating the symptoms I would try to find the root cause.
For the impellers to fail the most likely cause is running dry and the most likely cause of running dry is that the raw water system is not sealed. Even a tiny leak in the strainer will allow the water to drain back and cause the pump to have to self prime each time the engine starts. Self priming means running dry and damaging the impeller. A blockage or restriction in the inlet line could also do the same.
Fin d the cause and cure the problem!
dune16
Well-Known Member
I've only had a single impeller failure... marina started the engine (at my request when I was back in UK during lockdown) but didn't check the raw water inlet seacock was open. They noted no water flow and turned it off after a minute or so but the damage was already done. I got to the boat months later and saw the impeller no longer had any fins on it. I was concerned if the debris had clogged thf exchanger but I've since run the engine for 20+ hours with no overheat issues and plenty of water flow. Hopefully I dodged a bigger problem
rib
Well-Known Member
And where do you think the fins have gone ??
dune16
Well-Known Member
I know ? hopefully as the engine only has 160 hours it was all pretty clean and this 1 impeller passed through. Worth getting the heat exchanger taken apart in the winter?
roaringgirl
Well-Known Member
I'd be very surprised if they 'just passed through' the heat exchanger.
Also, it takes a lot more than a 'minute or so' running dry to wreck an impeller.
rib
Well-Known Member
You could look at just the end cap.. Or I have heard a wet vac from impellor hose to h/E has some good results.. Counts the bits and try find the same.. If not it may come and bite you some time ???
michael_w
Well-Known Member
I was told by a couple of sources that it is advisable to change the impeller when departing the Baltic for the North Sea as the impeller was affected by the change in salinity,
penfold
Well-Known Member
They had the presence of mind to check that but didn't check the seacock? The impellor would need to be made of cheese to fail inside a minute, more likely they left it idling then wondered why it was noisy.
dune16
Well-Known Member
Yes, I agree, I wasn't impressed and this was one of a couple of reasons we left that marina as soon as we could get to the boat. Should I be immediately concerned bearing in mind we did alot of motoring last trip over without issue? Ideally it's a job I'd like to save for the winter...
theluckyone17
New Member
Due to a leaking weep hole on my Volvo MD2B's raw water pump, I pulled the entire pump and took it back home to rebuild. The existing impeller looked fine, but I replaced it anyway. Wasn't until I greased and installed the new impeller that I noticed the big chunk of black gunk on the output side. Thinking it was a gob of grease, I grabbed a q-tip and tried to swab it out, discovering it wasn't grease at all. At some point in the pump's past, an impeller had let go, and a chunk of it jammed there. It's very unlikely anyone would have seen the chunk while the pump was installed, due to the angles involved.
zulloboy
Well-Known Member
Changing, or at least checking, the CW pump impeller is a fairly easy and inexpensive task (unless you are unlucky and have a difficult installation). Conversely the consequences of failure on the water can be extremely high.
So it surprises me that it isn't always regarded as an essential part of annual engine servicing. Cooling failure is right up there with flat batteries and gunky diesel for engine failures.
Cheers, Graeme
So it surprises me that it isn't always regarded as an essential part of annual engine servicing. Cooling failure is right up there with flat batteries and gunky diesel for engine failures.
Cheers, Graeme
TSB240
Well-Known Member
Can you quote your sources please?
We are based in a fresh water fed dock and have not found any localised higher incidence of impeller failures.
I can see that an impeller suddenly exposed to a denser medium could cause impeller failure.
More likely if the impeller was in poor shape to begin with.
michael_w
Well-Known Member
The advice came from a chum who's spent his life working on large racing yachts (he reckon's he's sailed 750,000 miles) Corroborated by another BN. The Baltic is the problem apparently.
Tim Good
Well-Known Member
Agreed. I ran my genset dry for only a very short while. Like perhaps 20 seconds and the impeller disintegrated. As you say, if water flow was partially restricted then I imagine this would happen also just not as quickly.