Bukh DV20 water pump problem

[Malish]

I think you will find that the entry into the engine is blocked by salts. The nozzle is partly hidden behind the flywheel, held on by two Allen bolts but can be removed without taking off the flywheel. The back pressure generated by this has caused the pump to try to deliver higher than design pressure, hence the characteristic damage. A less likely alternative is that the thermostat could be stuck open, which blocks the bypass, although water will still flow through the engine passages.

One to add: I had a cooling problem with my DV24 - it was salts in the engine feed pipe but they were not easily visible, they were just beyond the right angle bend feeding into the engine - only discovered and cleared//disrupted with a length of monel wire, so even if the pipework looks blockage free, do a little investigation of the blind spots.

And make up a rubber gasket for re-installation of the pipe - seals much better than the original

 

[vyv_cox]

As far as I recall, I just used a standard allen key of whatever size it was (maybe I started the bolt moving with a standard hex, and then shifted it out with a ball-ended one?), and once the bolts were out, just wiggled the pipe by hand to get it to come out. I seem to recall it was rather more trouble to get the more awkwardly placed of the two bolts started to go back in than it was to get it out.

It's a very long time since I owned a Bukh but I think I used a standard Allen key. Easy to cut the end off one if necessary with an angle grinder. They are quite hard for a hacksaw.

 

[vyv_cox]

On a raw-water cooled engine any broken pump vanes will try to go into the engine, assuming the thermostat is open. They will almost certainly not pass through the nozzle into the engine, so as RivalRedwing says, a good rodding through may be necessary.

 

[Boater Sam]

I would clean it out thoroughly, fit a new impeller and put the end plate back on the other way round before splashing out on a new pump.

 

[sgr143]

On a raw-water cooled engine any broken pump vanes will try to go into the engine, assuming the thermostat is open. They will almost certainly not pass through the nozzle into the engine, so as RivalRedwing says, a good rodding through may be necessary.

I've not lost any pump vanes in the 4 years I've had the boat - but in view of trying everything I'll certainly do that! Steve

 

[sgr143]

I would clean it out thoroughly, fit a new impeller and put the end plate back on the other way round before splashing out on a new pump.

If I didn't live so far from the boat, and if I hadn't already lost so much of this season to lockdown, I'd for sure go with that - but as it is, I'll go for the new pump (ASAP had one in stock), and I hope be on my way rejoicing with the minimum of going round loops of trying things to see if they work.

 

[sgr143]

Periodic soaking in hydrochloric acid is the best option, after removing the anode, but cleaning the entry nozzle every couple of years will solve that particular problem.

Update: as Vyv suggested, it was a clogged waterway in the "poker" fitting that was the problem. I hadn't spotted it earlier, as the blockage wasn't in the "poker" bit, but in the pipework that goes up to the thermostat housing. So the the bypass route for water, when the thermostat closes, was not open; hence the high system pressure, and the damage to the water pump. I cleared it out with judicious use of that universal tool, the cu-off wire coat-hanger. Refitting was a bit of a bugger - that lower bolt is nearly, but not quite, impossible to get back in a tighten up, but was done without too much swearing.

Although I had a replacement pump, I couldn't get the old one off. So I cleaned up the old pump body as much as I could, lapped the inner face of the lid fairly flat, and put a new impeller in. Result - more water coming out of the back than I've ever seen before, and no steam. I'll fit a new pump lid next time I'm down, as the lapping couldn't remove all the grooves (I was wearing my finger ends off!).

So I think the engine, which has steamed all the time I've had the boat, has had a progressively blocking-up overflow pipe, which finally went fully blocked. Now added as a periodic winter maintenance job - perhaps every couple of years, check and clean out the engine's exterior water pipework.

Thank you all, but especially Vyv, for the advice.

Steve

 

[Velopaul]

Just have to let you know how grateful I am to this invaluable forum for once again delivering the answer not only to Steve the OP but all the other Bukh owners who, like me, must be mystified by the amount of steam (and lack of water) that issues from their exhaust pipe.
The water pump , raw water inlet, flexible pipes have all been the focus of my attention and servicing /replacing these has improved the flow but reading this thread I know this is the same problem as I have,
I was contemplating changing the engine, it was annoying me so much.
Big thank you sgr143 for posting and vyv_cox for the solution to this, and many other Sadler related issues.