Bukh - no cooling water

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rex_seadog

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On our last sail when we came to start our engine (Bukh DV20, sea water cooling) prior to dropping sails and entering harbour we found we were getting no cooling water from the exhaust and the overheating alarm sounded. Luckily we were able to moor up with minimal help from the engine. When tied up we checked the inlet strainer (OK) and replaced the apparently good and fairly new impeller and started the engine - no problem, good water flow. The next day, after a good sail, the same problem, but this time we were faced with entering the Dart against the ebb and with a head wind. We were making some progress but eventually managed to secure a tow to get us in before closing time! Next day we checked the thermostat, exhaust elbow (had massive blockage here some years ago) - all appeared OK and again from rest the engine started up with plenty of cooling water and got us up river to our permanent mooring.
Then spoke to the guys at Bukh who suggested that it was probably due to a worn pump (engine dates from 1984) so we duly removed it and have since returned it to Bukh for overhaul. They replaced various bushes and seals (excellent 3 day turnaround) but didn't find much wear to the body of the pump. We have yet to return to the boat and refit the pump but I'm still concerned that we might not have cured the problem. We haven't yet removed the T piece to check for any restriction (but poking down with a piece of wire didn't locate any apparent blockage) and once water is flowing everything is fine and we get a good healthy flow all the time i.e whether thermostat open or not, so a blockage in the system seems unlikely
It seems that when the boat is moving along under sail (even when reasonably upright) we are having the problem - from my physics of many years ago I guess this is due to the venturi effect making it harder for the pump to prime. It is only recently that this has occured so any thoughts would be welcome in case we have to investigate further.
 
rex_seadog said:
On our last sail when we came to start our engine (Bukh DV20, sea water cooling) prior to dropping sails and entering harbour we found we were getting no cooling water from the exhaust and the overheating alarm sounded. Luckily we were able to moor up with minimal help from the engine. When tied up we checked the inlet strainer (OK) and replaced the apparently good and fairly new impeller and started the engine - no problem, good water flow. The next day, after a good sail, the same problem, but this time we were faced with entering the Dart against the ebb and with a head wind. We were making some progress but eventually managed to secure a tow to get us in before closing time! Next day we checked the thermostat, exhaust elbow (had massive blockage here some years ago) - all appeared OK and again from rest the engine started up with plenty of cooling water and got us up river to our permanent mooring.
Then spoke to the guys at Bukh who suggested that it was probably due to a worn pump (engine dates from 1984) so we duly removed it and have since returned it to Bukh for overhaul. They replaced various bushes and seals (excellent 3 day turnaround) but didn't find much wear to the body of the pump. We have yet to return to the boat and refit the pump but I'm still concerned that we might not have cured the problem. We haven't yet removed the T piece to check for any restriction (but poking down with a piece of wire didn't locate any apparent blockage) and once water is flowing everything is fine and we get a good healthy flow all the time i.e whether thermostat open or not, so a blockage in the system seems unlikely
It seems that when the boat is moving along under sail (even when reasonably upright) we are having the problem - from my physics of many years ago I guess this is due to the venturi effect making it harder for the pump to prime. It is only recently that this has occured so any thoughts would be welcome in case we have to investigate further.
Click to expand...

A boat in our marina had this problem recently. The cover was worn so a pal made a new cover out of scrap brass and now works fine. Maybe your pump now has a new cover?
 
Water flow from the exhaust is not always a good guide as most of what you are seeing is bypass water. A good guide is to hold the palm of your hand on the cylinder head - you should just be able to keep it there for several seconds. If not, it's overheating. Perhaps the most common cause of this is that the water injector into the engine (the gas poker) is blocked by deposits. It is bolted to the block behind the flywheel and can be withdrawn with a bit of ingenuity, best with a ball-ended allen key.

Otherwise, failure of the pump to prime after sailing is not uncommon. A good way to overcome it is with a Vetus strainer, mounted 15 cm above the water line as recommended. It is easy to prime this to get the pump going again, I keep a bottle of seawater in the bilge for this purpose. Check all the fittings on the upstream side of the pump for air tightness but this may not solve the problem. Get used to listening for the engine exhaust note when you start, it becomes easy to recognise whether coolant is present or not.
 
Hi Bilgediver - just checked - original cover and not machined- just cleaned up. Had quite a chat with guys at Bukh and although there was a slight scoring at the back just above the cam they didn't consider this warranted any attention.
 
Hi Vyv - thanks for that.

Yes, removing the T piece is next on the agenda as it is some time since this was checked. As you say, this can be done without removing the flywheel with some ingenuity and, I would add, a lot of swearing! I suppose that the engine can be running fairly hot due to restricted cooling before the alarm starts to sound. Maybe not a bad thing normally as I understand direct cooled Bukhs tend to run on the cold side. Just a thought, if the thermostat was still in the open position (i.e. diverting water through the block) and the poker was partly blocked perhaps this could make priming more difficult. However, we had been sailing a couple of hours without the engine each time so surely the engine would have cooled suficiently by then.

Will have to consider the Vetus strainer but I don't recall ever having the priming problem before. As you say, the exhaust note is quite different (hollow) when no water is flowing.
 
Not entirely sure if you are getting significant water flow from the tell tale, when the overheat alarm is sounding. If you are, then it may be the sender itself, which is mounted in the top of the manifold. We had intermittent heat alarms over the early part of this season, but tell tale flow, intake & impeller all OK, so eventually replaced the sender with a new unit from Furneaux Riddall. Not cheap , but 20% less than Bukh price & end of problem. For info, the sender is this one at the top:

http://www.furneauxriddall.com/acatalog/VDO_Temp_Sender_Earth_Return_with_W_C.html

If it is actually overheating through blockages, you could try cycling a Fernox , Rydlyme or similar solution throught the cooling system to help clean it out.
 
I know you'll already have gone through this process, but some of the comments so far seem a little illogical. I notice you said no water in the exhaust (not a telltale) so if there's no water coming out of the exhaust then there is no water circulating in the engine - period. Obviously you should check the whole external path for kinked hoses or blockages, but ultimately the times it fails is when you have been sailing. It seems likely that you are losing the water from the pump's feed hose and then failing to re-prime. With a pump in good condition, it will effectively work as a non-return valve holding water in the supply pipe and should have no need to prime again. As I understand it, the most common failure of an impellor pump to work is for the end plate to become worn, so that it no longer forms a sealed chamber and the pressures equalise either side of the vanes. That is why a new cover and impellor often solves the problem. People have also reported that the pump fails to prime after sailing on one particular tack.

Until you really get to the bottom of it, you might find that closing the seacock immediately you stop the engine will hold sufficient head of water to re-prime by stopping it from dribbling out. By the way, check that the seacock is opening and closing as required! Easy enough if you dettach the hose and turn it on and off - and you'll have clean bilges after you've mopped it all up. If you have to replace the cover, you might consider the upgrade to the latest SpeedSeal - it features QD fitting by knurled thumbwheels, an o-ring seal and flat PTFE seal against the impellor to prevent further wear of the brass.

Rob.
 
The OP has had the pump rebuilt by Bukh, so presumably there is no problem with the end plate.

I have gone through all this myself, replacing the end plate, closing the valve when sailing, adding a NRV, but the problem still occurs. It just seems to be easier and cheaper to reprime when necessary than go through a major replacement exercise.
 
Make sure that the top bit of the thermostat assembly is pointing in the right direction. It fits both ways round but wiil only let the water go in one direction. How do I know this? :o
 
vyv_cox said:
The OP has had the pump rebuilt by Bukh, so presumably there is no problem with the end plate.
Click to expand...

I know I'm a cynic and would hope that Bukh would have tested the rebuilt pump, but the number of times I've had a garage repair my car and then refuse to accept that there is still a problem... Sometimes just have to fix it yourself.

The suggestion of the upgrade is my own philosophy - even if it doesn't cure the problem, you've still got the upgrade you paid for (and a spare cover).

Rob.
 
Take hose off water intake sea cock and prove water passes through sea cock.
Is the outside grill on the through hull fitting completely clear?
Is there air getting in from a connection on or below the pump.
Is the pump face sealing?
Can the thermostat stick shut when hot? Can you try running it with thermostat out?
Is the impeller housing letting in air when engine hot?
If the water is getting past the pump where is it going? in the bilge? into the engine sump? I guess not you would have spotted that already.. Engine oil isn't creamy white is it?
If it occurs again can you take off a hose, engine side of pump, to see if water is getting that far?
good luck.
S.
Bukh owner..
 
rex_seadog said:
On our last sail when we came to start our engine (Bukh DV20, sea water cooling) prior to dropping sails and entering harbour we found we were getting no cooling water from the exhaust and the overheating alarm sounded. Luckily we were able to moor up with minimal help from the engine. When tied up we checked the inlet strainer (OK) and replaced the apparently good and fairly new impeller and started the engine - no problem, good water flow. The next day, after a good sail, the same problem, but this time we were faced with entering the Dart against the ebb and with a head wind. We were making some progress but eventually managed to secure a tow to get us in before closing time! Next day we checked the thermostat, exhaust elbow (had massive blockage here some years ago) - all appeared OK and again from rest the engine started up with plenty of cooling water and got us up river to our permanent mooring.
Then spoke to the guys at Bukh who suggested that it was probably due to a worn pump (engine dates from 1984) so we duly removed it and have since returned it to Bukh for overhaul. They replaced various bushes and seals (excellent 3 day turnaround) but didn't find much wear to the body of the pump. We have yet to return to the boat and refit the pump but I'm still concerned that we might not have cured the problem. We haven't yet removed the T piece to check for any restriction (but poking down with a piece of wire didn't locate any apparent blockage) and once water is flowing everything is fine and we get a good healthy flow all the time i.e whether thermostat open or not, so a blockage in the system seems unlikely
It seems that when the boat is moving along under sail (even when reasonably upright) we are having the problem - from my physics of many years ago I guess this is due to the venturi effect making it harder for the pump to prime. It is only recently that this has occured so any thoughts would be welcome in case we have to investigate further.
Click to expand...



By inlet strainer do you mean black plastic type. ?? Check the rubber seal under the lid I had one fail, which meant that the pump failed to prime because of air lock and so no water .
 
I don't know whether you ever resolved this problem but I have experienced the same cooling problem on my Bukh 10 recently. I checked all hoses, changed the pump impeller, cleaned the engine waterways with acid, replaced the thermostat, and checked that the water injector to the exhaust was clear and to help monitor the temperature I also fitted a temperature gauge. The engine produces a good flow of water when first started and the thermostat is working correctly adjusting as I apply more power. If I stop the engine and restart it within a short period there is no problem but if I sail for a couple of hours I find that there is no seawater at the water pump (I think this could be caused either by the water syphoning back down the line to the sea inlet which I think is the likely cause or its forced there by gas pressure from the exhaust; unlikely) and hence when I come to restart the engine the pump is unable to pump water through the engine. I also noted that when I check the strainer at the sea inlet it either contains warm water that has passed back down the system or its dry. (Oh and yes I have checked the strainer and blown through but this makes no difference) I am wondering if its possible that water passing the sea inlet at speed when sailing is sucking the seawater back down the line, acting in a similar manner to a self bailer system. My thoughts are to fit a non-return valve in the water pump line, fit a bleed system to the line or to shut the sea cock when sailing which is my least favourite solution as one day I'm bound to forget to check that its open. Any thoughts on the above appreciated.
 
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