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Bukh DV24 cooling system


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Hi all, first post here after many previous visits! 

 

I have a skin tank cooled Bukh DV24, which has a header tank as above. 

 

The hose on the right is cold water from the skin tank. The hose on the left runs down to the water pump. The narrower hose at the top is the return hose from the thermostat housing. 

 

My question is - to my mind, the coolant level (when cold) in the header tank HAS to be above the level of the two lower hoses, or the coolant will not circulate. 

 

Or - if the coolant level when cold is lower than those two hoses - will it eventually expand enough to go above that level, and then start circulating? If so, until that point is the water pump running dry?! 

 

I would really love to understand this properly! Having read previous posts, possibly @Tony Brooks do you think you could advise? I think you might have Bukh knowledge? 

 

I ask because I had been needing to top up the coolant level to various degrees after almost every run.

 

Edited by Chris Watkeys
Clarification
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I have read about coolant 'finding its own level' as it will blow out if overfilled. 

 

However when the engine has returned to cold after a long run, the level in the header tank is often below the two hoses. 

 

On a related note, as I was previously concerned about coolant loss, I have had both a pressure test and a CO test done and both were fine. 

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Remember T W Marine at High Peak are the canal boat Bukh  experts.

 

I think that you are almost there by your comment about expanding coolant. I also think that the expanding coolant is why you are constantly feeling the need to top up. As it expands, it gets blown out of the little overflow pipe into the bilge.

 

I do not think Bukh made a skin tank cooled engine, so yours is probably a conversion for a keel cooled one or a heat exchanger one. In both cases the coolant capacity would be far lower than that for a skin tank, so the greater volume causes more expansion.

 

I would like to know what type of water pump you have and if there are two pumps. It would be good to have an overall view of the engine, pump(s) and pipework so better advice can be given.

 

Take the pressure cap off and see if it has a rubber seal on the underside of the top. If not, take it to a motor factors (car parts place) and ask them for one of the same pressure but with a rubber seal under the cap. Then run a small hose from that little overflow pipe and into the bottom of a container sitting at a similar or slightly lower height. Then the expanding coolant will be blown into the container, and then, as it cools, sucked back in.

 

 

 

Edited by Tony Brooks
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Hi Tony, 

 

Thanks very much indeed for taking the time to reply. 

 

The single water pump is driven off the alternator belt. 

 

I've previously replaced the pressure cap for new and the seal is in good condition. 

 

I'm actually moving the boat at the moment but will add the photos you've asked for this evening when I moor up. 

 

Great idea re: adding a small overflow container - will try and fashion that! 

 

As it happens I will be at Furness Vale in a couple of days so will drop in on TW Marine - thanks for the suggestion. 

 

Thanks again for replying - it's much appreciated - and I'll add those extra photos later.  👍

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1 minute ago, Chris Watkeys said:

Hi Tony, 

 

Thanks very much indeed for taking the time to reply. 

 

The single water pump is driven off the alternator belt. 

 

I've previously replaced the pressure cap for new and the seal is in good condition. 

 

I'm actually moving the boat at the moment but will add the photos you've asked for this evening when I moor up. 

 

Great idea re: adding a small overflow container - will try and fashion that! 

 

As it happens I will be at Furness Vale in a couple of days so will drop in on TW Marine - thanks for the suggestion. 

 

Thanks again for replying - it's much appreciated - and I'll add those extra photos later.  👍

 

To be clear, all pressure caps have one rubber seal on them on the bottom of the hanging down springy bit that seal at the base of the filler neck. I am talking about an extra seal under the silver top of the cap - the silver part, so it seals onto the top of the filler neck. Most pressure caps just have a brass diaphragm at that point, and it is unlikely to form an airtight seal, so rubber is needed there.

 

As far as the container is concerned, I would just hang a plastic milk "bottle" from that convenient bit of angle iron you can see in the photo, so you can see if it works.

To answer the question about the water pump running dry. If it is driven by the alternator belt, then it is most likely to be a centrifugal pump with a metal or plastic centrifugal impeller. There are no rubber wings that can get damaged and its bearings are likely to be sealed and pre-lubricated, so it will run dry perfectly happily.

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After more thought:

 

The water pump is almost certainly lower than the header tank, so even with an empty header tank, the water pump will still be full of coolant. The way the hose to the skin tank runs shows the skin tank is also probably lower than the header tank and so is also full of coolant. As soon as the pump starts, water will circulate through the engine via whatever bypass system the DV20 uses, because the engine is also below the header tank.

 

As the thermostat opens water will be moved from the engine into the skin tank, but as that is full of water, some of the water in the skin tank will be displaced into the outlet hose and thus the header tank.

 

The correct way to assess the correct header tank level is to fill to the brim just once, then go for a cruise. Once the engine has cooled down, so the coolant has contracted, whatever the level in the header tank and/or pipes is, that is the correct level to top up to. If you fill it any more, it will only expel the excess coolant.

 

My guess is that if you take the filler cap off, start and rev the engine while looking into the harder tank you will see that coolant does pass through, across the bottom of the tank until the coolant has expanded. You may also see a stream or drips of coolant from the vent hose that runs from the thermostat housing.

 

 

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Thanks so much for adding that Tony. Your first paragraph there explains what I've been scratching my head over for weeks! Am very glad to finally understand it properly. The crucial gap in my knowledge was the bypass system you mentioned. 

 

I'll do exactly as you suggest and fill to the brim, go for a cruise, then check the level and leave it there.

 

Finally I can stop fretting about non-existent coolant loss!

 

Your advice is really very appreciated, maybe I'll get to buy you a beer some time 👍

 

Cheers and all the best, 

 

Chris 

 

 

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11 minutes ago, Chris Watkeys said:

Thanks so much for adding that Tony. Your first paragraph there explains what I've been scratching my head over for weeks! Am very glad to finally understand it properly. The crucial gap in my knowledge was the bypass system you mentioned. 

 

I'll do exactly as you suggest and fill to the brim, go for a cruise, then check the level and leave it there.

 

Finally I can stop fretting about non-existent coolant loss!

 

Your advice is really very appreciated, maybe I'll get to buy you a beer some time 👍

 

Cheers and all the best, 

 

Chris 

 

 

 

Most modern engines need to keep coolant circulating through the engine when the thermostat is closed. To allow that, the simplest method is to have a small drilling between the cylinder head water jacket and the water pump inlet. Think bypass hose on the original Mini engines. It can be more complex with a "special" thermostat that not only opens the path through the skin tank, but at the same time closes the bypass port. You don't need to worry about any of that unless you are modifying the cooling system. In any case, the calorifier coil circuit also acts as a bypass circuit to maintain flow through the engine as it warms up.

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And don't forget to make sure you have no air trapped in the skin tank, there should be a bleed point at the highest point.

Not all boat builders build a tank with the take off point that can't trap air. 

Air  trapped in the skin tank can cause havoc with water  levels in the engine / header tank.

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Great stuff, thanks JR - will likely drop in in any case 👍

 

On an unrelated note my boat was built in 1980 by a long gone company called Coles Morton, based at Whaley Bridge, so I might see if there are any traces of that also while I'm on the Peak Forest. 

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Thanks Tony! The engine is a recon that went in four years ago, while the engine bilge was empty I took the opportunity to take it back to the steel and repaint. Bit patchy now but mainly ok! 

The original engine was a DV10 which served me well for four years before it started overheating, after the pump was sorted the flywheel didn't go back on properly and it threw it, leaving sheared bolts in the crank shaft. Five out of six bolts we drilled out but the last one just wouldn't come so it was RIP DV10 and in with the recon DV24 

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My engine has a very small header tank similar to yours and runs almost empty. I tried a recovery milk bottle which worked much of the time but every now and then would fail to suck the water back on.  I gave up on the recovery milk bottle in the end ( I did think of fitting it higher than the engine). I think I just worry too much as I’ve never had any problems and assume that as long as the minimum  water level is higher than the pump, skin tank and engine all seems fine as Tony says

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3 hours ago, Chris Watkeys said:

Great stuff, thanks JR - will likely drop in in any case 👍

 

On an unrelated note my boat was built in 1980 by a long gone company called Coles Morton, based at Whaley Bridge, so I might see if there are any traces of that also while I'm on the Peak Forest. 

Didn't they build @J R ALSOP boat Comet and I believe he came from near that area

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44 minutes ago, Peugeot 106 said:

My engine has a very small header tank similar to yours and runs almost empty. I tried a recovery milk bottle which worked much of the time but every now and then would fail to suck the water back on.  I gave up on the recovery milk bottle in the end ( I did think of fitting it higher than the engine). I think I just worry too much as I’ve never had any problems and assume that as long as the minimum  water level is higher than the pump, skin tank and engine all seems fine as Tony says

 

Thanks for posting - good to hear from someone in the same situation and good to know it's not just me that worries too much! 

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9 hours ago, Peugeot 106 said:

My engine has a very small header tank similar to yours and runs almost empty. I tried a recovery milk bottle which worked much of the time but every now and then would fail to suck the water back on.  I gave up on the recovery milk bottle in the end ( I did think of fitting it higher than the engine). I think I just worry too much as I’ve never had any problems and assume that as long as the minimum  water level is higher than the pump, skin tank and engine all seems fine as Tony says

 

I would like to know if you changed your filler cap for one with the rubber seal under the lid, or did you use the original one with the metal diaphragm?

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it looks as if it has the rubber seal, so if the filler neck where it seats is not  distorted an expansion vessel should work reliably unless there is a very soft hose in the system that easily collapses.

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3 minutes ago, Chris Watkeys said:

Ah I see - understood. 

 

With regard to that, am I right in thinking that the hose and the vessel itself will need to be airtight, in order for the coolant to be sucked back in when the engine cools back down? 

 

The red Bukh header tank that you have will have to be airtight, so the contracting coolant sucks on the overflow stub on the filler neck. The new expansion vessel (like a plastic milk carton etc) must not be airtight so air can flow into it as any coolant is sucked back into the Bukh tank.

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14 hours ago, Chris Watkeys said:

Great stuff, thanks JR - will likely drop in in any case 👍

 

On an unrelated note my boat was built in 1980 by a long gone company called Coles Morton, based at Whaley Bridge, so I might see if there are any traces of that also while I'm on the Peak Forest. 

I worked at Coles Morton Marine from about 1970 to 1979 when I left, I built my boat "Comet" with the help of Barry Alger who built shells for Coles Morton who went on to build there own kits shells. 

My Bukh 2G 105 is running well after 45 years faultless service, started life as raw water cooled but I changed to recirculating system as i got fed up of pulling crayfish out of the strainer.

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