BUKH DV24. Freshwater conversion

[Sailaway1949]

I have a bought a BUKH DV24 with little hours on it. It is currently raw water cooled and I want to convert to freshwater cooling. Can anyone out there provide any information on what is required and where I could obtain the parts/drawings The engine is currently fitted to a motor boat so space is not an issue.

 

[jamie N]

Welcome to the forum. I'm not familiar with a DV24, but have converted my own RM90 10hp single diesel.
It's simple enough, but involved quite a number of components, which might put some off.
My engine has an internal impeller, in much the same way as most other engines. This is still the case, but the input to the engine comes from the output of the heat exchanger, and then through the engine and out to the input of the heat exchanger. A simple closed loop cooling system of fresh water.
I didn't want to have a mechanical thermostat with seawater flowing through it, so made the system with 2 diaphragm electric pumps, which pump seawater through either the heat exchanger and the exhaust, or just the exhaust, depending on the engine temperature. Which pump is running is dependent on the engine temp, which by way of having a capillary thermostat (as a cooker does) to a relay, switches on the appropriate pump: if the engine needs cooling the seawater is pumped through the heat exchanger, so that once the engine temperature is at the correct 'coolness', the relay switches to the exhaust only pump. With this method the exhaust has a continuous flow of cooling water.
The pumps are manually 'activated' after the engine has started which avoids any issue of flooding the engine, should it have trouble firing up. From this same switch the alternator is also activated; it's a small engine and as such can have problems labouring when initially starting trying to charge the batteries. I've never had an issue with 'forgetting' to activate this switch, as it's part of the starting procedure as much as making sure the seacock is open.
It sounds far more complicated than it really is, and it works well with 'dozens' of hours on it during my curtailed summer of sailing, indeed I see no reason to alter it.
I made it like it is because the option of having a mechanically driven pump would've required a good deal of work adding frame and pulleys to another impeller pump.
Each diaphragm pump is about £20, and the capillary thermostat £15 or so, and readily available.
Redundancy is built in; if a pump goes down, then simply either adjust the thermostat or change to the 'other' pump. If both electric pumps break, then revert to the impeller by rearranging the 2 hoses. If the impeller were to fail, then one can use either of the electric items to cool the engine. All hoses are interchangable.
The engine system is unpressurised, and has a header tank from a Ford Fiesta, through which the thermostat is fitted to control the relays. The heat exchanger for mine is 22kW, and trouble free with standard fittings and widely available.
Nothing here is 'Yottie' stuff, out of preference.
Many might roll their eyes, but other reliable options aren't widely available, and won't cost under £100.
I do have an association with this type of 'machinery' so wasn't unduly threatened by the few relays and piping, which others might rightly prefer to avoid.

 

[oldmanofthehills]

I was briefly owner of a freshwater cooled buhk24. It had a seawater pump and a freshwater pump both driven by the engine and that is what you need. The heat exchanger was bukh and fitted in its conversion from keel cooled ships lifeboat engine. Exchanger is fairly expensive so I was told, but any yacht exchanger would do.

Obviously sea water pump drives sea water through exchanger and out into exhaust. The freshwater pump circulate antifreeze rich water in closed pressurised system with header tank and it is this system that must have the thermostat. Though it is not that hot I dont see how an unpressurised system could work as I understand that the engine pistons in the sump pumps air to give positive pressure in the block to keep out water. Certainly mine spewed out water in pulses if I left the header tank cap off. Maybe a non-ex-lifeboat engine doesnt have that positive internal pressure

 

[AntarcticPilot]

I may be missing a trick, but why bother? Raw water cooling is much simpler, and on an engine like the Bukh, I don't see the advantage. All you're doing is adding complexity and additional points of failure for doubtful advantages. The engine may run slightly hotter, and it may last a little longer. I doubt the second - something else will limit the life of an engine like a Bukh long before internal corrosion kills it.

An awful lot of engine related posts on here are related to problems with heat exchangers, to the extent that I see them as a problem waiting to happen.

 

[penfold]

To answer the OP the parts needed to convert are detailed in Bukh's own parts list available from the Bukh website, although be sitting down if you ask Bukh to quote for a kit of parts. For cost reasons I'd look to substitute a generic Bowman heat exchanger and a fresh water pump from other than Bukh but this is not straightforward.

I may be missing a trick, but why bother? Raw water cooling is much simpler, and on an engine like the Bukh, I don't see the advantage. All you're doing is adding complexity and additional points of failure for doubtful advantages. The engine may run slightly hotter, and it may last a little longer. I doubt the second - something else will limit the life of an engine like a Bukh long before internal corrosion kills it.

Engine warms up quicker, engine runs hotter and more efficiently, makes hotter fresh water.

 

[vyv_cox]

Engine warms up quicker, engine runs hotter and more efficiently, makes hotter fresh water.

When I had a Bukh DV20 there was no reason at all to suppose that it was not indirectly cooled. I suspect it actually warmed up more quickly than one with a heat exchanger as the volume of water is less. With the thermostat closed no water is flowing through the passages.

There may be a small efficiency reduction but this is hardly noticeable in a small auxiliary engine.

Domestic hot water was too hot for my hand within 15 minutes of engine running.

 

[Sailaway1949]

Welcome to the forum. I'm not familiar with a DV24, but have converted my own RM90 10hp single diesel.
It's simple enough, but involved quite a number of components, which might put some off.
My engine has an internal impeller, in much the same way as most other engines. This is still the case, but the input to the engine comes from the output of the heat exchanger, and then though the engine and out to the input of the heat exchanger. A simple closed loop cooling system of fresh water.
I didn't want to have a mechanical thermostat with seawater flowing through it, so made the system with 2 diaphragm electric pumps, which pump seawater through either the heat exchanger and the exhaust, or just the exhaust, depending on the engine temperature. Which pump is running is dependent on the engine temp, which by way of having a capillary thermostat (as a cooker does) to a relay, switches on the appropriate pump: if the engine needs cooling the seawater is pumped through the heat exchanger, so that once the engine temperature is at the correct 'coolness', the relay switches to the exhaust only pump. With this method the exhaust has a continuous flow of cooling water.
The pumps are manually 'activated' after the engine has started which avoids any issue of flooding the engine, should it have trouble firing up. From this same switch the alternator is also activated; it's a small engine and as such can have problems labouring when initially starting trying to charge the batteries. I've never had an issue with 'forgetting' to activate this switch, as it's part of the starting procedure as much as making sure the seacock is open.
It sounds far more complicated than it really is, and it works well with 'dozens' of hours on it during my curtailed summer of sailing, indeed I see no reason to alter it.
I made it like it is because the option of having a mechanically driven pump would've required a good deal of work adding frame and pulleys to another impeller pump.
Each diaphragm pump is about £20, and the capillary thermostat £15 or so, and readily available.
Redundancy is built in; if a pump goes down, then simply either adjust the thermostat or change to the 'other' pump. If both electric pumps break, then revert to the impeller by rearranging the 2 hoses. If the impeller were to fail, then one can use either of the electric items to cool the engine. All hoses are interchangable.
The engine system is unpressurised, and has a header tank from a Ford Fiesta, through which the thermostat is fitted to control the relays. The heat exchanger for mine is 22kW, and trouble free with standard fittings and widely available.
Nothing here is 'Yottie' stuff, out of preference.
Many might roll their eyes, but other reliable options aren't widely available, and won't cost under £100.
I do have an association with this type of 'machinery' so wasn't unduly threatened by the few relays and piping, which others might rightly prefer to avoid.

Thanks Jamie. I am at the design stage so any suggestions are most welcome.

 

[Sailaway1949]

Hi guys,
Many thanks for all your kind responses which I will take stock of. The general consensus seems to be why complicate things Good advice I think.

 

[vyv_cox]

Hi guys,
Many thanks for all your kind responses which I will take stock of. The general consensus seems to be why complicate things Good advice I think.

You may find this page of my website useful Calorifier installation

 

[Poignard]

Not for me to tell you what to do, but I can tell you that my BUKH DV10ME engine is 40 years old and I have owned it for 25 of those years, and I have never felt it would be better if it was FW cooled.

 

[jamie N]

With my own engine, when I bought the engine (as a non-runner), I removed the head and was 'surprised' by how completely congested the block was. There was the merest of channels from the seawater inlet through the block, and the head to the exhaust. It appeared to me that the flow would've looked OK, but basically the block was encased in crystallised salt. The block took a time to clean up with lots of water, a screwdriver and frequent soakings in a bucket. The thermostat was caked in salt and locked in a 1/2 open state. The channel through the head was directly past the area where the temperature sensor is, so my theory is that the engine had been running hot, with the cooling water making the temp. gauge appear quite normal. I've no idea how this affected the actual use of the engine, as I never saw it running, but have heard from people who had, that it'd always had 'issues'.
Because of those things, it was an easy decision to modify as in post #02, having a mind towards it being a bit of a project, and that I'd always be able to make it directly raw water cooled if 'my' way wasn't working, as Antartic Pilot moots in post#04.

 

[LittleSister]

Bukh documentation says indirect cooling is only warranted if the engine does more than 500 hours per annum. It doesn't state the logic behind that.

An indirect cooled engine thermostat will be set to run hotter (IIRC 70-95 degrees C as against 50-75 C for the directly cooled one). The directly cooled one can't be run as hot as the temperature will result in salts etc. precipitating out of the seawater. The engine runs more efficiently at the higher temp = lower fuel consumption, plus, of course, absence of fouling in the passageways needing occasional acidic flushing.

The Bukh conversion parts are horrifically expensive, especially the engine driven (freshwater) circulation pump (at least on the Bukh 36 I have - over £1,000!). I have, however, a Bukh DV 10hp on another boat that has been converted to indirect cooling by addition of two belt driven pumps, with the drive taken off a boss with two pulleys that fixes onto the flywheel (a standard Bukh part, I believe). The seawater pump replaces the one normally directly driven by the engine, and the freshwater pump is extra. Both are mounted in front of the engine on a rectangular horizontal frame made of angle iron bolted to all four engine mounts. The heat exchanger is a standard part from Bowman a heat exchanger manufacturer whose name escapes me just now (will update when it comes back to me). There is some minor modification to the arrangement of fittings on the thermostat housing, but other than that it is just connected by hoses.

Others have described using an electric pump to circulate the freshwater in converted Bukh DVs without problems, but I haven't found an 12v electric pump with the volume capacity to anything like match the Bukh direct drive mechanical freshwater circulation pump for my DV36 (135 litres/minute, compared to only 35-42 litres/min for the seawater pump!).

I would think the conversion using Bukh parts to make it the standard indirect cooled version of the engine would probably cost in the region of £2,000, while doing it like the Bukh DV10 conversion I described above might more like about £650, assuming you could make and fit the frame yourself.

I doubt it's worth it, but good luck if you go ahead, and let us know how you get on with it.

 

[penfold]

I suspect Bukh's argument is based mostly on the cost of conversion. Bowman is the most common heat exchanger make in the UK. A fresh water circulation pump could be made using a car water pump on a fairly simple backing plate at a fraction of the ridiculous sum Bukh want, but not many people have the skills or inclination to do so.

 

[LittleSister]

I suspect Bukh's argument is based mostly on the cost of conversion.

I think the Bukh advice is intended to inform choosing between the two different factory versions - indirect or direct - rather than conversion. (Though I think the DV models are now only sold as indirect because they are sold almost exclusively for lifeboats these days. They have many more modern models than the DVs, but none, I think, are small auxiliaries.) But my query was really about why a particular higher annual hours justifies the extra cost and complication of indirect cooling - the corrosion associated with direct cooling isn't, I would assume, hours related, and the reduction in fuel consumption would not, I suspect make that much difference unless hours much higher than 500 were run.

Bowman is the most common heat exchanger make in the UK.

Yes, thanks for the reminder, it's a Bowman heat exchanger on the DV10 I talked about above.

A fresh water circulation pump could be made using a car water pump on a fairly simple backing plate at a fraction of the ridiculous sum Bukh want, but not many people have the skills or inclination to do so.

I think the freshwater pump on my DV10 is from a Ford van (nearest model number I could find to the one on the pump was an old Transit). That is a belt driven pump, and I don't know whether vehicle cooling pumps these days are commonly belt driven.

The replacement seawater pump, also belt driven, is a standard marine one, Jabsco or Johnson, I can't remember which.

 

[Lifeboater]

I may be missing a trick, but why bother? Raw water cooling is much simpler, and on an engine like the Bukh, I don't see the advantage. All you're doing is adding complexity and additional points of failure for doubtful advantages. The engine may run slightly hotter, and it may last a little longer. I doubt the second - something else will limit the life of an engine like a Bukh long before internal corrosion kills it.

An awful lot of engine related posts on here are related to problems with heat exchangers, to the extent that I see them as a problem waiting to happen.

Very true, although you do need to be careful with a build up of white worm inside the engine if it's not run too often, and changing zinc anodes. The most reliable cooling system is the very simple keel cooling which requires an external plate or pipes if the hull is a plastic or wooden one. The cooling plate can be fitted inside a steel or alloy hull, and if you like pipes, inside the bilges is also possible. Keel cooled diesels need far less servicing, no water filter to clean, no heat exchanger to service every year, (Clean and new seals), only one belt and no sea water pump to fiddle with or leak.