Bukh DV36 life

[robertager1962]

I have a DV36 and just a couple of points that some of the contributors may have slightly muddled (unless they have different configurations to mine) . The fresh water cooled DV36 does not have engine anodes, just an anode in the heat exchanger. Also the electric circulating pump for the water is on the port side of the engine at the front (flywheel end).
They are a low revving engine with a very high torque and provided they are maintained, should last well over 4,000 hours.
A mod that I have added to mine is a freshwater flush which flushes the raw water side with fresh water water when I leave the boat for periods of a few weeks or more. This has definitely helped with corrosion in the exhaust elbow and wastage on the anode in the heat exchanger. It is also a good way to get antifreeze into the raw side of the system.

 

[robertager1962]

I've a 1979 Bukh DV36, direct seawater cooled, with 2,000 odd recorded hours on it. Starts and runs very well (though I did have an injector pump seal failure recently). I would not be put off by one with 4,000 hours, though I would want to see it start and run, and ideally have an engineer check it over.

I have not heard of the water pump having the same problem as the DV10 & 20 series (i.e. if the pump seals fail without early leaking being spotted coming from the weep holes, water gets into the engine), but that does remind me to check the potential for that. (The DV36/48 is a significantly different layout, later design, engine to the DV10/20, though they do share some parts.)

The seawater pump is on the starboard side near the rear of the engine, facing forward, somewhat hidden under the exhaust manifold, and driven by the camshaft etc. gears on the back of the engine. The Bukh freshwater circulation pump (if fitted) is to the rear of that.

The anode is on the starboard hand side of the engine, half-way up, about 1/3 of the way back from the flywheel. There is a big nut in that location (22mm?) which unscrews. The anode, which IIRC is the same as that for the DV10/20 series, screws into the other face of it. Unlike a previous poster, I would be unconcerned by finding a wasted anode That's what they do. Just replace it. There was a discussion on here about Bukh anodes a while ago, and one poster says he's never replaced his, and it has been fine for 30 years.

I'd be interested to know the make/model of the electric circulation pump on your engine when you get to see it. I toy with the idea of converting to indirect cooling, but the cost of the Bukh gear driven circulation pump is unpalatable, and I haven't seen an electric pump with the same capacity.

My electric circulation pump is a Johnson Pump Model CM30P7-1. It works well but you just need to bear in mind that it is a fixed speed pump so if you gun your engine it won't speed up with the engine revs so I don't. The pumps are beautfully engineered. I keep a spare but haven't needed it in 3 years of boat ownership and a Biscay crossing (mostly motoring)

 

[LittleSister]

My electric circulation pump is a Johnson Pump Model CM30P7-1. It works well but you just need to bear in mind that it is a fixed speed pump so if you gun your engine it won't speed up with the engine revs so I don't.

Thanks for that. Most helpful.

Do I take it, then, that the pump can't cope with the engine at full power (i.e. the engine overheats if you do that)?

 

[robertager1962]

Thanks for that. Most helpful.

Do I take it, then, that the pump can't cope with the engine at full power (i.e. the engine overheats if you do that)?

Hi I haven't really pushed it that far to actually let it overheat. We have a massive 2 bladed prop on our Southerly 105 and if I go more than about 1700 rpm the prop starts to cavitate. I have pushed it hard for a bit and the temperature has gone slightly above the mid way but not too much. I did have a Stainless steel muffler that always kept the temperature below normal but this started to leak and I changed it for a vetus plastic one. Although it is recommended for 36hp engines I have my doubts as the temperature is now just above normal but never really varies. I was slightly concerned when we first set out from England but we have done all the Brittany coast, Biscay and North coast of Spain and it has never been any problem (touch wood). My main thing has been to flush my engines with fresh water when it is left. In previous boat (a Centaur) I had an ancient Volvo MD2B which I nursed along and it was a treasure. I started doing this using a 5 gallon jerry can that I used to fill up with tap water. This appeared to be successful so when I bought my Southerly I added a 1 gallon water tank which is fed from my pressurised fresh water system. Basically I shut of my sea water intake and fill the 1 gallon tank, start the engine and then open the valve to my fresh water supply. After about 2 minutes the engine overtakes the supply from my tank (it is translucent and I shine a torch through it to check the water level.) I think that to retro fit your engine with a fresh water system may be prohibitively expensive as the heat exchangers are very pricey (I have a Martec) but it may be worth looking at a fresh water flush. My bits to fit this cost me about £50.00. If you are interested I can send you a picture of the installation.

 

[LittleSister]

I wouldn't want to be restricted to1,700 rpm, even though my engine is oversized for my boat (the standard is 20hp). I wonder whether it's practicable to have two electric pumps in parallel, with one continuous, and the other just cutting in at higher temperatures or revs. I've now found a circulation pump with a significantly higher capacity (SPX Johnson CM90 BL), but it draws about 9A.

I ponder about changing to freshwater cooling, but probably won't ever get round to it. It's lasted OK 40 years, and Bukh advise it only for engines doing over 500 hours per annum.

It would be incredibly expensive to do it using new Bukh parts, but I've had another boat that had a DV10 converted by addition of a belt driven circulation pump, and a Bowman heat exchanger/header tank (the latter about £300 or so).

According to the current Bukh DV36 manual the capacity of the standard (gear driven) pumps at 3,600 rpm is -
Direct cooling
Seawater pump: 24 - 30 litres/min
Indirect Cooling
Seawater pump: 36 - 42 litres/min (same pump as direct cooled version, but different cam)
Freshwater pump: 135 litres/min.
I've no idea why, or whether, the freshwater pump needs such a big capacity. Maybe it's just so there's sufficient flow when it's turning at a fraction of maximum revs.

Thanks again for the info.

 

[robertager1962]

I wouldn't want to be restricted to1,700 rpm, even though my engine is oversized for my boat (the standard is 20hp). I wonder whether it's practicable to have two electric pumps in parallel, with one continuous, and the other just cutting in at higher temperatures or revs. I've now found a circulation pump with a significantly higher capacity (SPX Johnson CM90 BL), but it draws about 9A.

I ponder about changing to freshwater cooling, but probably won't ever get round to it. It's lasted OK 40 years, and Bukh advise it only for engines doing over 500 hours per annum.

It would be incredibly expensive to do it using new Bukh parts, but I've had another boat that had a DV10 converted by addition of a belt driven circulation pump, and a Bowman heat exchanger/header tank (the latter about £300 or so).

According to the current Bukh DV36 manual the capacity of the standard (gear driven) pumps at 3,600 rpm is -
Direct cooling
Seawater pump: 24 - 30 litres/min
Indirect Cooling
Seawater pump: 36 - 42 litres/min (same pump as direct cooled version, but different cam)
Freshwater pump: 135 litres/min.
I've no idea why, or whether, the freshwater pump needs such a big capacity. Maybe it's just so there's sufficient flow when it's turning at a fraction of maximum revs.

Thanks again for the info.

I think the main issue with the electric water pump is that it is not speed regulated so needs to pump more water to be capable of cooling at maximum revs.
2000 rpm for me is hull speed so not much point trying to push it any faster really. I fitted an hour meter and over the past few years I have worked it out to 1.5 litre per hour, not bad for a 36hp engine.
Got a leaking water seal in the raw water pump at the moment so just waiting for spares from UK. Bukh dealer in Southampton told me they were shut for a minimum of 6 weeks. Thank heavens for ASAP supplies!
Take care

 

[LittleSister]

Thank heavens for ASAP supplies!

T. Norris seem to keep a good range of Bukh spares (and can get the rest). I've had good service from them.

 

[Fr J Hackett]

I bought a boat with a Yanmar 30 GM with an electric pumped fresh water cooling system. It would overheat if the engine was run for a few hours at 2800 RPM + the previous owner had a jury rigged system to convert to direct cooling. I put up with it for 6 months before I bought the Yanmar belt driven system. A year later the rear crankshaft oil seal failed, I remain convinced that the continual overheating caused that problem. I would be very wary of it.

 

[jtwebb]

My original question has turned up a very good and interesting set of comments. I really need to find a way of looking at the LM32 which triggered this off. I am left with much good information.

 

[jtwebb]

. The system works with an electric pump to circulate the fresh water.


Novel, I'd definitely have a spare pump aboard!

I have the boat now. The previous owner was sufficiently cynical to have a spare pump already there! Also enough bits to rebuild the Brunton prop if that gave trouble.