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Bukh DV24 cooling system


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2 hours ago, Tony Brooks said:

 

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?

I changed to one with a rubber seal. I pressure tested the tank etc with air and a blank cap at home and it held pressure. The recovery worked well but every now and then would fail. I talked with someone specialising in old Rover cars which had a similar system and he said that the same happened with Rover cars.

since my engine had never overheated and doesn’t use water I decided if it ain’t broke don’t fix it. You were a big help at the time and we discussed flash boiling etc.

i must admit that I was worried that if the tank level  was low the system would “pick up air” but after your comment that coolant will always be pushed over if everything is flooded assures me. 
one other comment was that I discovered that the allowable pressure is around 1 bar but limited to around 3psi due to the rubber end caps. I had stubs welded to my expansion tank getting rid of the rubber end caps and increased the pressure of the cap. 
all my hoses are decent coolant hoses and the recovery pipe was an 8mm thick walled new diesel hose so there should be no problems there. 
 

 

 

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2 minutes ago, Peugeot 106 said:

I changed to one with a rubber seal. I pressure tested the tank etc with air and a blank cap at home and it held pressure. The recovery worked well but every now and then would fail. I talked with someone specialising in old Rover cars which had a similar system and he said that the same happened with Rover cars.

since my engine had never overheated and doesn’t use water I decided if it ain’t broke don’t fix it. You were a big help at the time and we discussed flash boiling etc.

i must admit that I was worried that if the tank level  was low the system would “pick up air” but after your comment that coolant will always be pushed over if everything is flooded assures me. 
one other comment was that I discovered that the allowable pressure is around 1 bar but limited to around 3psi due to the rubber end caps. I had stubs welded to my expansion tank getting rid of the rubber end caps and increased the pressure of the cap. 
all my hoses are decent coolant hoses and the recovery pipe was an 8mm thick walled new diesel hose so there should be no problems there. 
 

 

 

 

Thanks. As long as the extra rubber seal under the cap made a good seal, then I don't see how it could not suck the coolant back, but that does not mean that I don't believe you. As you mention rubber end caps I suspect this is one of the Polar/Bowman manifolds like those used on BMCs, so I would not be surprised if the end caps were not collapsing under the depression, rather than sucking coolant back.

 

For others reading this topic. We pressurise the cooling systems to prevent localised boiling on certain hotspots inside the cylinder head and this is most likely to occur at high seeds and loads, so the majority of canal boats probably do not need to be pressurised at all unless they make a habit of pushing tides or high current flows for long periods of time. Fitting a higher pressure cap should not do any harm as long as it does not blow a hose off or split a rubber end cap, but it is unlikely to do much good either.

 

I note that I have seen the odd commercial vehicle with a 21psi pressure cap. I think it is all to do with engine power, coolant, and cooling capacity.

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8 minutes ago, Tony Brooks said:

 

Thanks. As long as the extra rubber seal under the cap made a good seal, then I don't see how it could not suck the coolant back, but that does not mean that I don't believe you. As you mention rubber end caps I suspect this is one of the Polar/Bowman manifolds like those used on BMCs, so I would not be surprised if the end caps were not collapsing under the depression, rather than sucking coolant back.

 

For others reading this topic. We pressurise the cooling systems to prevent localised boiling on certain hotspots inside the cylinder head and this is most likely to occur at high seeds and loads, so the majority of canal boats probably do not need to be pressurised at all unless they make a habit of pushing tides or high current flows for long periods of time. Fitting a higher pressure cap should not do any harm as long as it does not blow a hose off or split a rubber end cap, but it is unlikely to do much good either.

 

I note that I have seen the odd commercial vehicle with a 21psi pressure cap. I think it is all to do with engine power, coolant, and cooling capacity.

I thought higher pressure raises the boiling temperature which is why they are fitted to most engines in most applications. I contacted the engine manufacturer and they said that the 15 psi cap should be fitted. But then I do run at max from time to time eg Ribble Link. Trent, Severn, Thames etc

 

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Hi JR,

 

That's great - I guess if you worked there until 1979 there's half a chance you might have worked on my boat, if my boat is early 1980! I know my boat started out as a 30-footer but at some point was extended to 40 foot.

 

Yes Bukhs do seem to go on forever, I'm almost certain my previous engine (which was a DV10) was the one installed when the boat was first built. If so, that would have been 40 years service, even with a couple of previous owners to whom I think routine maintenance was a mystery. And even when it died altogether that was human error (flywheel bolts not torqued properly) rather than a genuine breakdown.

 

The downside is that (as I'm sure you well know), Bukh parts are eye-wateringly expensive! Replacement water pump on my DV24 was upwards of £600. Ouch.

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12 minutes ago, Peugeot 106 said:

I thought higher pressure raises the boiling temperature which is why they are fitted to most engines in most applications. I contacted the engine manufacturer and they said that the 15 psi cap should be fitted. But then I do run at max from time to time eg Ribble Link. Trent, Severn, Thames etc

 

 

It does, but the design of the cooling system should ensure that it can dump enough heat so it never boils. If this is not the case you would not have the engine temperature stabilising at around 80C to 90C, it would just keep rising until the engine boiled at the higher temperature, this can be most readily seen on canal boats with undersized skin tanks. At certain points inside the cylinder head water jacket like at the exhaust valve seats and around the injector nozzle hole, at high speeds and powers the heat passing through those hotspots is too much for the coolant to carry it away so left to itself steam bubbles would form on those areas. This has three effects, the steam pushes water away so it comes out of the cooling system, scale can form on the hotspots making them less able to transfer heat into the coolant, and from that you can get physical damage like cracks caused by the overheating of those local areas. As this tends to be fairly transitory, the system is pressurised to prevent that localised boiling.

 

Raising the pressure should not increase the running temperature, although with a marginal skin tank size it could make the difference between overheating and boiling or not, because the heat transfer through the skin tank wall is dependant upon the relative temperatures of the coolant and canal water.  So allowing the engine to run hotter before it boils allows a greater heat transfer out of the coolant.  However, if you allow it to run too hot it is likely to damage the thermostat, so it opens at a higher temperature than it should.

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My power is 18 bhp skin tank slightly small at 4ft2 (should be 18/4=4.5ft2). Also no baffles and slightly over thick 1.5inches.

 

Also had too much blacking on outside of tank. By putting thinner blacking over tank and higher pressure cap on expansion tank I have solved any potential overheating issues.

 

ideally I would have a thinner, slightly bigger tank with baffles but I have done a fair

bit of full power running over longish periods without any overheating so all is well. The slightly over thick tank which means that there is more coolant than is necessary explains why the expansion tank seems slightly small but works well

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