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Calorifiers and hot water


Guest plesbit

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As full members will likely know we recently picked up our new (to us) boat. However we appear to have come across a problem I simply had not anticipated - no hot water, plenty of warm but nothing hot.

The problem basically is that the engine, which is a relatively powerful seagoing jobby (Volvo AD41P) doesn't really get warm at river speeds, I don't think the engine exceeded 45C and that was doing 6mph. Obviously if the engine doesn't get above 45C then the water temperature will be even less. And this is mid summer - I doubt it will even get on the scale in the winter.

When fully warmed up the engine should run at around 80C which would be just fine - but clearly at river speeds she doesn't even know she's got out of bed. So at the moment it would not be possible to have showers on board.

Now this cannot be a one off issue - we're only 200hp so there are far more powerful engines running around the broads at 6mph and less. I'm sure people on some of those big Brooms are not doing without showers so there must be a solution. Any ideas?

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Simon,

Can an immersion be fitted to your calorifier? I have a 1.5Kw immersion fitted in my calorifier and a 1.8Kw invertor. Whilst the engine is running the invertor is not really draining the batteries and this can be used to power the immersion. In my case I use it to get hot water quickly if only cruising a very short distance. It is also useful in the Winter, because the calorifier means it takes even longer for the engine to reach the normal running temperature, which is already delayed by the colder river water.

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You could restrict the raw water flow until she reaches temperature, the same effect as the old radiator blinds on cars & trucks. Hot water is the least of your worry if the engine is running at below operating temperature as the condensates will never get the chance to boil off. Actually even at river loads she should reach temperature in about 45 mins or so anyway but if you fancy short trips to your favourite evening spot why not consider a little “kicker†on a bracket to get you over there, it will save wear on the main engine.

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Is the engine thermostat working properly Simon? I would have thought that even at tick-over an engine should reach normal operating temperature, as the the thermostat should close down most of the coolant flow until that point in reached?

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Another thought occurs Simon, we have already discussed winter projects one of which is replacement heating. Perhaps you might consider one of the Webo or Ebo wet systems, that will heat the water and provide general warm air heating through a matrix. You could even warm up the engine before starting it if you wished.

It is something I have been meaning to do myself for some time and will almost certainly fit it to our next boat.

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There is an immersion in the tank but it is set to run off shorepower only and there is no inverter.

Thermostats. Well I did wonder about this. On a car I assume the thermostat starts off closed so that water only circulates around the engine as it warms up and then once it reaches temperature it opens to allow water to flow to the radiator to be cooled, returning the cooler water back into the system and thereby regulating the engine temperature. Obviously marine engines have a heat exchanger instead of a radiator and use raw water instead of airflow to take away the heat from the sealed system. Up to that point I think I understand it. But the calorifier changes the rules since it acts much like a second heat exchanger.

{Deleted the rest because of what I have since found out}

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Okay, had a quick look through a KAD42 cooling system manual. Judging by the text below, the system does indeed act in much the same way as a car - as you would expect. However the manual makes no mention of a calorifier and deals strictly with the engine. From memory the out and return pipes for the calorifier come off the heat exchanger tank, at least they did on Silver Dream, so in order words if the thermostats are functioning correctly then water should not be getting circulated to the heat exchanger OR the calorifier until the closed cooling circuit is warm enough to open the thermostats. So either they are opening too soon or not closing at all otherwise we should not have had any hot water whatsoever. At least that is my understanding.

From the manual:

The engines are liquid cooled and equipped with a closed cooling system. The system is divided into two circuits. Coolant is pumped around the inner circuit (the freshwater system) by a centrifugal type coolant pump. The coolant pump is driven from the crankshaft using a drive belt. The coolant is pumped from the coolant pump out to a distribution channel in the cylinder block and is pumped around the cylinder liners and onward through the cylinder block.

From the cylinder head the coolant passes out through the exhaust pipe, passes the turbocharger turbine housing and then returns to the thermostat housing where two thermostats regulate the engine coolant temperature. As long as the coolant is cold the thermostats shuts off the flow to the heat exchanger. The coolant travels through a by-pass line under the thermostats directly back to the intake side of the pump.

When engine coolant temperature has risen to a certain temperature the thermostats open and allow coolant through to the heat exchanger, at the same time the by-pass line is closed. In the heat exchanger heat from the coolant is transferred to the seawater before the coolant is returned to the coolant pump.

Large amounts of heat are also dissipated by lubricating oil which transfers the heat to the seawater system via the oil cooler.

The lubricating oil is also used to draw heat off the pistons in the engine see Workshop manual “Group 22 Lubricating systemâ€

The cooling system can operate with a certain amount of overpressure. The risk of overheating is decreased therefore if temperatures become high. If pressure is higher than usual, a pressure valve in the filler cap opens. Through flow in the seawater system is provided by an impeller pump directly driven by the injection pump shaft. The seawater passes through the engine charge air cooler (CAC), oil cooler, heat exchanger, exhaust smoke and in TAMD-, KAMD engines through the reverse gear oil cooler.

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I know all boat setups differ greatly, but here is what I have observed on mine which may give you some clues. From cold the engine temperature seems to climb fairly quickly to 60 degrees, where it then stays for some 30 mins before then climbing to its normal operating temperature of 80 degrees. From this I have deduced that the calorifier is the other side of the thermostat, which opens at 60 degrees, hence the stall in climb of temperature as the calorifier then keeps the closed water cool until it also reaches 60 degrees. This is further backed up by the fact that if I use the immersion on shorepower to heat the water in the calorifier, then start the engine, the temperature climbs fairy linearly to 80 degrees without stopping at 60 degrees for 30mins.

Can you tell whether the pickup to the calorifier is before or after the thermostat? Can it be moved to after the thermostat fairly easily, to facilitate the engine warming to normal temp quicker before attempting to heat the calorifier? Firstly I would check that the thermostat is not stuck open. If the system is like mine above then it would be trying to heat the closed and calorifier water from cold with the thermostat stuck open, and on mine when the thermostat opens the temp sticks at 60 degrees for a fair while, if it was stuck open, then I could see it being a very slow warm up from cold.

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The major problem (if it can be called a problem) with higher performance marine engines cooling systems is that they have over capacity to allow for furring up of the exchanger stack, minor blockages in closed and raw water systems etc. Our D4 225 always comes up to 85c on the rivers but it does take four times longer than if given a little work to do. Never underestimate the massive cast iron bulk of even modern marine diesels, that takes a bit of heating up (and cooling down) It may be that your thermostat is opening too early and that is worth confirming / discounting. If all else is working as it should I would certainly have a look at restricting the raw water flow on a controllable basis.

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Keith’s observations are correct and standard for all properly fitted calorifiers, the KAD42 has a specific blanked take off and return after the thermostat. It is difficult if not impossible to compare the behaviour of a small riverboat motor with one of a higher horsepower as if operated at designed load they will both reach temperature in a similar time, the issue here is how to reach temperature more quickly when the unit is not producing much waste heat because it is doing bugger all work. The only way to do that folks is to restrict the cooling somehow, physics unassailable physics.

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Any comments on my observation David? Basically if I read correctly heat exchanger is not even used unless the thermostats are opened, otherwise the coolant is simply returned to the system via a bypass. This is backed up by Keith's description above. Since our temperature gauge indicated a coolant temperature of about 45C then the thermostats should not have opened, ergo no flow to heat exchanger, ergo no flow to calorifier, ergo no water heating of any kind. We had warm water so there was definitely a heating effect in the calorifier.

So from that my guess would be that either the thermostats are at fault (opening too early or not actually closing properly when the engine is cold) or the calorifier installation is not as it should be and water is circulating to it the whole time - which would inevitably retard the rate it which the engine temperature rises. So, firstly I need to check the take off and return for the calorifier to see where the water is sourced and returned and, if correct, I need to remove and test the two thermostats. Yes?

I have further observations but I'll save them until I get a nod or shake on the above.

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Your observations are in the main correct Simon, a road vehicle and marine closed cooling system are actually identical in function, the only difference is that the car heat exchanger (commonly called a radiator) uses air and the marine heat exchanger uses water to remove excess heat from the oil and engine coolant, the car also has a bit of airflow around the engine when in motion. In both there will always be a little flow through the exchanger even with the thermostats in the closed condition via the bypass, a safety feature guarding against thermostat failure or blockage. Also there will always be permanent cooling via the oil cooler which is quite large and water is much better at conducting heat away than air. In truth I doubt that there is anything actually wrong with your setup, just that it is not working to it’s design specs.

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In truth I doubt that there is anything actually wrong with your setup, just that it is not working to it’s design specs.

Hmm, meaning what? That there is a problem or that the engine simply is not generating enough heat to warm up properly because it is not being made to do any work?

The oil cooler, which appears to be cooled entirely by raw water, was something I was going to ask about as it implies that even without the heat exchanger on the sealed system there is still a significant cooling effect in place from the moment the engine starts turning. My fear is that the problem will get even worse as the weather and water temperatures cool in the Autumn / Winter.

Kingfisher is slightly more powerful, yet she heated up to 85C, even on the rivers just taking longer to get there. I could go all day and I don't think Grenick will ever get up to temperature - indeed we punched the tide out to Surlingham Ferry which got the engine temperature to about 45C and then we got a push on the return leg. The lower revs on the return leg actually caused the engine to cool to just over 40C so, on that basis, I cannot see that a longer trip would have made much difference.

How would you restrict the flow of raw water?

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Hmm, meaning what? That there is a problem or that the engine simply is not generating enough heat to warm up properly because it is not being made to do any work? ?

In a word, yes

How would you restrict the flow of raw water
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Okay, your engineering knowledge is largely unparalleled in these forums (and others) so I'll take that seriously but, for the sake of argument, there is one minor kink in that theory which does not seem to be adequately explained. And that's this; the AD41 is arguably the most successful engine Volvo ever produced. They are everywhere - and the KAD42 is essentially the same engine with the addition of a supercharger - then there's the KAMD and TAMD42's as well. There must be hundreds and hundreds of these engines trundling around the Broads, many of them in pairs. If this is an inherent issue then a heck of a lot of people must be affected by it and by extension anyone with similar (or larger) engines from other makers. Do none of these people ever shower? So why did you not see the same issue with Kingfisher?

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I'm not sure it would on a boat David. The Calorifier is heated more on a water bypass type affair, so the engine/heatexchanger setup is more than capable of keeping the engine at normal operating temp' , as can be shown by simply doing away with the Calorifier and blanking feed/return off.

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Thermostats is exactly where I intend to start. But I am still waiting for someone to explain why everyone else with a large engine is not experiencing exactly the same thing but no-one seems keen to have a go.

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It doesn't matter what size of engine it is, the fact that it's coolant will not circulate until the coolant temp reaches thermostat opening temp means it must be stuck open in my mind. The whole point of a thermostat in an engine is to achieve a normal operating temp' cheers

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I see your point Rod, but what will happen is that as some of the cold water that has been sat in the Calorifiers pipework enters the engine block, it does indeed lower the coolant temp, thus closing the thermostat again until the 80 C is re achieved again then re opens. This Ballet will go on until the water in the Calorifier has reached a similar temp to that of the coolants designed running temp. Usually 30 mins or so... cheersbar

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I feel a bit daft posting this with all you technical experts around :oops: but on our landlubin broadland boat :lol: we have a Thetford duel fuel waterheating system which heats the water brilliantly using either bottled gas or 240v at the flick of a switch. Whould one of these systems solve your problem Simon? the entire unit including insulated tank fits under one bench seat and holds enough hot water for us both to shower before needing about 10 mins to recharge up to holding near boiling hot water again, suppiled via domestic type taps.

Julz :wave

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Yes Rod, Simon's water is only reaching luke warm at best, which to me points to the engines thermostat being stuck wide open and thus not allowing the 80c to be achieved before opening and moving the coolant on to warm the next lot up! cheers

Other theories are available though! :lol:

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