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Raising engine coolant tank


Strettonman

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I plan to fit a calorifier in the engine bay but I’ve just seen something saying the calorifier coil needs to be below the engine coolant tank. I have a cruiser back with a 1.5 BMC diesel with a metal water reservoir across the top of the engine about 20cm below the deck. The side platform I want to put the calorifier on means it is touch and go whether the coil will be below the engine water height. 

Firstly, is it right that the coil needs to be lower then the engine water height ? I presume air will always find the highest point so would end up in the coil and water would come out of the engine coolant filler cap when you open it. 

Secondly, can you buy/fit a tank on top of the existing one or fit a different tank to lift the level up the near deck height. 

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Our calorifier sits on the swim next to the engine, which has a header tank on the engine. Difference in height can only be an inch or two and it works

 

I guess the advice is to do with bleeding air out of the calorifier coil

 

Richard

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1 minute ago, Strettonman said:

Richard. Is the header tank  a couple of inches above the top edge of the calorifier or the highest coil inlet for the coolant ?

 

The top of the header tank is a few inches above the top of the calorifier

I can't tell you exactly how much as the engine is out of the boat and spread through two different workshops, so I can't measure it at the moment

 

Richard

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12 hours ago, RLWP said:

Our calorifier sits on the swim next to the engine, which has a header tank on the engine. Difference in height can only be an inch or two and it works

 

I guess the advice is to do with bleeding air out of the calorifier coil

 

Richard

 

Yes, our last shareboat had a horizontal calorifier under a semi-trad stern deck and it was a bu**er to bleed. Had to resort to using a mains pressure hose to flush the air bubbles out once. 

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If you have a BMC engine that only has the "header tank" on the engine itself, I reckon it is always a useful improvement to add an additional one at a higher level.

 

Even without considerations about adding and bleeding calorifier coils, it avoids the old chestnut of having to run with the engine based "header tank" only (say) half full, to avoid coolant being ejected as things heat up.

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16 minutes ago, alan_fincher said:

If you have a BMC engine that only has the "header tank" on the engine itself, I reckon it is always a useful improvement to add an additional one at a higher level.

 

Even without considerations about adding and bleeding calorifier coils, it avoids the old chestnut of having to run with the engine based "header tank" only (say) half full, to avoid coolant being ejected as things heat up.

I can't see the advantage, Alan. The header tank on the engine (usually a 'Bowman' heat exchanger with no tubestack) is several times bigger than most header tanks. Ours doesn't throw out coolant using the simple test of 'stick your finger in the tank, if it is wet it's OK'. That's a long way past half full

 

Richard

 

What size header tank have you got on Sickle?

Edited by RLWP
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45 minutes ago, Mike Jordan said:

If you are feeding the calorifier coil from the original heater feed pipe and returning the flow to the bottom hose, I would expect the engine water pump to push any air out of the coil without problem.

Providing the flow goes to the bottom connection of the coil so that the air is pushed up to the top.

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Had this discussion here before. But I will say it all again, but please no argument, I am a professional.

Briefly if its a pumped circulation and not gravity, yes it should. Putting the hot water into the coolest area of the cylinder improves the heat transfer rate and its easier to vent air upwards rather than try to push it downwards.

The reverse is true on gravity systems but then you would have a vent to a tank off the top connection to get the air out. Can't do that here as the system has to be pressurised to the engine pressure.

40 years as a technical heating engineer says so. 

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1 minute ago, Boater Sam said:

Had this discussion here before. But I will say it all again, but please no argument, I am a professional.

Briefly if its a pumped circulation and not gravity, yes it should. Putting the hot water into the coolest area of the cylinder improves the heat transfer rate and its easier to vent air upwards rather than try to push it downwards.

The reverse is true on gravity systems but then you would have a vent to a tank off the top connection to get the air out. Can't do that here as the system has to be pressurised to the engine pressure.

40 years as a technical heating engineer says so. 

So would you advocate doing that with the skin tank as well?

 

Same arguements could be applied, surely?

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I'm not in the mood to argue but if you stop being difficult and think for a moment you will realise that the situation with a skin tank is different.

 

The tank is below the engine level, not above so it will always fill with water totally when bled of air. The direction of flow in a skin tank on the swim is not at all critical provided it can be bled of air. 

The easiest way to vent the top of the tank to remove the majority of the air is into the engine to vent out of the "radiator" cap. So the top of the tank connects to the top of the engine. 

Water "pumps" on engines are not positive displacement ( except piston pumps on antique engines) but rather circulators like a central heating pump. Providing there is no air, it will circulate water, just as central heating pumps do, in either direction.

In fact there are many boats with base plate tanks with effectively no top or bottom flow connections.

Edited by Boater Sam
Grammatical correction
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10 hours ago, Mike Jordan said:

The flow of water in a skin tank is critical! If you put the hot in at the bottom it will immediately rise to the top and be returned to the engine with little cooling on the way.

Absolute rubbish, sorry.  Ever heard of baffles? moving water mixes? stir a cup.

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19 hours ago, Boater Sam said:

Had this discussion here before. But I will say it all again, but please no argument, I am a professional.

Briefly if its a pumped circulation and not gravity, yes it should. Putting the hot water into the coolest area of the cylinder improves the heat transfer rate and its easier to vent air upwards rather than try to push it downwards.

The reverse is true on gravity systems but then you would have a vent to a tank off the top connection to get the air out. Can't do that here as the system has to be pressurised to the engine pressure.

40 years as a technical heating engineer says so. 

Connecting the outlet from the engine to the top of the calorifier coil will result in useable hot water being available sooner, both because it's the top of the tank being heated, and greater heat transfer from coil to tank, due to counter flow.

 

However, the advantages of doing it the other way round are ease of bleeding (self bleeding in many cases) and elimination of the possibility of the calorifier cooling by heating the engine by convection when the engine is cold.

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Hot water rises and ciold water falls.  Like vehicles. Heated water from top of engine to topmost connction on radiator. Return, bottom of radiator to lower connection on engine. Old cars like Ford E93A ect thermo syphoned beautifully. 152 years motor and marine mechanic so don't dare argue with me I'm not in the mood.  :angry2:

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2 minutes ago, bizzard said:

Hot water rises and ciold water falls.  Like vehicles. Heated water from top of engine to topmost connction on radiator. Return, bottom of radiator to lower connection on engine. Old cars like Ford E93A ect thermo syphoned beautifully. 152 years motor and marine mechanic so don't dare argue with me I'm not in the mood.  :angry2:

Oh yeah? Well - my dad is bigger than yours

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44 minutes ago, bizzard said:

Hot water rises and ciold water falls.  Like vehicles. Heated water from top of engine to topmost connction on radiator. Return, bottom of radiator to lower connection on engine. Old cars like Ford E93A ect thermo syphoned beautifully. 152 years motor and marine mechanic so don't dare argue with me I'm not in the mood.  :angry2:

Perhaps 152 years is either too long or not quite enough. Never too old to learn but you can't teach old dogs new tricks.

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