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Expansion Tank for BMC Engine


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Hi folks , dont know if this will help but go on kinver boat services web sit and you can view ther expansion tanks ,they look cool but are not cheap (£150.00) but they have blow off valve ,glass level gauge ,pressure tasted and you state the feed size pipe

 

See Ya

Leechy

I think I'd try David's suggestion with a washing-up liquid bottle, baked bean tin & length of plastic hose first !

 

Might represent a considerable saving over this more sophisticated option :wacko:

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I think I'd try David's suggestion with a washing-up liquid bottle, baked bean tin & length of plastic hose first !

 

Might represent a considerable saving over this more sophisticated option :wacko:

 

I actually used a Tesco's 500ml liquid hand soap bottle with the plunger mechanism removed. They are much stronger than washing up liquid bottles - anyway most of them are not round these days so they won't fit inside a baked bean can.

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  • 11 years later...
7 hours ago, Neil Smith said:

Read the above suggestions.

Neil

I think Graham is possibly looking for a header (expansion) tank rather than an overflow tank, Calcutt sell one for about £20 plus postage, the alternative is a car breakers yard.

http://calcuttboatsshop.com/epages/c3a6cb0f-3e0f-4132-9636-974f7502e04d.sf/en_GB/?ObjectID=57009&ViewAction=FacetedSearchProducts&SearchString=header+tank&FacetValue_CategoryID=1643370See:-

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On ‎25‎/‎02‎/‎2006 at 00:17, David Schweizer said:

 

1. Fit a new pressure cap, I find that it needs to be replaced about every couple of years. It should be a 4lb short reach one. Halfords don't seem to stock them any more, but you shold be able to get one from any decent Motor factor (I have the QH part number somewhere if you need it)

 

2. Connect a length of plastic tubing from the header tank overflow into a non pressurized overflow tank, making sure the pipe reaches the bottom of the overflow tank. Most of the overflow water will be sucked back overnight, and as already suggested any surplus can be poured back in when the engine is cold in the morning. (my overflow tank comprises a redundant liquid soap bottle held in a baked bean can bolted to the side of the engine box)

 

 

 

 

How does the overflow drain back to the engine? Any overflow will during operation will occur by excess pressure lifting the cap. Once the pressure is relieved the cap will close off sealing any return. If you have a bowman heat exchanger, then the engine coolant should be minimal, being cooled by the secondary water from your skin tanks. The skin tank water would have been circulated by a Jabsco pump or similar. Unfortunately many were 'modified' by people who should know better, and the Jabsco pump was taken out with the skin tank piping adapted to circulate skin tank water round the engine. The new volume is too much for the Bowman to cater for expansion, and if only the normal BMC water pump was retained there was a real chance of it being unable to cope with the extra resistance of the circuit leading to overheating. The only CB marine conversions I have seen incorporate a Jabsco pump adapted to the BMC water pump drive. If you go the way an additional expansion vessel to cater for expansion, then you need to adapt your original cap to permanently open with a pressure cap on the new bottle. If you incorporate an open expansion vessel, then as long as there is sufficient height to maintain a 4lb static head, then that could also work.

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32 minutes ago, Ex Brummie said:

How does the overflow drain back to the engine? Any overflow will during operation will occur by excess pressure lifting the cap. Once the pressure is relieved the cap will close off sealing any return. If you have a bowman heat exchanger, then the engine coolant should be minimal, being cooled by the secondary water from your skin tanks. The skin tank water would have been circulated by a Jabsco pump or similar. Unfortunately many were 'modified' by people who should know better, and the Jabsco pump was taken out with the skin tank piping adapted to circulate skin tank water round the engine. The new volume is too much for the Bowman to cater for expansion, and if only the normal BMC water pump was retained there was a real chance of it being unable to cope with the extra resistance of the circuit leading to overheating. The only CB marine conversions I have seen incorporate a Jabsco pump adapted to the BMC water pump drive. If you go the way an additional expansion vessel to cater for expansion, then you need to adapt your original cap to permanently open with a pressure cap on the new bottle. If you incorporate an open expansion vessel, then as long as there is sufficient height to maintain a 4lb static head, then that could also work.

Well there is quite a lot there!!  The BMC 1.5 in my boat used the standard engine pump to circulate the water through the skin tank, with no overheating problems. Furthermore the same pump also pumped the coolant round the central heating system, when the appropriate stops valves were opened. Whether Balliol Fowden, who designed the system "should have known better" is therfore a matter of conjecture, but I suspect he knew exactly what he was doing as the system worked well.

The heating system had an expansion tank at the far end, and any water which was released through the 4lb psi pressure cap into the tank was sucked back when the system cooled down. much of the water released through the 7lb psi pressure cap on the Bowman was not sucked back, but could be returned to the heat exchanger in the morning as part of the preparation checks before starting the engine.

As for water not retu

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4 hours ago, Ex Brummie said:

How does the overflow drain back to the engine? Any overflow will during operation will occur by excess pressure lifting the cap. Once the pressure is relieved the cap will close off sealing any return. If you have a bowman heat exchanger, then the engine coolant should be minimal, being cooled by the secondary water from your skin tanks. The skin tank water would have been circulated by a Jabsco pump or similar. Unfortunately many were 'modified' by people who should know better, and the Jabsco pump was taken out with the skin tank piping adapted to circulate skin tank water round the engine. The new volume is too much for the Bowman to cater for expansion, and if only the normal BMC water pump was retained there was a real chance of it being unable to cope with the extra resistance of the circuit leading to overheating. The only CB marine conversions I have seen incorporate a Jabsco pump adapted to the BMC water pump drive. If you go the way an additional expansion vessel to cater for expansion, then you need to adapt your original cap to permanently open with a pressure cap on the new bottle. If you incorporate an open expansion vessel, then as long as there is sufficient height to maintain a 4lb static head, then that could also work.

 

If you examine a standard pressure cap, you will find that the brass bit in the centre of the cap will open to allow air or coolant to return to the heat exchanger when the external pressure is greater than the internal pressure. However, I have never got an overflow bottle system to work without using a pressure cap which has a rubber seal to the top of the hole it sits in. Otherwise, coolant goes out into the bottle OK, but when the system cools, air comes in under the top of the cap. I agree it's simpler to replace the pressure cap with a flat one with a seal on it, and pressurise the expansion bottle!

Our old shared boat, Copperkins, ended up with a pressurised expansion tank and an overflow bottle. That worked, as the pressure cap made a good seal on the plastic neck f the expansion tank.

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Many old B,M.C. cars had an expansion tank. I have used the rather nice brass expansion tan off an MGB in several boats,which works well and polishes up .The Bowman heat exchanger can be filled to the top and 1" of water in the expansion tank.As has been said,coolant will return to the Bowman via the little bleed in the Bowman cap,if the coolant expands to overflow it. I have added an expansion tank to my present Isuzu indirect system to prevent slight leakage of coolant to the bilge. The problem with not filling the heat exchanger to the top is that some of the tubes are not covered. This allows the engine to run hotter when running hard.

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20 hours ago, Iain_S said:

 

If you examine a standard pressure cap, you will find that the brass bit in the centre of the cap will open to allow air or coolant to return to the heat exchanger when the external pressure is greater than the internal pressure. However, I have never got an overflow bottle system to work without using a pressure cap which has a rubber seal to the top of the hole it sits in. Otherwise, coolant goes out into the bottle OK, but when the system cools, air comes in under the top of the cap. I agree it's simpler to replace the pressure cap with a flat one with a seal on it, and pressurise the expansion bottle!

Our old shared boat, Copperkins, ended up with a pressurised expansion tank and an overflow bottle. That worked, as the pressure cap made a good seal on the plastic neck f the expansion tank.

I am not quite sure of the problem you are highlihghting about coolant coming out of the top, but I found that the overflow container needs a small hole in the top to allow air to escape as the water flows in.

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The difference between volumetric expansion coefficients of water and steel is ~170x10^-6 / C

for an 80 degree increase in temperature water will expand by 0.0136

If you assume the gap above the water in the existing header tank is 1 kg (1 litre), for this to be taken up by water at 80C suggests you have 73 kg or 73 litres of water. I would say that is quite a lot and worst case scenario as the skin tank temperature should not increase by 80C.  In practise to expel 1 litre of water I would expect twice this quantity, nearer 150 litres / 85 pints / 10 gallons.

How big are skin tanks? A quick sum suggests mine might be a total 90 litres? I'm sure the expansion space in my Bowman is more than a couple of litres.

I'm left wondering if the skin tanks have been connected up in such a way to have air trapped which of course expands far more rapidly. A better (non leaking) radiator cap might mitigate the effect but I would check the position of pipes on skin tanks and loosen pipe clips to remove any potentially trapped air.

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On 26/05/2017 at 10:32, Mikexx said:

The difference between volumetric expansion coefficients of water and steel is ~170x10^-6 / C

for an 80 degree increase in temperature water will expand by 0.0136

If you assume the gap above the water in the existing header tank is 1 kg (1 litre), for this to be taken up by water at 80C suggests you have 73 kg or 73 litres of water. I would say that is quite a lot and worst case scenario as the skin tank temperature should not increase by 80C.  In practise to expel 1 litre of water I would expect twice this quantity, nearer 150 litres / 85 pints / 10 gallons.

How big are skin tanks? A quick sum suggests mine might be a total 90 litres? I'm sure the expansion space in my Bowman is more than a couple of litres.

I'm left wondering if the skin tanks have been connected up in such a way to have air trapped which of course expands far more rapidly. A better (non leaking) radiator cap might mitigate the effect but I would check the position of pipes on skin tanks and loosen pipe clips to remove any potentially trapped air.

 

I too have done similar calculations in the past an concluded the explanation for many engines needing a bigger expansion is there must be a significant amount of air or water vapour trapped in the coolant circuit. This expands considerably when the engine warms up leading to filling of the expansion tank.

I often wonder why the system needs to be sealed in the first place though. Why is a cap needed at all? Why not have a filling/expansion tank of five or ten litres capacity on the engine room wall like water-cooled vintage engines usually have?

I suppose the answer to my question is so the whole of the cooling system can be stuffed down underneath the deck boards out of sight.

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On 24/02/2006 at 20:07, Alec Gatherer said:

The pressure it's under is only 4lb/sq/in or 7 lb/sq/in, so no great problem with correct hose; most rubber auto hose will be fine.

I have an expansion tank from a Transit you can have if you want - save you £30 (unless you bump into me in a Joseph Holt's pub, in which case you will feel obliged to buy me a pint of Rough Mild @ £1-40)

 

An interesting illustration of how beer is rising in price at a rate way above inflation. 

If we assume 4% inflation per annum for the 11 years since 2006 when this comment was posted, a pint of rough mild ought to now cost £2.16.

It's a rare pint that costs less then three quid now and over £4 is commonplace around here.

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10 minutes ago, Mike the Boilerman said:

snip

I often wonder why the system needs to be sealed in the first place though. Why is a cap needed at all? Why not have a filling/expansion tank of five or ten litres capacity on the engine room wall like water-cooled vintage engines usually have?

I suppose the answer to my question is so the whole of the cooling system can be stuffed down underneath the deck boards out of sight.

First of all for canal use it is probably fine for engines to operate with an unpressurised system. They are pressurised because the base engines are very rarely marine engines and are usually some form of automotive unit.

The quest for greater power and more MPG has caused engines to run hotter than they used to and in fact certain parts like the exhaust valve seat and around the injector can have to displace so much heat when at high power their temperature at the water jacket side of the head  can rise to well over 100C and cause localised boiling. The body of the coolant remains at normal running temperature but if you get localised boiling first of all the steam formed will force coolant out of the system (I doubt that's happening in this case but your air/gas is a likely culprit) so the engine actually overheats. The other thing that happens is those parts that a locally boiling start to fur up so the conduct less heat into the coolant, this leads to even higher local temperatures that in turn causes things like cracking in the head.

To help mitigate the localised boiling the manufacturers pressurise the system to raise the boiling point of the coolant. Over the years I have  seen the pressure creep up from about 3psi via the more typical now 15psi to 21 psi on a particular diesel engine.

We certainly suffered localised boiling and subsequent cracked heads on 1.5s on the Thames when running them unpressurised unless we  removed the thermostats or fitted nothing more than a 62 degree one.

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Just to say that on my boat, with a large skin tank and Bowman heart exchanger, capacity about 35 litres, we just have the Bowman half full when cold. I hardly ever get any overflow into the jar that is under the overflow pipe. Has worked fine like that for 20 years, so I don't really see the need for a separate header tank, pressurised or not. 12psi pressure cap from memory (Mitsubishi 4 cyl).

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4 hours ago, Scholar Gypsy said:

Just to say that on my boat, with a large skin tank and Bowman heart exchanger, capacity about 35 litres, we just have the Bowman half full when cold. I hardly ever get any overflow into the jar that is under the overflow pipe. Has worked fine like that for 20 years, so I don't really see the need for a separate header tank, pressurised or not. 12psi pressure cap from memory (Mitsubishi 4 cyl).

You have to be a bit careful with extrapolating your experience to other boats and engines. I always say fill the header tank to full just once, run the engine well up to temperature and then let it cool. Whatever level the coolant  is then at is the correct level. This is in effect what you have done but I have been told about more than one Beta where the level drops so much air is allowed into the cooling system  and then into the skin tank. In those cases a separate header tank cured the problem.

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40 minutes ago, Tony Brooks said:

You have to be a bit careful with extrapolating your experience to other boats and engines. I always say fill the header tank to full just once, run the engine well up to temperature and then let it cool. Whatever level the coolant  is then at is the correct level. This is in effect what you have done but I have been told about more than one Beta where the level drops so much air is allowed into the cooling system  and then into the skin tank. In those cases a separate header tank cured the problem.

That's a very fair point, of course. I decided on my Easter trip that I really needed a hand-made dipstick, so I can measure the cold water level to the nearest mm (rather than just using the Mark 1 eyeball). It's on the to-do list. 

Oddly, my skin tank has no bleeding point ...

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28 minutes ago, Scholar Gypsy said:

Oddly, my skin tank has no bleeding point ...

As long as the top hose on the tank runs in a steady uphill with no kinks to the header tank/heat exchanger it should bleed itself. Its when there are kinks and loops/bends that air gets trapped

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1 hour ago, Tony Brooks said:

As long as the top hose on the tank runs in a steady uphill with no kinks to the header tank/heat exchanger it should bleed itself. Its when there are kinks and loops/bends that air gets trapped

Yes, that's exactly how mine is, with both the top and bottom hoses gently rising. The builder did say it was all a bit over-engineered. Here's the top hose removed so I can drain the skin tank.

dscf6862.jpg

 

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2 hours ago, Tony Brooks said:

As long as the top hose on the tank runs in a steady uphill with no kinks to the header tank/heat exchanger it should bleed itself. Its when there are kinks and loops/bends that air gets trapped

 

I thought skin tanks generally came in pairs?

In which case it would also depend how they are coupled.

There is also the angle of the skin tank from the horizontal given most boats are lower at the stern.

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1 minute ago, Tony Brooks said:

Agreed, unless the boat started life with an undersized skin tank and has had another added.

Some even have a horizontal skin tank under the engine.

 

Thanks, I live and learn. Mine has two on either side of the swim and thought this was common.

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