Adding An Expansion Tank To BMC 1800

[alan_fincher]

After putting it off for years I have decided I wish to modify the arrangements on Chalice's keel cooled BMC 1800 to include a proper pressurised expansion tank.

 

So I need to....

 

1) Change the pressure cap on the current header tank to one that just blanks the hole.

2) Pipe to a new plastic expansion tank.

3) Provide said tank

4) Ensure it has a 7.5 psi cap that is suitable.

 

But I can't find suitable parts.

 

There is a Barrus Shire bottle avaialble, but it's £40 from Midland and £43 at my local.

 

I might take the hit, but it has a 95 KPa cap on it, so is much higher pessure than I want, and it doesn't look "standard" to me to allow an easy change. Also the manager at my chandlery says if the caps are not fitted with great care, and lots of downward pressure, they chew up the plastic of the bottle neck, (so that's what you are paying £43 for! ).

 

Also no-one can help with a cap that blanks off where a standard BMC radiator cap might otherwise actually go.

 

Any ideas, please ?

 

(Note, I know it is possible to try an expansion tank that's not pressurised, based on cheaper methods, available from Heinz or Fairy Liquid. I've already decided I want to make the whole thing pressurised, so please concentrate just on solutions that will achieve that objective - thank you!)

[Guest]

After putting it off for years I have decided I wish to modify the arrangements on Chalice's keel cooled BMC 1800 to include a proper pressurised expansion tank.

 

So I need to....

 

1) Change the pressure cap on the current header tank to one that just blanks the hole.

2) Pipe to a new plastic expansion tank.

3) Provide said tank

4) Ensure it has a 7.5 psi cap that is suitable.

 

But I can't find suitable parts.

 

There is a Barrus Shire bottle avaialble, but it's £40 from Midland and £43 at my local.

 

I might take the hit, but it has a 95 KPa cap on it, so is much higher pessure than I want, and it doesn't look "standard" to me to allow an easy change. Also the manager at my chandlery says if the caps are not fitted with great care, and lots of downward pressure, they chew up the plastic of the bottle neck, (so that's what you are paying £43 for! ).

 

Also no-one can help with a cap that blanks off where a standard BMC radiator cap might otherwise actually go.

 

Any ideas, please ?

 

(Note, I know it is possible to try an expansion tank that's not pressurised, based on cheaper methods, available from Heinz or Fairy Liquid. I've already decided I want to make the whole thing pressurised, so please concentrate just on solutions that will achieve that objective - thank you!)

ASAP supplies used to stock this sort of thing.

 

http://www.asap-supplies.com/

Edited August 29, 2009 by Guest

[alan_fincher]

ASAP supplies used to stock this sort of thing.

 

http://www.asap-supplies.com/

Ah yes, you are right.

 

I did find that, and it's possible.....

 

Advantages

 

Cheaper

Accepts a 7psi cap they sell

 

Disadvantages

 

Not good for bulkhead mounting

19mm pipe not ideal for connecting to current header.

Possibly other open pipes to cap off, (though maybe they are sealed, and you drill them through if you need them ?).

 

But thanks for reminding me, 'cos when I looked the other day I missed it, for some reason.

 

I suspect a cap that fully blocks the top of the current tank is not going to be that easy to find. I'm not sure how smooth it is anyway TBH - I need to check again, I think!

[nb Innisfree]

You could source some supplers classic car spares, older cars, early '70s I think (Morris/Austin 1100/1300?) had this sort of arrangement

[alan_fincher]

You could source some supplers classic car spares, older cars, early '70s I think (Morris/Austin 1100/1300?) had this sort of arrangement

Yes, thanks....

 

I've spent some time looking at classic car parts, and on e-Bay. Very hard to tell if a particular tank is suitable, as it's not obvious what caps are used, how big, or how mounted.

 

We'll be scrapping a Fiesta in a few weeks, and I've even looked to see if the bottle can be "lifted" from there, (assuming I could lash up something to still deliver the car to the crusher, without it boiling).

 

However like most, it is bespoke to fit available space, and has an odd cap, and hangs on welded hooks in the engine bay that would be hard to mimic on the boat.

 

I will look again though, but was hoping someone would say "I've used one from a Mark 4 Cortina, and it works a treat", or something equally helpful!

 

I don't understand why a stout plastic bottle needs to cost £40 or more, (and many car ones do too....).

[LEO]

Hi,

 

A scrapyard would be the best bet - there is one - A G Evans Chesham Road Wigginton (close to Berko) which may help.

 

Leo.

[MoominPapa]

Alan, why are are you bothering? If it's to ensure that the current header tank is always full, it's just as easy to do that with an unpressursed expansion tank.

 

If your current header tank has a standard, bayonet "radiator cap" fitting, with a connection to the neck for an overflow hose, then just replace the cap with one which has 1) a seal on the cap which seals the cap to the top of the neck, and 2) has a lightly spring-loaded non-return valve in the centre which allows coolant _back_ inti the header tank as it cools. Such caps were standard fittings on cars for years before aerodynamics and pedestrian safety forced a move to low-profile crossflow radiators. They should be trivial to find.

 

With such a cap in place, run the pipe from the neck to a non-pressurised expansion bottle. Either connect the pipe to a fitting on the side of the bottle , or run it through the top but extend it almost to the bottom. Make sure the pipe joints are air-tight.

 

Now when the coolant expands and the pressure exceeds 7PSI the coolant will flow past the pressure-relief part of the cap into the neck of the header. From there it will flow down the pipe to the new expansion bottle. When the coolant contracts the partial vacuum will open the non-return valve in the centre and suck coolant back into the header via the neck and pipe. SImples!

 

You can check the level in your new expansion bottle without risking scalding too.

 

MP.

[Albion]

Yes, thanks....

 

I've spent some time looking at classic car parts, and on e-Bay. Very hard to tell if a particular tank is suitable, as it's not obvious what caps are used, how big, or how mounted.

 

We'll be scrapping a Fiesta in a few weeks, and I've even looked to see if the bottle can be "lifted" from there, (assuming I could lash up something to still deliver the car to the crusher, without it boiling).

 

However like most, it is bespoke to fit available space, and has an odd cap, and hangs on welded hooks in the engine bay that would be hard to mimic on the boat.

 

I will look again though, but was hoping someone would say "I've used one from a Mark 4 Cortina, and it works a treat", or something equally helpful!

 

I don't understand why a stout plastic bottle needs to cost £40 or more, (and many car ones do too....).

 

One from an Allegro would do everything that you want EXCEPT that with skin tank cooling you have a much greater range of expansion due to the greater volume of coolant. Your problem, sourcing from a vehicle, is that the coolant capacity is going to be much lower than a boat. In fact vehicles run the minimum quantity of coolant that they possibly can, consistent with adequate cooling in high ambient/heavily loaded conditions, because this gives a fast warm up, better fuel economy and a faster heater operation in winter.

 

If you kept the coolant level right at the bottom of the Allegro header then it MIGHT do what you require but only experimentation would prove it. I would have thought the tanks would be dirt cheap from a breaker if you can find one that still has an Allegro (or Maxi) in it.

Roger

[David Schweizer]

I am not sure why you want to add another expansion tank Alan. From the photos on the engine mount thread you already appear to have a perfectly adequate one. As long ast there is some water visible in the tank when the engine is cold the morning after a days cruising, you should be OK.

 

I know that some people like to see the header tank nice and full, but because of the volume of water in the system (keel tank and caorifier circuit) there will be significant expansion and that will just spew out into the bilges when the engine heats up. I did fit a non pressurised overflow tank on my header tank, but it never collects anything now that I do not keep on topping the header tank up, and there is always about an inch of water in the header tank in the morning.

 

Why make things more complicated than they need to be?

[alan_fincher]

One from an Allegro would do everything that you want EXCEPT that with skin tank cooling you have a much greater range of expansion due to the greater volume of coolant.

Yes, you have a point.

 

Part of the problem I'm trying to solve is that the current engine mounted cast header tank (Calcutt) has to be left so empty to stop water being expelled when everything is hot, that you risk letting it run too low, (as happened, I think, with dramatic effect on the last day of a 3 week trip).

 

Having added a calorifier, I have obviously increased the volume of water that can expand a tad further, though I assumed not by much, as calorifier coil has low volume compared to skin tank!.

 

You are correct, if I now fully fill the existing header tank, and allow any air space to be in the expansion bottle, then that must have more total capacity than the empty space at the top of my current tank, or I'll just move the overflowing problem up a level.

 

I'm now doubtful that even the Shire bottle I have seen will handle the current degree of expansion.

 

You may just have saved me a silly mistake, but I now agree, no car one is likely to have the capacity.

 

Perhaps I'll go the MP route after all, at least as a first try - it certainly looks like the cheaper experiment.

 

Thanks all - the power of sensible forum advice (again!)

 

Need to get a sheared engine mount bolt out first, before I can try it, though.

 

 

 

 

I am not sure why you want to add another expansion tank Alan. From the photos on the engine mount thread you already appear to have a perfectly adequate one. As long ast there is some water visible in the tank when the engine is cold the morning after a days cruising, you should be OK.

 

I know that some people like to see the header tank nice and full, but because of the volume of water in the system (keel tank and caorifier circuit) there will be significant expansion and that will just spew out into the bilges when the engine heats up. I did fit a non pressurised overflow tank on my header tank, but it never collects anything now that I do not keep on topping the header tank up, and there is always about an inch of water in the header tank in the morning.

 

Why make things more complicated than they need to be?

David,

 

I checked our coolant before setting off on our final day's holiday. It looked OK, i.e. low down, but definitely present, as I always run it, by experience.

 

We started off at the foot of Three Locks, but shortly after leaving the top, the engine boiled.

 

After some investigation, I could find no cause, replenished the water, (lots!), and carried on. It got us home fine, (to Cow Roast), and there seems to be no enduring problem or damage.

 

I can only assume that the level mine needs to be consistent with not expelling anything, and not ceasing to circulate, has to be more precise than I care to live with.

 

I'd rather not dissapear in clouds of steam again, (could have happened in Harecastle!), so am investigating ways of avoiding. Obviously for the same BMC engine, whether this is a problem or not depends on a number of factors. I have both added a calorifier, (marginal increase in total volume), but also moved from a 74 degree to 82 degree stat, so the expansion of my fixed volume of coolant will also have increased.

 

I believe I am on the margin of what the engines own tank can achieve, but it's not impossible there is a small coolant leak somewhere in the circuit that I have not yet found. Hoses that are clamped tight with worm-drive clips at one inspection do seem to have a habit of having loosened by the next, and the system is under pressure, of course.

[Yoda]

I think your head gasket is on its way out. My experience in cars with your description, leads me to suggest this. Its not fully gone yet, may I suggest a service.

[nb Innisfree]

Alan, why are are you bothering? If it's to ensure that the current header tank is always full, it's just as easy to do that with an unpressursed expansion tank.

 

If your current header tank has a standard, bayonet "radiator cap" fitting, with a connection to the neck for an overflow hose, then just replace the cap with one which has 1) a seal on the cap which seals the cap to the top of the neck, and 2) has a lightly spring-loaded non-return valve in the centre which allows coolant _back_ inti the header tank as it cools. Such caps were standard fittings on cars for years before aerodynamics and pedestrian safety forced a move to low-profile crossflow radiators. They should be trivial to find.

 

With such a cap in place, run the pipe from the neck to a non-pressurised expansion bottle. Either connect the pipe to a fitting on the side of the bottle , or run it through the top but extend it almost to the bottom. Make sure the pipe joints are air-tight.

 

Now when the coolant expands and the pressure exceeds 7PSI the coolant will flow past the pressure-relief part of the cap into the neck of the header. From there it will flow down the pipe to the new expansion bottle. When the coolant contracts the partial vacuum will open the non-return valve in the centre and suck coolant back into the header via the neck and pipe. SImples!

 

You can check the level in your new expansion bottle without risking scalding too.

 

MP.

 

Edited due to incompetence yet again

Edited August 29, 2009 by nb Innisfree

[nb Innisfree]

I think you will have approx 80 lt capacity (assuming 50 lt cal) which should expand by 1.5 to 2 lt

[david and julie]

But I can't find suitable parts.

Its a fair ammount of reading, but there's lots of useful gear on this site.

http://www.nfauto.co.uk/download/catalogue.pdf

[alan_fincher]

I think you will have approx 80 lt capacity (assuming 50 lt cal) which should expand by 1.5 to 2 lt

I think you are talking about the hot water capacity of my calorifier, (actually a nominal 55 litres).

 

Surely that's not relevant in considering expansion of the engine coolant, which, as far as the calorifier goes, is just in one of the coils, so a pint or two at most, I'd have thought, (hopefully, or I'd be bathing in anti-freeze.....).

 

 

I think your head gasket is on its way out. My experience in cars with your description, leads me to suggest this.

On what basis ?

 

There is certainly no evidence of water in the oil, or oil in the water, but I'm not saying it's not possible......

[alan_fincher]

Its a fair ammount of reading, but there's lots of useful gear on this site.

http://www.nfauto.co.uk/download/catalogue.pdf

Thanks,

 

I've not seen that.

 

I'm not sure there is a suitable bottle or tank in there at affordable cost if I wanted to stick with a pressurise solution, but it does seem to be a source of a blanking radiator cap with none of the pressure relief innards which I'd need to put on the existing header.

 

Useful info - appreciated.

[nb Innisfree]

I think you are talking about the hot water capacity of my calorifier, (actually a nominal 55 litres).

 

Surely that's not relevant in considering expansion of the engine coolant, which, as far as the calorifier goes, is just in one of the coils, so a pint or two at most, I'd have thought, (hopefully, or I'd be bathing in anti-freeze.....).

 

Sorry another complete cock up on my part, what I should have said was approx 30 lt of coolant with half a litre of expansion.as you say about a pint

[NB Alnwick]

I think your head gasket is on its way out. My experience in cars with your description, leads me to suggest this. Its not fully gone yet, may I suggest a service.

 

Alan you should probably consider this possibility - early signs of head gasket failure include gas (rather than oil or fuel) in the coolant causing it to expand and appear to boil excessivly. Another early sign is excessive vibration because one or more cylinders will have to do more work than the ones that are losing compression and this may be the cause of your broken engine mount stud. If I were in your position I would be open to all possibilities. Perhaps this Winter will be a good time to take the engine out and give it full overhaul?

Edited August 30, 2009 by NB Alnwick

[alan_fincher]

I am starting to wonder, although in several years, and many thousands of miles it's our only overheating incident, (since an inadequate skin tank got scrapped, and a bigger one built externally).

 

By that, I mean the gauge doesn't even go high, let alone any consideration of boiling. If it's head gasket, I'm kind of surprised by just the one incident, but it could just be starting to worsen, I guess.

 

On the day in question it was marginal whether to top the header tank up or not, but I judged it to be no lower than the previous morning, so decided not to. It's possible it had gone down, as I don't measure it with any precision.

 

I suspect we could actually have a slow leak on the cooling system. There is a shallow area on the baseplate, with the remnants of three sides of the old skin tank just burnt off, but not ground away. This area, which is under one of the connections to the new skin tank, seems to get some "water" in it. I think it is possible that either something at the point where the hose joins the skin tank leaks, (there are reducers and compression fittings involved), or that water could be running down the hose from the engine end.

 

The "do I, dont't I, get it taken to bits" debate is a difficult one. I can't help feeling bits of the engine might benefit from a strip down and assessment, but equally many "in the know" advise the "if it ain't broke, then don't fix it" approach. I'm by no means convinced it's "broke", (other than that ruddy bolt, which may, or may not be, unconnected).

[NB Alnwick]

I have never been a great fan of the "if it ain't broke, then don't fix it" approach. Maintenance should be periodical and preventative - your engine may be telling you that it needs an overhaul. Better to embark on your next cruise with a reliable recently overhauled engine than one that might go 'pop' in the middle of nowhere and spoil your holiday . . .

[alan_fincher]

I have never been a great fan of the "if it ain't broke, then don't fix it" approach. Maintenance should be periodical and preventative - your engine may be telling you that it needs an overhaul. Better to embark on your next cruise with a reliable recently overhauled engine than one that might go 'pop' in the middle of nowhere and spoil your holiday . . .

Yes, I can't argue with that, but of course another consideration is how much have you got to spend on your boating.

 

Unfortunately I can see us getting priced off the canals, maybe sooner rather than later.

 

I realise some rebuilding now might avoid a worse bill later, but some of it is about assessing likely problem, likely risk, and what speculative spend is worthwhile to try and have a smoother life. I'm not that confident to start going inside the engine myself, TBH - too many years since I last did, and I don't have the experience, so we are talking quite a lot of spend.

 

Part of the problem is finding the right man, particularly if boat can't move long distances. Some people don't seem overly keen to get involved, and it is doubtful if some others who work "mobile" have the facilities to lift an engine out for more major work.

 

I have already been investigating some options though, even before recent overheating or broken bolt incidents.

 

It doesn't seem unreasonable to see if I can modify the cooling circuit so there is always more coolant in the system, and then see if it repeats the boiling. I may just have been negligent, and head gasket could easily be a red herring, (it was the last time people suggested it was the likely problem - actual issue was inadequate skin tank on the boat).

[Guest]

This may be of little use to you but:

Ihave just been helping my mate with his BMC engine (starter knackered). Whilst in the egine hole I took notice of his cooling system. It appears to be a blanking cap on the heat exchanger, and a plastic expansion boltte with a pressure cap. I was surprised how small the plastic bottle is. He has owned the boat for nine years, and to the best of my knowledge has had no cooling problems.

[alan_fincher]

This may be of little use to you but:

Ihave just been helping my mate with his BMC engine (starter knackered). Whilst in the egine hole I took notice of his cooling system. It appears to be a blanking cap on the heat exchanger, and a plastic expansion boltte with a pressure cap. I was surprised how small the plastic bottle is. He has owned the boat for nine years, and to the best of my knowledge has had no cooling problems.

Well, (subject to getting the engine back on proper mounts), I don't see why I couldn't....

 

1) Fill the header tank completely

2) Pipe the overflow into a very generous but temporary container.

3) Take it for a (non-manic !!) "thrash" .

4) Measure what has got pushed out.

 

Its probably easier to do a practical test than to try and estimate water capacity of entire system then do the science around how much water expands, (plus I get to take the boat out! )

 

Having initially assumed an all pressurised solution would be best, I think I'm now drawn towards MP's suggestion to keep the pressure cap on the engine, and make all the "overflow" side unpressurised.

 

Thanks for the heads up on your friends system though - I hope it doesn't just mean he has a marginal skin tank sizing!

[Guest]

Well, (subject to getting the engine back on proper mounts), I don't see why I couldn't....

 

1) Fill the header tank completely

2) Pipe the overflow into a very generous but temporary container.

3) Take it for a (non-manic !!) "thrash" .

4) Measure what has got pushed out.

 

Its probably easier to do a practical test than to try and estimate water capacity of entire system then do the science around how much water expands, (plus I get to take the boat out! )

 

Having initially assumed an all pressurised solution would be best, I think I'm now drawn towards MP's suggestion to keep the pressure cap on the engine, and make all the "overflow" side unpressurised.

 

Thanks for the heads up on your friends system though - I hope it doesn't just mean he has a marginal skin tank sizing!

Thats always a possibility! Think he would know by now though.

[alan_fincher]

Thats always a possibility! Think he would know by now though.

It's probably only reckless speeders like me that actually ever boil over!

 

Although I can't say we had had too much opportunity to speed up Soulbury Three Locks, thinking back.