Expansion Tank for BMC Engine

[Baron & Mrs Boater]

I have had my annual RCR engine inspection today, and the engineer suggested I fit an expansion tank to the cooling system on my BMC engine. Has anyone fitted one - what did you use - shall I go and get one off a scrap car, or is it just not necessary ?

[Guest]

I have had my annual RCR engine inspection today, and the engineer suggested I fit an expansion tank to the cooling system on my BMC engine. Has anyone fitted one - what did you use - shall I go and get one off a scrap car, or is it just not necessary ?

Coolant has to expand to somewhere when hot. Does it find its way into the bilges at present?

[alan_fincher]

I have had my annual RCR engine inspection today, and the engineer suggested I fit an expansion tank to the cooling system on my BMC engine. Has anyone fitted one - what did you use - shall I go and get one off a scrap car, or is it just not necessary ?

It may depend upon what the engine has on it already, (and also on the volume of coolant your skin tank holds).....

 

If it's been marinised like the one here....

 

Link to Marinised BMC Engine

 

then my understanding is that the biggish tank on top is actually designed to act as an expansion tank, and that no additional one is considered necessary.

 

It should contain enough water when cold that water flows freely round the whole circuit, but (my understanding again) will probably be less than half full, with the remaining space supposed to be sufficient for expansion.

 

Filled too full, it will push coolant out the pressure cap, when it gets hot, (thereby wasting antifreeze by pushing it out with the water).

 

My boat has a marinised BMC 1800, and previously had a very poorly designed skin tank, that was much too "thick" so contained far more water than ideal. Previously because of the expansion of more water than sensible, it was hard to get the level in the tank right, such that nothing got ejected.

 

But our replacement skin tank, (1" thick, rather than 4" thick, even though it presents about twice the cooling area to the swim), probably contans less than half as much water.

 

Now the "air space" in the standard header tank on the engine more than copes with expansion, with no coolant loss. Whereas I was considering fitting a separate expansion bottle previously, I can now see I don't need to.

 

Alan

[John Orentas]

Assuming your chap means an expansion / header tank with a pressure cap on the top. You could go the scrap-yard route, make, or buy one, many cars have remote plastic ones. Whatever you do, try and get one with a large diameter pipe connecting it to the engine (more than 3/4 inch diameter). Small pipes are reluctant to allow air bubble's to pass through and out of the engine.

 

I once made that mistake with my first boat, a large amount of air from the keel tank passed up into the engine but could not progress further. An engine full of air, it did some damage before I found the problem.

Edited February 24, 2006 by John Orentas

[Baron & Mrs Boater]

we are losing coolant through the overflow on top of the engine, when we are running hot - which is a nuisance as it collects under the engine, and also potentially damaging should we run out, so I guess if I fitted a tank at least I could see the levels were right. That said, I presume I need some sort of pressure resistant tubing - if I am getting a tank with a pressure cap ?

[Guest]

we are losing coolant through the overflow on top of the engine, when we are running hot - which is a nuisance as it collects under the engine, and also potentially damaging should we run out, so I guess if I fitted a tank at least I could see the levels were right. That said, I presume I need some sort of pressure resistant tubing - if I am getting a tank with a pressure cap ?

 

You will get an idea here, look under expansion tanks:

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

[Alec Gatherer]

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)

[Baron & Mrs Boater]

Its a useful site - thanks !

[alan_fincher]

we are losing coolant through the overflow on top of the engine, when we are running hot - which is a nuisance as it collects under the engine, and also potentially damaging should we run out, so I guess if I fitted a tank at least I could see the levels were right. That said, I presume I need some sort of pressure resistant tubing - if I am getting a tank with a pressure cap ?

Does your BMC already have a tank on top of it similar to the one on the Calcutt web page I linked to ?

 

How big is your skin tank, (in all directions ?).

 

If you do go for an overflow bottle, I think there are two potential ways of doing it.....

 

1) Keep current "radiator cap", but arrange that any water ejected through the pipe on the side of the radiator cap is passed by a hose into a NON-pressurised container, slightly higher than the current tank. The problem though, is that this may not run back automatically as the engine cools. (But if you take the cap off when it has cooled, there should be space for it to run back into the engine).

 

2) Use a pressurised bottle, (as John suggests these should be easy to get from an automotive application - i.e. a breakers yard). I believe you must then use an alternate cap on top of the engine that simply blanks off the current hole. Your correctly rater pressure cap would then go instead on the expansion bottle, such that the whole lot becomes pressurised. This is probably the better arrangement, but does mean that if you put enough coolant in to completely fill the current tank and some of the new tank, and then remove the blanking plate from the current cap location, any excess water in the new bottle may be lost.

 

Others may have a different view here, but, as I said in my original post, if you talk to someone like Calcutt, they will say that the engine mounted tank should be able to cope with all normally expected expansion.

 

Are you sure you are simply not overfilling it, so not leaving enough air-space at the top. Calcutt said that when cold, the engine mounted tank should probably appear less than half full...... This doesn't "feel" right, but that's how ours now is, and works fine.

 

Alan

[Baron & Mrs Boater]

Alan,

 

I do have a Bowman heat exchanger unit on the top, which always seem to be nearly empty, though it doesnt appear to be leaking from anywhere, other than the overflow when hot. The engineer did say I needed to cap it off, and use a tank off a scrap car with the radiator cap - but I've never seen one on another boat !

 

The skin tank dimensions, well I am not too sure, but it seems to run down the length of the swim.

[alan_fincher]

Alan,

 

I do have a Bowman heat exchanger unit on the top, which always seem to be nearly empty, though it doesnt appear to be leaking from anywhere, other than the overflow when hot. The engineer did say I needed to cap it off, and use a tank off a scrap car with the radiator cap - but I've never seen one on another boat !

 

The skin tank dimensions, well I am not too sure, but it seems to run down the length of the swim.

So that's my "option 2", then. I've certainly seen this on other boats. Your current pressure cap may be a different style to that on any expansion bottle you end up acquiring. If so, you will need to also get hold of a cap that fits your new bottle, with the same opening pressure rating as marked on your current cap. (From memory my BMC 1800 opens at 7lbs, but that's only from memory...)

 

Worth knowing how big your skin tank is though, (by far the largest thing contributing to how much coolant you have in total). I suspect your's is going to be quite large, (and probably quite "thick"), as it sounds like you have a hell of a lot of expansion. If it is, the extra bottle may well be the only way to ensure no coolant is getting pushed into the bilges.

 

I'm out of ideas - over to others, I think!....

[Baron & Mrs Boater]

Thanks for your input - I will mull it over !

[Baron & Mrs Boater]

Here's a thought - if the existing cap on the heat exchanger is US, could it be letting water out through the overflow by contracting when it shouldn't ?

 

Maybe I just need a new cap ?

[alan_fincher]

Here's a thought - if the existing cap on the heat exchanger is US, could it be letting water out through the overflow by contracting when it shouldn't ?

 

Maybe I just need a new cap ?

Has it done this ever since you got the boat, or is it a new "feature" ?

[Baron & Mrs Boater]

It's done it since we bought the boat ~ but that is only 9 months. The cap is a bit loose.

[Cafnod]

Hi Baron & Mrs. B

My first thought would be to check with Calcutt that there is the correct amount of water in the heat exchanger, are there not any marks to verify this?

Having done this if the problem persists I would then change the cap, go to a decent motor factors (not Halfords) and say "One of these please." For the sake of a couple of quid it may be the answer.

If it is still occuring my next step would be to pressure test the cooling system to see if excessive pressurisation of the coolant is occuring, which may happen for a number of reasons.

 

Hope this helps

 

Regards

 

Cafnod

[Baron & Mrs Boater]

I think I will try the new cap first, I will let you know if it sorts it out. The heat exchanger has no marks on it, in fact you can't really see the water level in it because of the fins in it - I stuck a pencil down it as a dipstick.

[Cafnod]

I wonder if there was an original fit cap with a dipstick type extension on it or something similar to ascertain correct water level, Calcutt (who I assume marinised this BMC?) are a reputable company, I cannot imagine that they expect people to guess or use pencils.

I think change the cap and make a phone call to Calcutt. If it cures the problem you wll have enough change out of a fiver for a pint of beer.

[alan_fincher]

I'd usually be the first to knock Halfords, but I actually think you are as likely to find the right radiator cap there as easily as anywhere else.

 

Look in their index book for ones to go on things like Sherpa vans, (or even MGBs). You need to match the pressure though - should be stamped on current one, and may be less than in some automotive applications. If it's a very low pressure you may need to go to someone like Calcutt, as a motor car place may not have it.

 

Personally I doubt this will sort it, but as Cafnod says, for just a couple of quid or so you can at least rule it out.

 

But to me it sounds like an issue with the water level rising too high, rather than either excess pressure in the system, or too little pressure in the system. This could be expansion of "too much" water, or possibly bubbles trapped in the system somewhere, pushing water out.

 

Do try the cap, but if it's always done it, (since you had the boat), and still does, I'd also look at how much water you actually have in the total system..... 1" thick skin tank implies there will probably be enough designed in space in your existing header tank. But 4" thick skin tank implies 4 times as much water for same useful area of skin tank, and hence a hell of a lot of expansion space required.

 

Please at least rule this out for me - it should be easy enough to see if it's "thick" or "thin", (unless it's on the outside of the swim, as our new one now is!....).

[David Schweizer]

Baron

 

I had exactly the same problem with my BMC 1.5. and am listing below how I solved it. (I realise that some of this has already been suggested, but hope that putting it all together will help.

 

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)

 

3. Finally there is no dip stick for the header tank, but as a rule of thumb the coolant level should be about half an inch above the core tube and about an inch from the bottom of the filler neck (sorry about the non metric measurements) Put any more in and as already suggested it will just pee out of the overflow pipe as soon as the engine warms up and be wasted.

 

Hope that helps

Edited February 25, 2006 by David Schweizer

[Cafnod]

Hi again B & B

In case you dont know Partco are the main stockists of Quinton Hazell parts. You will find a Partco, Express, Apex or other large motor factors somewhere near your home or mooring. The reason I recomended these rather than a high street shop like Halfords is that they will look at the part rather than start saying "What is this off we need an engines number, we dont sell parts for boats" etc etc ad nauseum.

Best of luck, hope to hear problem solved within the next few days.

 

Cafnod

Edited February 25, 2006 by Cafnod

[dor]

Welcome Back David!!

 

 

Expansion tank: The pressure cap needs to be right, we've acertained that. Also you need to know what is the correct levle.

 

I spent ages trying to find the leak in my system (Thorneycroft) as that used t o push water out. In the end I decided I was just filling it up too much and settled for a lower water levle which is fine.

Edited February 25, 2006 by dor

[Baron & Mrs Boater]

Baron

 

I had exactly the same problem with my BMC 1.5. and am listing below how I solved it. (I realise that some of this has already been suggested, but hope that putting it all together will help.

 

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)

 

3. Finally there is no dip stick for the header tank, but as a rule of thumb the coolant level should be about half an inch above the core tube and about an inch from the bottom of the filler neck (sorry about the non metric measurements) Put any more in and as already suggested it will just pee out of the overflow pipe as soon as the engine warms up and be wasted.

 

Hope that helps

 

 

Many thanks David.

[Guest]

Welcome Back David!!

Expansion tank: The pressure cap needs to be right, we've acertained that. Also you need to know what is the correct levle.

 

I spent ages trying to find the leak in my system (Thorneycroft) as that used t o push water out. In the end I decided I was just filling it up too much and settled for a lower water levle which is fine.

My findings with a Vetus.

[leechy]

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