Jump to content
Strawberry Orange Banana Lime Leaf Slate Sky Blueberry Grape Watermelon Chocolate Marble
Strawberry Orange Banana Lime Leaf Slate Sky Blueberry Grape Watermelon Chocolate Marble
Peter Thornton

Losing water

Featured Posts

We have just had a header tank fitted to our BMC 1.8. 

Before this we didn't seem to be using any water. Since fitting the tank we are losing about 1/2 pint each day. We even lose water when the boat is just on the bank without the engine running.

i can't see where the water is going.

I wonder whether we had an air lock in our skin tank and whether having a header tank higher in the system than before is gradually filling this up - in which case I guess it will eventually stop.

Any thoughts would be appreciated!

Share this post


Link to post
Share on other sites

Hot water expands, so your loss is probably the water contracting into the engine when it cools, assuming of course that you are certain there are no leaks.

Share this post


Link to post
Share on other sites

Not sure I follow that? The header tank is topped up to the mark when cold then the level rises when the engine gets warm. The level doesn't get to the overflow then settles down when cooling - but to below the original mark.

Share this post


Link to post
Share on other sites

In that case, as you are checking andtippingbup when cold, it could be air trapped In the system.

The skin tank usually has a bleed point (often a bolt) on its top surface.

The other common trap for air is if you have a horizontal clarified. Air gets trapped in The could and can be a out to bleed.

Share this post


Link to post
Share on other sites

Can I just be clear that when you say you have had a header tank fitted, you mean an additional separate bottle, different from the "header tank" on the engine that you presumably had before this modification.

If so exactly what is the new bottle connected to, and what has been done about pressure cap(s)?

Has the one on the engine been replaced with just a blanking type, and the cap is now on the new bottle, (so the bottle is part of the pressurised system).

Or is the pressure cap still on the engine tank, leaving thee bottle vented, and not under pressure?

Pictures would be good!

EDIT:

And sorry, I have to ask......

If you were not losing any water before, why have you made this modification, please?  (I thought people only bothered when they were losing water!).

Edited by alan_fincher

Share this post


Link to post
Share on other sites

Thanks Alan

Firstly, we fitted the header tank (or more accurately had it fitted by the boatyard) because we had been concerned that it was quite difficult for owners to correctly judge the proper level to top up to. One of our previous engineers had suggested that it could be overfilled with dire consequences and I felt that this could lead to underfilling. We have had a couple of unexplained overheating episodes.

The header tank has a pressure cap on it and the feed goes to the engine and to the collar below the pressure cap. So, yes, the header tank is part of the pressurised system. I've watched it whilst the engine warms up and the level gradually rises as the engine warms up.

It's all been fitted professionally and looks good. I've tried to see if there is any leak from the tank but it's difficult as the locker it's in does get damp from the rain. If we have a dry spell then I'll try again.

Finally, we are in the middle of a 5 week cruise which is why I've not consulted the boatyard that fitted it. 

If it is gradually getting rid of air locks in the system then I guess it won't go on forever.

 

Edited by Peter Thornton

Share this post


Link to post
Share on other sites

So has the pressure cap that would have been on the original engine mounted tank been changed to one that just acts as a blanking plate?

Or is there any chance there are now two pressure caps - the original one on the engine tank, and a new one on the new tank?

Share this post


Link to post
Share on other sites
6 minutes ago, Peter Thornton said:

There are two pressure caps, the original one and one on the header tank.

Do you know the pressure rating of each?

(This might all be a red herring, I'll admit, but depending on the opening pressure of each cap, I can see a number of different scenarios as to exactly what might happen as it heats up and cools down again.)

How much coolant is apparently "missing" each time it does cool down again?

As you say, I guess it could just be air working its way out, but did they actually drain coolant out and replace it?  If not, why would air have got in there?

Share this post


Link to post
Share on other sites
Not sure of the ratings, but I'm pretty sure it's not getting hot enough to blow off. The temp gauge sticks at 80 when it's warmed up.
It's about half a pint or so but the really puzzling thing is that it loses water even on days when we don't run the engine.

Share this post


Link to post
Share on other sites

Unless I'm misunderstanding you, surely at least the pressure cap on the engine has to be opening and passing water, otherwise the level in the new external botte wouldn't increase.

Half a pint sounds a lot, and I can't see it can be trapped air bleeding out if it still does it without running the engine.

I don't think you have answered the question about whether coolant was drained from the engine when this modification was made.  I think it's relevant, because if "yes" air could have got in, but if "no" I can't see why it would have done.

Share this post


Link to post
Share on other sites

I need to have a good look at it but I think the flexible pipe is connected to the collar below rhe pressure cap.

No idea whether the coolant was drained, its possible.

 

Share this post


Link to post
Share on other sites
1 hour ago, Peter Thornton said:

There are two pressure caps, the original one and one on the header tank.

That's probably the problem. Most pressure caps have an inner  seal that rests on the inside of the cap orifice, and have a metal to metal seal on the outer lip. This is OK for letting water out, as it will (usually!) go through the overflow pipe. However, when the engine cools down, air can be drawn in from around the rim, as well as through the overflow pipe. With a separate header tank, water can also flow through the lip "seal", evaporating from the top of the heat exchanger. Clue may be rust marks around the pressure cap.

When we added a header tank to Copperkins, we changed the heat exchanger pressure cap to a flat, non vented cap with a rubber seal. An alternative is to change the pressure cap for one with a rubber seal around the lip, in which case the cap on the new header tank could be left off, or slack.

Share this post


Link to post
Share on other sites
3 minutes ago, Iain_S said:

That's probably the problem. Most pressure caps have an inner  seal that rests on the inside of the cap orifice, and have a metal to metal seal on the outer lip. This is OK for letting water out, as it will (usually!) go through the overflow pipe. However, when the engine cools down, air can be drawn in from around the rim, as well as through the overflow pipe. With a separate header tank, water can also flow through the lip "seal", evaporating from the top of the heat exchanger. Clue may be rust marks around the pressure cap.

When we added a header tank to Copperkins, we changed the heat exchanger pressure cap to a flat, non vented cap with a rubber seal. An alternative is to change the pressure cap for one with a rubber seal around the lip, in which case the cap on the new header tank could be left off, or slack.


Yes,

If you are going to make the extra tank pressurised, then simply from the physics, to me the original pressure cap needs to be replaced with a blanking cap that will allow coolant to flow at all times unrestricted (in both directions) through the original overflow, to which the new "extension" tank is now connected.

It seems to me that if the whole lot is pressurised, relying on just metal to metal contact to form a seal at the lip of the old tank isn't going to guarantee nothing gets out at that point.

However this would imply it should be possible to see coolant escaping at that point, and if Peter is saying it loses coolant even when not run, you might reasonably expect a puddle somewhere,

However, intuitively to me you shouldn't have two pressure caps, particularly as they are fairly imprecise things, and maybe the two are interacting in an "unhelpful" way.

Replacing what's on the engine with something like this might improve things, but it really depends exactly what they have chosen to do.


https://www.asap-supplies.com/engine-spares-gearboxes/pressure-caps/pressure-cap-header-tank-blanking-plug-206900

Share this post


Link to post
Share on other sites
10 hours ago, Iain_S said:

That's probably the problem. Most pressure caps have an inner  seal that rests on the inside of the cap orifice, and have a metal to metal seal on the outer lip. This is OK for letting water out, as it will (usually!) go through the overflow pipe. However, when the engine cools down, air can be drawn in from around the rim, as well as through the overflow pipe. With a separate header tank, water can also flow through the lip "seal", evaporating from the top of the heat exchanger. Clue may be rust marks around the pressure cap.

When we added a header tank to Copperkins, we changed the heat exchanger pressure cap to a flat, non vented cap with a rubber seal. An alternative is to change the pressure cap for one with a rubber seal around the lip, in which case the cap on the new header tank could be left off, or slack.

Indeed,  when we had a share in Honeystreet it had the same arrangement.  A flat, non-venter cap, with wire wrapped around it to stop you removing it,  and a vented cap on the expansion tank.

Edited by cuthound
To unmangle the effects of autocorrect.

Share this post


Link to post
Share on other sites

Thanks for all your help folks, I've looked at it again this morning and I think the cap on the engine is indeed a blanking cap rather than a pressure cap. It looks just like the one in Alan's link and has a black rubber pip in the middle of it.

No surprise really I suppose as our boatyard does do a good job, it was just my ignorance that assumed it was the original pressure cap.

Still, the mystery is as to why we are topping up with water to a much greater extent than before the tank was fitted.

Thoughts:

1. Co-incidence. I don't buy that one really.

2. Leaks in the new pipe work or tank

3. Leak exposed by the fact that we now have a coolant reservoir sitting higher than previously.

4. As in 3 but now filling previously up filled air locks. In which case it will stop at some point.

I'll keep looking and report back when it's solved!

 

 

Share this post


Link to post
Share on other sites

I don't think just a small increase in the head because of a raised tank is likely in itself to cause something to leak that did not previously do so.

Has the original pressure cap been reused on the new bottle, or is it a new one?  If the latter is the rating the same as the original.  I don't think on a BMC it is sensible to have above 7 psi, and less is probably preferable if you have a Bowman or Polar header tank with those domed rubber end caps. (Towards the end of my ownership of a boat with a BMC 1800, I replaced the cap with one of just 4 psi).

Increasing the operating pressure could, I guess, cause leaks not present with a lower pressure cap.

However none of this explains you having said the level still drops even if the engine is not run.  That implies it is happening when it is not under pressure at all.

Does it lose a set amount of water, then stabilise, or if you leave it longer does it continue to fall?  Is there a point at which it stops falling?

Share this post


Link to post
Share on other sites
On 25/09/2017 at 11:42, alan_fincher said:

However none of this explains you having said the level still drops even if the engine is not run.  That implies it is happening when it is not under pressure at all.

 

If the OP can keep adding half a pint daily without it ever appearing in the bilges or in the oil in the sump, this points to an internal leak across the Bowman heat exchanger. Regardless of the reason for the leak developing, I can think of no other explanation for the loss. 

Water is passing through the leak from the sealed system into the raw water circuit and out into the cut, I suspect.

Share this post


Link to post
Share on other sites
10 minutes ago, Mike the Boilerman said:

 

If the OP can keep adding half a pint daily without it ever appearing in the bilges or in the oil in the sump, this points to an internal leak across the Bowman heat exchanger. Regardless of the reason for the leak developing, I can think of no other explanation for the loss. 

Water is passing through the leak from the sealed system into the raw water circuit and out into the cut, I suspect.

The OP says he has a skin tank in the first post of this thread, so no raw water cooling.

Edited by cuthound
Phat Phingers

Share this post


Link to post
Share on other sites
On 25/09/2017 at 12:55, cuthound said:

The OP says he has a skin tank in the first post of this thread, so no raw water cooling.

You're right!

How odd. I was sure I'd seen a Bowman heat exchanger mentioned earlier in the thread.

Share this post


Link to post
Share on other sites
2 hours ago, Peter Thornton said:

Cruising at the moment but it does have a skin tank and a Bowman exchanger. Not sure if it is now one sealed system, will post some pictures later.

If it has a skin tank it will have a Bowman, Polar, JG Meakes or home fabricated EXHAUST MANIFOLD that may or may not contain a heat exchanger. As you say Bowman then its probably a Bowman manifold that can have a heat exchanger core fitted. If it has two large (including the outlet from the thermostat housing) hoses and no others then its keel or tank cooled. If it has another two smaller hoses then its heat exchanger cooled but it will then have an extra brass belt driven water pump fitted to the engine.

It is always possible but unlikely that some clown has fed the raw water circuit of a heat exchanger cooled engine into the skin tank to cool it but then two header tanks would be required, one for the engine (like you have) and a totally separate one for the skin tank circuit.

People just assume that when they see Bowman its a heat exchanger without inspecting the plumbing.

Share this post


Link to post
Share on other sites

Thanks Tony.

this is an ex Ownerships boat of 1997 vintage. I think it started off with using raw canal water to cool and then was converted whilst part of Ownerships, along with all of the other boats. (I stand to be corrected!)

I don't know if the pictures help?

interestingly, today's cruise resulted in the header tank filling right up and then dripping out. The engine was working reasonably hard in a shallowish canal (Leeds Liverpool beyond Silsden) but no signs of overheating and the gauge on its normal 80. No signs of boiling or anything like that, the level just rose to the top of the tank and then dripped. So I'm wondering if the air pockets might have been filled and this is the result? The header is filled to the Min mark, about 1/4 full.

Tony, if it's cooled directly from the skin tank then is it all one system and is the header tank effectively connected directly to the skin tank?

i feel I'm learning a lot more than I expected this week! Thanks to all the tutors ......

FullSizeRender.jpg

IMG_3808.JPG

IMG_3809.JPG

IMG_3811.JPG

Share this post


Link to post
Share on other sites

I've had shares in Ownerships boats built in 1992 and 2002. Neither of these used raw water cooling.

As virtually all Ownerships boats were "of a type", those of that type were similar.

In 1997 the boats were either the last of the Pat Buckle type or the first of the Graham Reeves (fitted out by John Milburn) type. To the best of my knowledge no Ownerships boat ever used raw water cooling.

However it is unlikely that the engine in Sunseeker is the original, most  BMC 1.8's lasted 8-12 years in shared ownership usage. That header tank is not typical of a BMC 1.8 installation if it is in a Graham Reeves shell fitted out by John Milburn. On the semi-trads they had a long pipe rising from the skin tank which the water expanded up, with a vented screw on BSP type cap. It emerged through a hole in the hexagrip cover ofthe gas locker on the port side of the boat (behind the morse control).

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

×