Expansion vessels in on skin tanks

[Paul Conroy]

Hi. My current narrow boat engine cooling arrangement comprises of two skin tanks on opposite sides of the engine bay. They are typical vertically mounted tanks, of about 5 sq.ft surface area each. They work fine with my current engine, a Perkins P3.152 (if anything a bit too well as the temp gauge rarely gets above about 70 degrees). However,  one of the tanks has a small expansion vessel fitted to the top corner, nearest the bulkhead and it has an overflow pipe by the vessel filler cap, leading back down to the bilge. 

My basic question is whether or not this is a good system? It seems so to me as it would presumably vent any air. However, I am fitting a new engine due to issues with the old and I am concerned the vessel is a bit small and may overflow if the new engine runs hotter and with a more powerful pump. I guess it is a case of trying it out and changing things if necessary, but would appreciate advice from others.

 

Thanks, Paul

 

 

[PD1964]

What engine are you fitting and is it brand new?

 Is that expansion tank inlet(copper pipe) connected to the engine cooling pipe work or connected direct into the skin tank?

  

 

Edited September 8, 2021 by PD1964

[Tony Brooks]

Personally, I would prefer a larger one and would not like plastic pipe just hose clipped to plain metal pipe. Too likely to blow off when the system is under pressure. This may be why you seem to have no pressure cap and why it seems to have a 72C thermostat fitted. A newer engine is likely t be expected to run pressurised. If your present engine does not have a pressure cap on it, then what you have is simply an air vent, so volume is not important (assuming the tank is higher than the engine filler point). Assuming this is not a direct raw water cooled engine coupled to a skin tank.

[Steve56]

You need to calculate the total water capacity of your cooling system and then look at the expansion rates of the coolant. This will then give you the size of header tank required

[Paul Conroy]

Thanks for this advice. Just for clarification, the new engine will be a Beta 38 and this little tank connects directly to the top of the skin tank. It is keel cooled.

Regards, Paul

 

 

 

[Jen-in-Wellies]

9 minutes ago, Tony Brooks said:

Personally, I would prefer a larger one and would not like plastic pipe just hose clipped to plain metal pipe.

It is leaking already, judging by the green corrosion on the copper. That type of fabric reinforced PVC hose tends to go hard over time and leak. A better way of doing this would be with car heater hose and put a compression fitting on to the copper pipe that ends in a fur tree fitting for the heater hose to push on to, with a hose clip over the top. A cheap way of doing it is to have a copper pipe with a compression olive compressed on the end, which again helps prevent a rubber pipe blowing off when used with a jubilee clip.

[Tony Brooks]

1 minute ago, Jen-in-Wellies said:

It is leaking already, judging by the green corrosion on the copper. That type of fabric reinforced PVC hose tends to go hard over time and leak. A better way of doing this would be with car heater hose and put a compression fitting on to the copper pipe that ends in a fur tree fitting for the heater hose to push on to, with a hose clip over the top. A cheap way of doing it is to have a copper pipe with a compression olive compressed on the end, which again helps prevent a rubber pipe blowing off when used with a jubilee clip.

 

Not only does it go hard, but when warm/hot is also creeps away from under the hose clip so it is no longer gripped tight.

[Jen-in-Wellies]

29 minutes ago, Paul Conroy said:

Thanks for this advice. Just for clarification, the new engine will be a Beta 38 and this little tank connects directly to the top of the skin tank. It is keel cooled.

Regards, Paul

It sounds like this plastic vessel is used as a combined bleed point to remove air from the skin tank and an expansion tank.

You said in your first post that the engine rarely gets above 70C. If there is sufficient skin tank size, then the engine temperature is determined by the engine thermostat. Is there actually a thermostat fitted? What is its opening temperature? Within reason, you can't really have too much skin tank area. However more tank will increase the overall coolant volume, so will require a bigger expansion tank to cope with the water expansion as it warms up. My Beta 43 relies entirely on the air space above the coolant in the exhaust manifold cooler thing and doesn't have an external header tank at all. Never had a coolant loss problem with it, including tidal river Trent trips, so this works fine. Other Beta 43 installations do have an external expansion tank. The Beta 38 you are planning to install will also have some expansion capacity built in to the marinisation by Beta Marine. You'll need to do some sums on the total coolant volume and its expansion from say 10C to 100C  to see if this is sufficient. Water volume expands by 0.0002 times per degree, so 20 litres of water raised by 90C will take 0.36 litres more space. The coolant is an antifreeze/water mix, but it shouldn't be far off.

Jen

 

[Jen-in-Wellies]

More. Engineering Toolbox says water has a volumetric expansion coefficient of 0.000214 and ethylene glycol (a lot of antifreezes) is 0.00057, so a 30% glycol antifreeze mix will be around 0.00032/degC.

Jen

[Paul Conroy]

Jen, that is great information. Thankyou!

 

p.s. not sure what my thermostat operating temperature. I realise that I better check it - I was a bit oblivious to the fact that in a properly cooled system, it is the thermostat that controls the running temp!

[Tony Brooks]

With that tank connected as you describe, it is impossible to say if it is an expansion tank or not. To be clear about that, we need its relative height to the engine filler and to know if the engine filler has a well seated pressure cap on it or not.

 

The Beta will have a pressure cap so you will need one with a good seal on that tank and the one on the engine will need attention to ensure it does not vent before the one on the expansion tank. Incidently the tank one seem to be leaking now I have enhanced your photo. You can see the rust stains around the neck. If there is no overflow on the Beta filler neck you could put a plain rubber sealed cap on the engine and, as long as the neck lengths are similar, the Beta pressure cap on the expansion vessel. I suspect the expansion vessel neck will be longer though.

[Bee]

Every chance that the new engine will have a pressure cap and small hose to cope with expansion but an expansion tank on the keel cooler tank won't hurt and could help with air venting. Can vouch for the hopeless practice of shoving a copper pipe into a hose.  Happily cruising along some years back when there was a 'pop' and the galley was full of steam and hot water. The rubbish boatbuilder (might have been me) had done just that under the sink.

[TheBiscuits]

12 minutes ago, Bee said:

Can vouch for the hopeless practice of shoving a copper pipe into a hose.  Happily cruising along some years back when there was a 'pop' and the galley was full of steam and hot water.

 

If you have to do it, stick a compression fitting on the hose end of the pipe, tighten it thoroughly then remove the fitting leaving the olive in place.

 

The hose then pushes over the olive and gets jubilee clipped in place.  The ridge made by the olive prevents the hose coming off.

[Tony Brooks]

54 minutes ago, TheBiscuits said:

 

If you have to do it, stick a compression fitting on the hose end of the pipe, tighten it thoroughly then remove the fitting leaving the olive in place.

 

The hose then pushes over the olive and gets jubilee clipped in place.  The ridge made by the olive prevents the hose coming off.

 

Better still, use a proper hose tail with multiple ridges.

[PD1964]

I would get rid of that tank, speak to whoever is fitting your engine, it looks like it’s attached to the skin tank filler, so just cap it off.

  I’m sure a Beta 38 can run without an expansion tank if the heat exchanger coolant fill cap on the engine is the highest point in the system, however if you have coolant pipes running to a Calorifier or other heating system which is higher then the exchanger/cap you’ll need an expansion tank at the highest point. Beta Marine do an expansion kit if needed so just buy that, one may come with the engine. 
 The engine fitter should know all this and get the engine and cooling system installed correctly, if he is a Marine engine fitter???
 

Edited September 9, 2021 by PD1964

[Paul Conroy]

Thanks all for this good advice. To answer one or two points: 

1. The tank in my photos is the highest point in the engine coolant system, though the top cap is only about 10cm above the engine coolant filler cap

2. The engine filler has a proper radiator cap, but I do need to look a bit closer to check it seats properly and is operating as such

3. I did ask Beta about fitting one of their expansion tanks before I thought about doing anything to this skin tank expansion vessel, as my calorifier pipework is about the same height at the high point as the Beta 38 engine filler will be. They thought it would probably be unecessary and I have venting points on this to release any tapped air

4. I am sure my marine engineer will also be able to advise, but I am keen to understand the issues and I may well do some of this plumbing myself

5. I am tempted now to remove the expansion tank and have a suitable air bleed valve fitted to the skin tank

 

Anyway, I have had lots of insightful comments and can now make an informed decision as to what to do.

 

Thankyou, Paul

 

[Tony Brooks]

Unless you were able to tell Beta the coolant capacity of your skin tank and pipes, I could not be confident with what Beta said. There have been reports of Betas (and other engines) air locking themselves because the coolant volume was so large when it cooled, it drew air into the engine that got trapped when the boater topped up the following morning, but as long as you are aware of the possible problems suck it and see. You can always retrofit an expansion tank if it turns out to be needed.

[PD1964]

1 hour ago, Paul Conroy said:

5. I am tempted now to remove the expansion tank and have a suitable air bleed valve fitted to the skin tank

 

Anyway, I have had lots of insightful comments and can now make an informed decision as to what to do.

 

Thankyou, Paul

 

Just cap it off, no point in having a air bleed valve there if lower then engine coolant filler or expansion tank. Only seen skin tanks with sealed cap offs.

[Tony Brooks]

Then you have not seen the one on JennyB (Rugby boat builders for Viking Afloat). A bit like the OPs but larger and made of steel. Open vented and the top just below the deck boards. Perfect for self bleeding the whole system.

[PD1964]

55 minutes ago, Tony Brooks said:

Then you have not seen the one on JennyB (Rugby boat builders for Viking Afloat). A bit like the OPs but larger and made of steel. Open vented and the top just below the deck boards. Perfect for self bleeding the whole system.

He says he is thinking of removing it and fitting an air bleed valve to the skin tank, which implies fitting to the top of the skin tank. What’s the point if it is lower then the new engines coolant filler or expansion tank? You quoted one boat, so obviously not the norm in Narrowboat shell building as all the skin tanks I’ve seen have had sealed blanking plugs on their skin tank fillers

Edited September 9, 2021 by PD1964

[Tony Brooks]

Thee is no reason he can't fit the bleed on the top of the pipe. There is no reason other than convention that means the bleed point has to be directly on the top or side of the tank. In many cases it would be far easier if the builder had thought enough to fit  a proper bleed point in the sink tank instead of a plug or cap. In my view, it is vital that skin tanks are fitted with a way of venting the air/gas that can get trapped in them. Without any tank bleeds you are expecting air to flow back into the engine against the Uttar flow or move downwards through the skin tank and into the return from the tank. That often  does not work.

[PD1964]

28 minutes ago, Tony Brooks said:

Thee is no reason he can't fit the bleed on the top of the pipe. There is no reason other than convention that means the bleed point has to be directly on the top or side of the tank. In many cases it would be far easier if the builder had thought enough to fit  a proper bleed point in the sink tank instead of a plug or cap. In my view, it is vital that skin tanks are fitted with a way of venting the air/gas that can get trapped in them. Without any tank bleeds you are expecting air to flow back into the engine against the Uttar flow or move downwards through the skin tank and into the return from the tank. That often  does not work.

Well obviously most shell builders and boat fitters in the country do not think the same way as you and just fit blanking plugs to their skin tanks. 
  I’m sure everything will be ok with the new engines air bleeding and cooling.

Edited September 9, 2021 by PD1964