Any reason not to install a header tank?

Rivers & creeks

Rivers & creeks

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I have a Thornycoft 245 with a Bowman heat exchanger. The fresh water filling cap has a 2 inch copper overflow pipe which just vents into the bilge. When I do the weekly check on the coolant level I have no real idea if I'm loosing coolant and I'd want to know that ASAP! All I do is just top up but i dont know whether all i'm doing is overfilling each time, clearly on such a big unit there will be a largish amount of expansion. So I thought I'd add a simple expansion tank to the overflow pipe, is there any reason not to do this? Would it add pressure to the system? Does the expansion tank have to be above, level or below the heat exchanger?

Thanks for your advice.
 
The Lazy Kipper said:
I have a Thornycoft 245 with a Bowman heat exchanger. The fresh water filling cap has a 2 inch copper overflow pipe which just vents into the bilge. When I do the weekly check on the coolant level I have no real idea if I'm loosing coolant and I'd want to know that ASAP! All I do is just top up but i dont know whether all i'm doing is overfilling each time, clearly on such a big unit there will be a largish amount of expansion. So I thought I'd add a simple expansion tank to the overflow pipe, is there any reason not to do this? Would it add pressure to the system? Does the expansion tank have to be above, level or below the heat exchanger?

Thanks for your advice.
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engine coolant will normally get to a natural level, too much & it will spit it out via the l filler cap / over flow pipe.
if you fit an expansion tank you will have to remove the existing cap & replace with one without the spring, my tank is above the engine height
 
If its worked up until now without an expansion tank then it should be ok
Try a hose from the copper pipe into a plastic bottle to monitor overflow
Most engines will have a level that they will run happily and if you do overfill then they just push it out so next time dont refill but see what happens.
 
No need to replace the cap as I was going to take it from the overflow pipe. I think one of the attractions of a tank is I can put it in an easy to see place, currently checking the water level means climbing into the engine room. A tank would give an easy visual check when opening to engine room door to change the batteries to engine start.
 
The Lazy Kipper said:
No need to replace the cap as I was going to take it from the overflow pipe. I think one of the attractions of a tank is I can put it in an easy to see place, currently checking the water level means climbing into the engine room. A tank would give an easy visual check when opening to engine room door to change the batteries to engine start.
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with a header tank the sprung loaded pressure cap goes on that not the engine h/e;)
 
The normal purpose of an expansion tank is not only to take excess coolant expelled on expansion but to replace that water in the cooling system when the engine cools down and is normally mounted higher than the engine. Therefore connecting to the overflow pipe without changing the pressure cap will only allow expansion and not contraction on cooling as the valve on the pressure cap closes. All you would be doing is monitor the expelled coolant as Scottie suggests. That tank can be anywhere.
 
theoldsalt said:
The normal purpose of an expansion tank is not only to take excess coolant expelled on expansion but to replace that water in the cooling system when the engine cools down and is normally mounted higher than the engine. Therefore connecting to the overflow pipe without changing the pressure cap will only allow expansion and not contraction on cooling as the valve on the pressure cap closes. All you would be doing is monitor the expelled coolant as Scottie suggests. That tank can be anywhere.
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OK, that explains things. So I just need to put a pipe on the outlet into any old bottle, I know then if I've topped the level up too much and can work out the cold engine level of coolant to go for.
 
When I first had an engine with a heat exchanger I made the same mistake of filling to the brim only to find water in the bilge and the heat exchanger only half full. I soon realised what was happening. My engine runs happily with the coolant (when cold) just above the tubes in the heat exchanger. Any more coolant added just gets expelled when the engine heats up. I don't have a header tank. I did consider one but was advised it was not needed
 
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theoldsalt said:
When I first had an engine with a heat exchanger I made the same mistake of filling to the brim only to find water in the bilge and the heat exchanger only half full. I soon realised what was happening. My engine runs happily with the coolant (when cold) just above the tubes in the heat exchanger. Any more coolant added just gets expelled when the engine heats up. I don't have a header tank. I did consider one but was advised it was not needed
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Thanks, that's exactly what I've been doing and after a long run and cold, the level is only just above the tubes. I had begun to worry I was loosing coolant water, especially as there's an oil film in the water (no other symptoms of anything nasty happening).
 
Think you are confusing a header tank with an expansion tank. You should not need either. The coolant in the heat exchanger should be just above the tubes - there is usually some form of marker or an instruction to fill to so far below the filler cap. The gap allows for the small expansion when it gets hot. If the water level is falling you have a leak, if it is going out of the overflow pipe that means the pressure is too high for the cap - indicating either wrong cap or the coolant being overpresurised.
 
It seems I've definately been overfilling it, it was just above the tubes and I panicked and filled it up almost to the top, checked again and of course some had been expelled but not thinking right I just kept topping it up after each time we used the engine. The column to the pressure cap is about 3 inches high so all of that gets expelled if you fill right up.
 
As a maker of engines I can tell you "it depends".

IF your heat exchanger has spare capacity for expansion then you dont need another expansion tank - think 1960's cars.

If your heat exchanger is low volume then you do - like 1970's cars.

I suspect your heat exchanger is designed so that when the coolant is cold there is enough to cover the tubes and provide a path for circulation so you don't need an additional tank.

Expansion tanks come in two types, pressurised and not pressurised.

If you have a pressurised type the spring loaded cap goes on the tank, the tank is just an extension of the heat exchanger.

if its a non pressurised type the spring loaded cap goes on the engine - in this case the the cap and cap holder on the engine is designed to allow coolant back into the engine from the expansion tank as it cools. Normally as the engine cools air would be allowed back to prevent a vacuum, with an expansion tank we want coolant in the engine and air in the tank so the caps are slightly different.
 
I fitted an expansion tank, one from the breakers from a Corsa engine. Funny angled fixings but it's globular and fits in quite nicely. The big advantage is it is transparent (once I cleared out all the gunge!) so you can see your coolant level easily. If you have added antifreeze, I don't think it is a good idea to keep pumping it into the bilge.
 
Absolutely nothing wrong in fitting an expansion tank. I did this 16 years ago and it saves your bilge and engine drip tray. It does teach you to find the right level when filling your header tank. Any more goes straight to the expansion tank, once it heats and 'expands'. Doesn't need to be very big but helps if it is translucent and easily visable.
 
Thanks for those replies. It did strike me as odd that if expanded water could leave then air must get back, so I'll have a look at the cap and see what type it is.
 
If you think you are losing coolant other than by overfilling, just monitor the level.
If it nevers drops below a certain level ( the top of the tubes in my Bowman for example) , or you always needed to top up using the same amount of coolant then there is nothing to worry about.
 
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