andrew-theasby
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| posted on 15/10/09 at 08:55 PM |
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why do you need a header tank?
Can someone please explain to me why you need a header tank, i realise you need somewhere to bleed any air off but once its bled, could you have a
sealed system? Was just wondering if you could put a filling point in the top hose with a pressure cap on and a bleed nipple on, and do away with the
header tank? Thanks.
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MikeRJ
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| posted on 15/10/09 at 09:02 PM |
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All cooling system are sealed, irrespective of a header tank. A header tank has a constant circulation of coolant through it which helps to remove
any air from the coolant, and the header tank also provides the air space to allow the coolant to expand as it gets hot.
You can run a system without a header tank, but you will need some way of allowing the coolant to expand without losing it. A simple expansion tank
used in conjunction with a radiator cap that has an extra valve so the coolant can be drawn back in from the expansion bottle is one method.
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eznfrank
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| posted on 15/10/09 at 09:03 PM |
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You could do but need to allow for expansion somehow.
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minitici
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| posted on 15/10/09 at 09:08 PM |
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When I sprinted a Cox GTM, I twice had problems with a split header tank and temporarily by-passed the tank.
First time a convoluted hose blew going round Knockhill race circuit.
Second time the radiator core blew on the motorway whilst returning from the Kames Sprint circuit.
Water needs somewhere to expand 
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andrew-theasby
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| posted on 15/10/09 at 09:15 PM |
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Sorry, didnt exactly mean sealed.
So as the engine heats up, the water expands and the air effectively shrinks and pressurises, is that right? Where does the constant flow through it
come from? is that only from the small amount from the "bleeding pipes" how small can you go with the header tank then? or, more what im
asking is, how much air should be in it? Thanks
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SteveWalker
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| posted on 15/10/09 at 09:15 PM |
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quote:
Originally posted by minitici
When I sprinted a Cox GTM, I twice had problems with a split header tank and temporarily by-passed the tank.
First time a convoluted hose blew going round Knockhill race circuit.
Second time the radiator core blew on the motorway whilst returning from the Kames Sprint circuit.
Water needs somewhere to expand
What you should have done is bypass the header tank, but only part fill the system, allowing some room for expansion.
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minitici
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| posted on 16/10/09 at 08:58 AM |
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quote:
Originally posted by SteveWalker
quote:
Originally posted by minitici
When I sprinted a Cox GTM, I twice had problems with a split header tank and temporarily by-passed the tank.
First time a convoluted hose blew going round Knockhill race circuit.
Second time the radiator core blew on the motorway whilst returning from the Kames Sprint circuit.
Water needs somewhere to expand
What you should have done is bypass the header tank, but only part fill the system, allowing some room for expansion.
Or just not drive the car would have been better.....
The GTM had a front radiator/ rear engine configuration and it was all too easy to get an air lock in the pipework - partial filling would have just
made said airlock and again no cooling.
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Bluemoon
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| posted on 16/10/09 at 09:06 AM |
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To calculate the expansion volume needed (i.e. the minum amount of air in the header tank) do the following:
1) Water expands by 4% by volume from 20 to 100C. Calculate this volume.
2) If you want a pressure cap of 15psi you and you don't want it to vent you will need twice this volume.
i.e. for my 9ltr system I would need
9ltr*0.04*2 = 0.72ltr
i.e. 0.72 ltr of air space in the header tank with the engine cool.
But I would want a bit more in case you have a small amount of air in the system (i.e. when you first fill it) so say 1ltr of air space (or more) in
the header tank would do..
Hope that helps
Dan
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andrew-theasby
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| posted on 16/10/09 at 08:15 PM |
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Thats great, thanks for that info, i can crack on with it now with a bit of confidence
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