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.

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.

You could do but need to allow for expansion somehow.

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

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

quote:

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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

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quote:

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Originally posted by SteveWalker

quote:

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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

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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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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

Thats great, thanks for that info, i can crack on with it now with a bit of confidence