What denotes the size of a cars header thank? How much water it holds etc?

I have limited space/places to put one in my fiesta so will make up my own custom shape one to fit somewhere nice and snug but is there a specific way of working out its capacity etc?

Fords wrc tanks were small and obviously worked fine,

Also does it need to be the highest point of the whole system or just above thermostat level roughly

Thanks
Marc

 

The header tanks primary role is to provide room for expansion. So as long as there is "some" water in it when cold, that should be all it needs. But it can be good to have an excess of water purely as it increases the volume of coolant to the entire system.

"Some" is only really required so you can actually see the actual cooling system isnt dry. And in some ways, the more air space, ie expansion room the better. But that's the main role of the bottle. Too little and it can get blown out.

Too much....cant cause any problems.

 

a litre seems a nice round number
i'd go for that, with a good blow open cap incase theres alot of pressure

 

And ideally yes it should be the highest point in the cooling system. this enables any air to accumulate in the tank, and not form airlocks elsewhere. Also why any air bleeds always route to the tank.

 

Thanks guys,

Will make it roughly a litre then, and will use a standard ford cap

 

Hey Marc, if you give Andy G a ring he'll tell you what dimensions the he made for mine was. It's a decent Group A lookalike and would look ideal and save space in yours

 

Dont use the standard cap mate, make it for a bayonet cap, then you can up the pressure slighty for better cooling, and yes the vessel is for expansion for than anything

 

If youre paranoid about loosing water you can always fit a sensor to the tank so it lights up a warning light on dash so you know when the coolant loss reaches bottomish of tank.

 

I once remember an event did, sat on the start line, water temps all good, sat at 90deg, helmet on, you can't hear the engine too much only the co-driver, so, on the stage, doing really well, car starts losing power, hmm strange, looks at temp guage and for some reason, its gone back to zero, hmmmmm maybe the sender has broken, maybe the wiring has broken, thinking all this flat out (well was flat out till losing power) down shift, even less power, oil temp ok, water temp at zero.

eventually pulled over, and car had overheated (you can't tell engine temp in a rally car as it's fecking hot and fast as it is), only after a few mins of engine off did i realise that the water temp guage was not at zero, well it was, but it had gone all the way round back to zero off the top of the guage

Hence i alway use level sensors too

 

Found a guy breaking a group a car so have bought his header tank, has the valve fitted and a proper bayonet cap so I can pressurise it a bit to up the boiling point a bit,

Only Ł65 so not too bad, will add a coolant level sensor to be safe

 

Nice one Marc, that's what mine was designed off. Works and looks a treat