Thoroughly confused myself as I thought the cooling system plumbing would be easy until I started reading a few threads on it. There is a difference I think between an expansion tank and a header tank or I am wrong ???
I am trying to plumb up a black top zetec using the standard ford thermo housing. The radiator I'm using has a standard rad cap with overflow pipe attached.

Do I need a header tank or expansion or does it not matter? Do I to make any changes to the radiator cap setup ? Do I let the radiator overflow pipe vent to atmosphere ??

Any help appreciated as I'm well confused now !!!!

unless someonecorrects me, expansion tank has a pressure cap and is sealed whereas a header tank is vented to air.

the header tank connects to a pipe in the radiator neck. as water expands, it pushes the cap open and flows into the header tank. when it cools, anotehr valve in the cap opens and water is drawn back in. the cap on the radiator controls the water pressure.

expansion tank has cap that vents both ways but itvents air - something is serioulsy wrong if the expansion tank overflows.

Nope, wrong way round - a header tank has a pressure cap, an expansion tank doesn't

You definitely need a header tank or your cooling system wont be pressurised and the coolant will boil at too low a temperature. It's not actually vital for the operation of the cooling system to have an expansion tank (as long as you make sure the header tank is always full) but it's an extremely good idea as it ensures the cooling system is always full for one thing and the other good thing is that it stops boiling coolant being sprayed around your engine bay if your engine gets too hot.



[Edited on 11/8/08 by D Beddows]

No clear definitions on this but generally you could say expansion bottles don't have flow through them but header tanks do. On european vehicles both are generally pressurised.

If you have a conventional old fashioned vertical flow rad (ie Cortina style) the header tank is generally the top of the radiator. With this type of system you can also add a non-presurised expansion bottle catching the overflow from the rad --- a lot of Japanese vehicles use this for example 1990's Hondas and Honda engined Rovers such as the 600.


One thing to avoid is having more than one pressure cap on the system as this can lead to airlocks forming when the system cools.

[Edited on 11/8/08 by britishtrident]

So does this mean I can replace the valved radiator cap with a valve less unit and block off the overflow and use a header tank with a pressuresied cap ????

Will the header tank cap release pressure if the system over pressures ??

With an old style vertical Cortina or similar with the pressure cap on the top of the rad don't over fill the radiator it needs an air space at the top to accomodate expansion --- old style rads with the pressure cap at the top should only be filled to within an 1" of the top or roughly 1" above the radiator core when cold.

[Edited on 11/8/08 by britishtrident]

quote:

---

Originally posted by Cubby
So does this mean I can replace the valved radiator cap with a valve less unit and block off the overflow and use a header tank with a pressuresied cap ????

Will the header tank cap release pressure if the system over pressures ??

---

i am using a zetec blacktop and have no rad cap on the rad and a pressurised cap on the header tank. small bleed hose on the rad has also been blocked and the small hose on the thermostat housing is plumbed to the top of the header tank