Cooling system query

[simon]

I'm a bit confused how an expansion tank works on a cooling system.
The cooling system in a car is a closed, pressurised system, If there is an expansion tank fitted, where is it fitted to?
I have an overflow on my filler cap neck, but that is on the outside of the pressurised system and any fluid seeping out there cannot be drawn back past the radiator cap.
Surely if I connect an expansion bottle to the small pipe on the header tank (currently connected to another small pipe on the rad) then the system will not pressurise properly?
I'm confused...
Simon

[kdavies3]

Hi Simon,
Your header tank if it's like most systems will be the highest point of the system. This should not be filled completely full (once the system is fully bled anyway) this will allow it act as an expansion tank when the system is hot and pressurised.
The small pipe at the top of the rad filler neck can only work both ways if you do not use a pressure cap, but a blanking cap (they may look the same externally).

hope this helps

[simon]

Thanks Kev,

Thats more or less what I thought.

Simon

[SimonP]

Your pressure cap then goes on the expansion tank of course!

Simon.

[osgood]

Simon, the expansion tank is genraly fitted below the level of the header tank & feeds into an inlet on the tank at the top, but not the one beneath the preasurised cap which is an overflow! When coificiant expantion takes place the water is dragged in; filling the tank or radiator. When in normal running moad the header tank ditches out what it does not require & suckes it back in again when at iddle when heat rises. Eric.

[Dutch Paul]

This is a prime example of us needing a spell check on this forum
How about it Robert?

Just a thought

Paul

[gartrac]

[center]
Kev

Sorry to correct you but a pressure cap can and does work both ways.

If you take a look at the underside of the cap there is a small disc valve held closed by a very light spring, as the system cools down air or water, if an expansion bottle is used, can be drawn back through the this valve to replenish the system

I think the term expansion tank is misleading as it is actually a header tank normally used to ensure the cooling system is always full reducing the risk of air locks

Pete

[kdavies3]

Pete, I disagree, I'm afraid.
The disc carrying the rubber washer (pressure cap), as you say is spring loaded.
This is variable depending on the application, but a common one is et to blow off any excess pressure in the system at 1.0 bar. Other than then the cap is sealed, otherwise air would potentially be drawn in to the sytem every time it cools down.

Kev Davies
Dax, 383ci Chevy Stroker, Tremec TKO
South Wales

[simon]

So, If I have a pressure cap on my header tank, and the pipe leading from the filler neck is just an overflow, and the other small pipe from the header tank goes down into an expansion bottle, does the expansion bottle need a pressure cap as well?.
If not, surely the system is not pressurised, but if so, how would the system draw water back without collapsing the expansion bottle?
Confused!!

[osgood]

Sorry Paul, must be the Whisky chap!!!!! (coefficient expansion)which is a multiplier, got that wrong way as well!! But I think I everone gets the drift.

Recon we could do with a dictionary as well Robert, for those of us that have not been honoured with Public School education. Eric