One for all you physicists out there...

How much pressure is present in the cooling system when, say, 50/50 mix of tapwater/antifreeze is at 100deg C.? Is it significantly less than 0.9bar (13psi)?

I ask this, because I've just plonked my OEM 0.9bar rad cap in some boiling water (but with no antifreeze added), and the cap's spring didn't contract - i.e. open - at all!

 

The reason nothing happened is that your rad cap works off of pressure, not temperature. I.E if it's rated to 0.9 bar then the spring fitted will release at that pressure & keep the cooling system at 0.9.

Phil

 

As above, It needs to be tested with a coolant pressure tester. Hot water wont do a thing to the cap except make it hot

 

Great thanks - understand that.

So regardless of the coolant's temperature, it could be - within reason - at any pressure? And if that pressure happened to be more than 0.9bar then - because the spring's resistance to compression is rated at 0.9bar of pressure - this greater pressure acts on the underside of the cap, forcing it up by compressing the spring, which then allows the over-expanded coolant out via the expansion tank's overflow hole, yes?

 

yep. i see you have also asked about head gasget pressures. what is the exact problem? it is possible for the cap release valve to go faulty and release to early but it unusual

 

Yup dead right.

The excess coolant then gets transferred to the overflow tank by the battery.

If the over flow tank is overfilled then the coolant is then dumped via a tube onto the floor.

As the engine cools off, this creates a vacuum and the pressure cap allows the fluid to be drawn back into the system.

Phil

 

Yep, understand about that bit too ... Hence the theoretical phrase "lossless system", right

Cheers turbotits (love that handle lol), also . Good stuff, you two.