If you look at the radiator cap carefully (assuming you have the
correct one), you will find that it has THREE rubber sealing surfaces:
a big spring-loaded pressure valve, a small one-way relief valve,
and where it seals to the lip of the radiator filler neck.
As the coolant cools, the suction sucks the fluid back
from the overflow bottle into the radiator through the relief valve.
But beware that any leak in the system can keep this from working,
and it can end up leaving the coolant in the bottle and simply sucking
air into the radiator.
Check:
1: All three rubber sealing surfaces of the cap.
2: The mating surface of the radiator opening.
3: The plastic hose to the bottle should not be cracked,
and should fit properly on the little tube on the radiator.
3: The hose must be long enough to reach to the bottom of the bottle!
I have always needed to replace the plastic hose every couple of
years, because it gets discolored and shrinks. I use the clear
vinyl hose, which costs maybe 50 cents for the amount you need.
Rubber hose would last longer, but then you could not see inside it.
When the engine has cooled off, the plastic hose should be
full of green antifreeze, not air. If it is dry, you have a leak somewhere.
Doug Braun
'72 Spit
At 10:06 AM 10/19/01 , David Armitage wrote:
>Hi all,
>
>I've a quick question about the cooling system on my MkII Spit (although I
>think it pretty similar on all our cars). The expansion tank is there to
>accomodate excess coolant when the car is warm. Once the operating pressure is
>reached then the radiator cap allows coolant and hence excess pressure to be
>routed to the expansion tank. My question is what happens when the coolant
>cools and contracts? The radiator cap must surely be closed isolating the
>expansion tank from the rest of the system. I can't quite get my head around
>how the excess coolant dissipated when hot can get back to refill the system
>when cold.
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