We aren't talking about the cap leaking around the threads where air can
come back in. The normal leaking mode is that the pressure regulation
system of the cap fails and then coolant is easily pushed into the
overflow through the hose barb of the cap. Air can't come back the other
way unless the overflow tank is empty, since the cap hose discharges
into the bottom of the overflow tank, below liquid level.

Mark

Dave Mcneely wrote:
> Tom, if the pressure cap is leaking, then air can enter it just as coolant can escape.   mcneely
>
> ---- Tom Carchrae <tom@CARCHRAE.NET> wrote:
>> This is not a different issue - this is my cooling issue....  :)
>>
>> I have a question to ask the experts regarding the bad cap theory.  I get
>> how the fluid ends up in the overflow tank - but if it just a cap, where
>> does the air/gas come from the displaces the coolant - and why does it not
>> pull the coolant back into the pressure tank when it cools?
>>
>