expansion tank cap - Pressure

[Steve Kramer]

All this talk about the coolant system is really timely with my v8.
Replacing the expansion tank helped.   I have also replaced the upper
radiator hoses. I also bled the system yesterday after I got some errant
temp warnings - even though the temp was at the 100 hash mark.  Now I hear
about the cap.  I bought one becuase I was hearing some hissing coming from
the cap.

Everything is doing fine.    My question is this - I'm not a gearhead - why
do you need the coolant under pressure ?  The system is moving the fluid
through the radiator via the pump.  Does the pressure keep the coolant temp
down ?

Steve Kramer
1990 V8q

----- Original Message -----
From: "Fisher, Scott" <Scott_Fisher at intuit.com>
To: <brett at cloud9.net>; <quattro at audifans.com>
Sent: Friday, May 24, 2002 10:00 AM
Subject: re: expansion tank cap


> Phil Payne once told the list that the caps were designed by Audi to be
> replaced after any loss of pressure.  (Odd -- I can't find it in the
> archives.  Found one of MY old postings about the first time I went
through
> the CGT's cooling system right after I bought it...)
>
> That's been my experience -- when I (well, the '83 CGT) lost a heater hose
> two years ago and blew coolant all over the engine bay, the car didn't
> pressurize properly even after replacing all the hoses.  I was afraid of a
> head gasket leak, of course, but I replaced the cap and it's been fine
ever
> since.  Because "ever since" includes several runs from roughly sea level
to
> 3900 feet at 75-80 mph in 100-degree weather with the air conditioning on,
> I'd support Phil's answer as being correct.
>
> --Scott Fisher
>   Tualatin, Oregon
>
>