For a number of reasons, it is extremely important that the cooling system
can hold pressure.

Although the bulk temperature of the coolant may be less than 100`C, many
parts of the engine operate at temperatures well above that. Particularly
the heads and upper cylinder area. With the coolant not under pressure, it
will vaporize of these parts quickly making for poor heat transfer. The
localized flashing of the coolant will also cause pitting and corrosion of
these areas. If coolant is being added regularly, the air in the coolant
will further pit the cylinders. Ford Diesels had trouble with this due to
the diesel engine vibration. Many an engine would actually get holes in the
cylinders from this effect. Fords fix was to use a "water Wetter' additive.

Water also vaporizes at temperatures well below boiling. An non pressurized
system will require frequent topping off, More oxygen, corrosion, pitting)
and may cause the radiator to fill with air or steam.

The Bus Depot now has radiators available for a good price. I would
recommend replacing it now. It will not be much cheaper next year and will
probably be more expensive.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf
Of Lawrence Johnson
Sent: Sunday, October 14, 2001 10:00 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Coolant with Zero Pressure

The rad sprang a leak and to limp home I used a zero pressure cap on the
'pressure' tank. I used a spare old cap and cut the plastic valve out of it.
It
worked. Now I've plugged the rad leak enough that it won't leak at all with
the
zero pressure cap but I'm not sure if it will hold with the real pressure
cap.
What is the harm of running the coolant system with no pressure? I know that
the
coolant will boil at a lower temperature but that's not likely during a
Canadian
winter (is it?). I'd like to limp through until spring. Any
suggestions/advice
would be greatly appreciated.
-Larry
'86 Syncro Westfalia