>dollars.  I made a successful temporary fix with silicon sealant and a hose
>clamp to hold the plug tightly in place while waiting for the replacement
>part to arrive.
>>
>>I would not try a sealer for this one.  It the plug is cracked, the coolant
>system pressure could blow it sometime down the line.  I'm not certain
>turning off the heater will help either...I think the on/off valve is
>"after" the vent plug in the system in which case you still get the pressure
>on the plug.
Regardless of where the valve is, the core is still under some pressure
right? The valve merely prevents coolant from flowing through the core. If
you pull the core and take it to a decent radiator shop they will pressure
test it for you while you wait. If the core is leaking, they will probably
tell you that it can't be repaired because it is constructed from aluminum
and plastic, not copper. If you get a used core from a junkyard, be sure to
take it to the radiator shop for testing before you install it. Save
yourself some time and trouble. The local VW wrecking yard here (that has a
lot of VW stuff) said they had no aux heater cores that didn't leak. I just
spent a day trying to fix mine to no avail and then said screw it and
bought a new one from the dealer for $152. Remember, if this thing is
leaking you are compromising your cooling system for your precious engine.
Air will get into the system as the hot coolant cools down. Not good. Best
to get a good core, or take it out and plug the hoses. Hope it turns out to
just be a cracked bleeder plug.

-Mark McCulley