It is my belief that normally the threads do not provide the seal.  Rather,
the very edge of the tank neck seals against the inner layer of the cap
which is part of the valve assembly.  That said, the tape on the threads
could provide an alternate seal.

After many experiences with bad caps, including new ones, I continue to
look for a solution.  I hope to retain a tank that is transparent to let me
watch for accumulating air.  In a junk yard somewhere, I hope to find a
radiator neck long enough and of a reasonable diameter that uses a "real"
metal cap.  If this neck could then be somehow glued into a wbx tank, maybe
I would be satisfied.

Larry A.

On Thu, Oct 29, 2015 at 8:29 AM, Stephen Engel <sengel543@yahoo.com> wrote:

> Get some plumber's Teflon tape and wrap around the threads on the tank a
> couple times. It stopped my leak until the new cap came. I still use it
> with the new cap, the threads on the tank are still old. It's available at
> hardware and home improvement stores.
>
> Steve
> 87 Syncro
>
> Sent from my iPhone
>
> > On Oct 28, 2015, at 4:01 PM, Stan Shapiro <mail@STANSHAPIRO.COM> wrote:
> >
> >
> >
> > My blue coolant cap is leaking slightly. I have another cap on order it
> will take 2 days. Any suggestions on what I could do that temporize the
> leak while I'm waiting for the cap?
> > Here's the sad part, after reading this board, about a month ago I
> ordered two new caps but they were delivered to my house a few days after I
> left on this trip.
> > Stan
> >
> >
> > Sent from my Verizon Wireless 4G LTE smartphone
>