Yes, the coolant level in the refill tank will go up when hot and down
when cold due to the expansion of the coolant, so your cap is fine.
That is why it is usually called a "coolant recovery tank".  In the old
days excess coolant used to dump out on the ground, and then there was
an air space at the top of the radiator for this expansion.  Not allowed
anymore, the systems today are closed and have no internal air, as
anyone who has bled a Vanagon cooling system knows!

If your tank is emptying repeatedly and you have to add coolant, you
have a leak somewhere.  Check the rear heater core first, it is quite
often the culprit and the easiest to fix.

Stebbins wrote:
>
> I suspect that my coolant reservoir cap is bad as my
> overflow tank (Bentley calls it a "refill tank" pg. 19.13)
> is always dry, even when the engine is warm/hot.  Do you
> guys actually SEE the level of coolant going up and down in
> the overflow (secondary) tank as the engine heats up??
> Thanks,  Malcolm

--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)

Assisting on Restoration (and spending OPM):
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT