Yes mine has a fairly new cap on it & it is a 7lb one.
Usually a recovery cap has a rubber seal down in the bottom of the neck as well as on the very top. The one I have has the seal down but not on top. Just a brass to metal seal. As my recovery bottle is well down in the bilge
I suspect it's sucking air long before it recovers coolant
. I'll try raising the overflow bottle & if that doesn't work I'll look for a proper recovery cap.
The 'official' 4-108 manual specifies the coolant
level to be 1" below the neck so keeping the header tank full doesn't appear to be essential.
No one game
to comment on the thread size & pitch
for the engine
drain tap on the side of the block under the exhaust