merc 260 manifold/riser - no water flow to upper water exit port on risers

Hi guys- i have a 4 hose raw cooled system.. one hose to underneath manifolds and one to risers, with the check ball setup- I have a new water pump installed,tried restricted gaskets (which i believe are correct?) and regular 4 hole open riser gaskets - same symptoms both sides.. the lower half is lukewarm after 1 minute runtime, upper half is scalding hot - i cleaned the risers and manifolds out real well, they dont even look awful at all - and the ports are open, no water is making it up there though-

T-stat housing:



I am considering blocking off the fwd riser slot/port completely so that the raw cold water entering the front of the riser can be forced upwards and out the top of the riser exit, and the warmer water entering below the manifold can use the remaining 3 slots to exit the riser on the lower side-

thoughts?

Is it possible the alpha pumps dont have enough volume for the later bravo/center style manis? Also - which of the 3 tstat gaskets should i use? my tstat seems blocked there anyway where the small hole is, just looks like a dead hole - is that wrong?

you use the 3rd gasket to the right

thanks - so i guess my housing must be bad/blocked because theres nothing open behind there.. blocked. Ill try drill it out and see- probably replce it otherwise.. thanks