EJ 22 Oil Pressure problem

Hi Guys
Engine is a 1994 EJ22
Had a problem with my thermostat and the engine got quite hot about 110 deg C at one point as i limped back home .
Have since added a oil pressure gauge and after fixing the thermostat .Oil pressure Ok on startup then fades away as it warms up.
The oil pressure is very low when engine has warmed up (5 mins ) and the oil pressure light also comes on
No engine noises and the oil presure light was working fine before the overheat
Will be changing the oil and filter tomorrow and checking the oil pressure relief valve
Any ideas on what to check after this
Cheers Gaz

How old is your oil, viscosity?

Found the problem today
The engine could not breathe once the dip stick was removed pressure returned
So all breathers from engine went into one 4 way connector which then went to the air filter pipe this was blocked
Well thats one down and a few more glitches to find
Cheers Gaz