engine knocks when cold
 

my 92 500sel knocks when cold in morning start. it knocks for 15 seconds until oil pressure come up to 3 and knocking ends. I changed oil with
(0w40 mobil1) filter and oil pressure sender. I heard there is a valve in oil system that keeps oil in system once car shut. Any info about that valve or any ideas how to stop knock is apreaciated
Thank you
Victor

is the sound
 

a knock (deep) or a tap (higher pitch)?

if it is more of a tap it may just be the valve adjuster, which is not to worry about and often can be solved by a change in oil type.

a knock can be serious.

main bearing noise is not a good thing.

tom w