Mercury wtaer pressure dump valve issue
 

So I installed a Merc water pressure dump valve on our mildly built 502 MPI engine this summer to back the water pressure down some and while it is working, it pulsates while running which in turn causes the gauge to bounce around.
Anyone else have this issue? if so, how did you correct it so it dumps steady and constant?
Dump valve is in hose after oil cooler and before circ pump per the directions. Oil press gauge hose is in side of block on starboard side.
Any help would be greatly appreciated as it drives me nuts watching it pulsate!

My spelling sucks today! meant to say water pressure dump issue and the hose for water pressure is in side of block.