oil pressure differential .....
 

if you measure oil pressure coming out of the block .. and then when it returns to the block ..... Can that tell you if there is a restriction in the oil filter ..oil thermostat ...oil cooler ... loop ? I would guess there is going to be a drop but what is acceptable ?

Mike,
I did this test on my motor, put a gauge and shut off before my cooler.. if I can remember the numbers..
I cant pull them out of my head at the moment.. but I think I saw about 10 or so pounds of drop at 2500rpm and 20w 50 Valaline oil...
It will tell you if you have a restriction.. My main issue was what was the psi entering the block.. if that is good then a slight restirction isnt a problem.. I am running a Fram HP6 filter setup with #10 oil lines..
Hope this helps..
D*ck

Thats exactly where I am coming from .. I used the Russell AN fittings with pro clasic hose and one of the last fittings I put on the hose sliced into the inner part of the hose and created a flap in the path.... I redid that end but then got to thinking about the other 10-15 fittings that were already installed .... Also #10 lines ... I used the stock merc remote oil filter mount ( drilled out all the openings) ..then KE remote thermostats then thru 3x18" merc HP coolers ... I think a permanent Pressure gauge (mech) on the return to the block will be a wise move ....

I found I had two gauges.. that read the same and were low.. I ened up mounting my electric sender on the transom and then added a Auto Meter Mech gauge tee'd off from the electric sender... So Now I can bump the hatch and take a look to verify both gauges..

installed a mech gauge at the remote adapter (return) .... About 10lb pressure drop after the Filter/thermostat/cooler loop ...Gives me a good base .. just did the port motor but I guess I wont be happy til I add the other side too ......m

I hear u..
I ran across my notes yesterday on this subject. At the output of the motor I had 80psi at 1200rpm and 85psi at 2500rpm. Then I moved the gauge to the input of the motor and saw 70 and 75psi.. So it was a 10# drop across my cooler and HP6A filter, with the 20W-50 Valvoline. I cant remember how warm the oil was, but I believe I had been running the motor for a while so it wasnt stone cold...

D*ck

Mike,
Here is a pic of how I set up my rear oil psi gauge and sender for the dash mount electric gauge...