This may be a non issue but I am curious having read many posts on the topic of oil pressure, and filter type.

I haven't seen a schematic, looked and cant find one. (Does one exist?)
Have seen a couple videos, but they dont show enough to tell me much.
Also, haven't ripped apart the filter housing/adapter to find out. how the oil flows from the pump

I'm guessing somebody here knows the answer:

Does the pressure sending unit measure the pressure before or after the filter?

Part of me would think it would be downstream of the filter so if you filter got clogged the gauge would read low indicating you have a problem.
Or the gauge could be upstream of the filter and rising pressure would indicate a clogged filter.

Hmmm

 

After the filter.

 

Thanks, got some stuff to attach a gauge to the sensor port (still need a tee) to verify oil pressure on a 2001 XJ that just got a new head (had a cracked 331).

Pressure is low when hot at idle, i fear bad bearings and more work coming.