Doesn't matter garden hose or lake. As I put my hand on all the primaries coming from the block the only hot one was port side closest to front of engine

Check oil cooler water side for blockage.

Correct.

This is what I found in mine. The boat didn't have strainers.

Wow that is a ton of debris. What side is the water side? And does it come apart like the heat exchanger does on each end?

Seawater flows thru the cooler. Inside is a honey comb looking series of tubes. Oil flows around these tubes cooled by the water flowing thru on the outside. These small hole opening tubes can become blocked/clogged by debris and become a restriction. No endcaps. Loosen breeze band clamps and remove rubber water hose to access seawater side.

This is due to the routing of the water from the big heat exchanger. When you take the endcaps off, looking at the water flow path, Water from the sea pump comes in the port side, flows across the HX makes a turn and goes back across, before it makes the turn, water flows to the starboard header. So your starboard header gets more cool water than the port side. I am still trying to figure out ho to balance the temps out myself. Most would probably say not to worry about it, but I just don't like it.

Good beer there ^^^ .