Sometimes I miss the obvious. Used the Gates flow calculator and realised I had introduced an unnecessary pressure loss to my oil circuit.

Before I get ridiculed, here is context. I live 500km from the most remote city on earth. So quite often have to be resourceful with what's on hand or wait forever for part deliveries. During the build I had just grabbed some new hose & fittings from my farm workshop to hook up the oil cooler to the engine, had every intention at the time to replace with lightweight hose & fittings but over the build time just plain forgot. Thought I had the size right but didn't count on so much loss with such low oil operating pressures & flow. but still should've tagged those parts. So before I order a new cooler, I'll try it with larger hose.