D6D caterpillar hydraulic system loss of oil pressure can u help?

Question

valves good, new lines, purged and cleaned system with new oil. temperature 190 deg drops 100 deg. after 30 minutes

Answer 1

Change filters. May have to loosen the feed line to the pump, may have an airlock. Install a flow meter in the system & check The GMP. If there is adequate flow then there maybe a relief valve sticking. There may be an electronic system hydraulic switch. You're looking for a 2" dia. round solenoid with two wires. Sometimes the shaft accumulates rust. You can remove the magnet & clean the shaft.
If all else fails there is always Finning. . .

Good Luck