I seen this problem with bendi and found steer control valve faulty. you can diagnose in steps as below.

let start from control valve and pump itself. remove all connections from control valve including steer connections. run the hydraulic motor, oil will go back to the tank via control valve return system. run fro a while and not the temperature.

on the next step connect the steering hoses only, run for a while and note the temperature.

remove steer and connect the tilt system. run for a while and note the change in temperature.

now connect the lifting hoses and check it as well.

it is bit lengthy but you would be able to find out what exactly the problem is. You may do it once battery in the forklift and once putting battery out side.

keep posted the TS details.

Regards,

Addy