OK, You say it get's 'hot after 1 minute of running'. Does the fluid get 'foamy'? Making you think it gets hot, or is it too hot to touch?
What "type" of steering system do you have? I take it, that you have a 'pump, and rack' assembly. What is it out of?
Does it have a pump, control valve, and power cylinder? Early GM, and Ford passenger cars used this system. These systems are also easy to adapt into other older cars. Been there, and done that.
This could be as 'simple' as the P/S pump pulley spinning backwards, or a defective pump.