Combines F Head IJIJ

Sounds like a worn hydraulic pump. When the oil gets hot it has too much wear between the gears and pump body to build enough volume and pressure. There is a repair kit available to replace the gaskets and wear plates that you can try. However, if there is much wear in the pump body it will take a new pump. I won't tell you what a new one cost me 20 years ago as it would just be too depressing. Also, if it does not have the hyh. oil cooler option installed putting one on would help.

The first thing to check is the filter in the hydraulic system. Make sure he is using fluid (Dextron_Mercon) in the resevoir. The next thing to check is the filter. There is a filter in the system by the resevoir and valve stack. Take it out clean it and try again. Next thing to do is change the fluid (when it's brown it's broke down) so that it is nice and red. The next thing to do is to make sure the valves in the stack aren't sticking because when they heat up enough and expand that could become a problem. The last thing to do is to check the pressure of the lines and the last thing to do is to rebuild_buy a new pump. You can go with a bigger one, we did on one machine. It is a common pump and cheaper. let me know how you and your friend make out with it, they are good machines.