Oil temp warning

I recently purchased a challenger RB46 round baler. This baler is made by agco. It is same unit as many of the older hesston/Massey balers. It has a self contained hydraulic system. Pto runs hydraulics and monitor controls all operations. No hydraulics from tractor. I keep getting oil temp warning on monitor after three or four bales. It seems that people have mentioned the oil resavoir is too small on this machine. Have any of you dealt with this? Suggestions? Thought about installing oil cooler on return line. Has anyone done this on a baler or have any ideas/pics of this?

Thanks

Oil temp warning