has the standard merc power steering cooler

ok, it has a lot more steering fluid. that is not an issue. BUT; is it under a heavier load to steer, and does it run under load all the time? or just when moving the steering wheel? i know the steering feels very light, but it could take a lot more pump pressure to turn, and it could keep the pump pressure high even when not turning the wheel. i don't know the answer, but it is what needs to be found out to find the solution to your problem. it could be a bad saginaw or brazil valve and the setup is fine. it could be nothing is actually wrong, it just generates too much heat for that cooler...

we are going to investigate the cooler its the standard merc 6" cooler which is on a lot of boats with no ill effects, however maybe it has a restriction or corrosion

ok, call AGR they build the pumps used in the marine industry, talked to them a while back on a problem, was told that the "marine" pumps used a bearing instead of a bushing because of the very issue you stated, so maybe sometime a reg car/truck pump was installed and this is the issue, now I have installed truck pumps before, switched out the pressure regulator and have had no issues, but I did buy one of their $$$$ pumps when I did my full Hyd system.

we switched out the cooler with one that I had on shelf ( only slightly used) and replaced the high pressure line
I know we should of only done one at a time but that would have added time to put in water and test each but Problem solved now no heat at all cool to ambient air temp after 5 min 4000 rpm run , before would have been smoking

thank you all for your comments and suggestions

cool beans. in this case, literally.

Glad you got it fixed.