588's oil cooler question
 

Have an issue with high oil temp. co-related with high rpm hard driving. Other motor is A-OK . This has been a concern since coolers were new. can a cooler be defective itself ?
Is there something we may have overlooked ?
The only thing left besides the new cooler , which I need for my boat too , is to switch hoses from the thru hull fittings over. I tightened the packing nut and eliminated any excess fittings. Dropped the tranny cooler as well and noticed dirty blackened water . Backflushed everything. Re-sealed and tightened every fitting on sea strainer. Checked and re-checked all pluming hose routing, oil cross-flow and made sure everything is just so. I am leading to this being a cooler problem. It's real hard to swap coolers on this boat, so that's out.
Thanks for any input in advanve, BBB

The cooler is a $500 Hardin marine unit with a thermostat. Changed t-stats and also ran without. SSDD.
Water pumps are same , Jabsco Bronze , new Impellors. BBB