Originally Posted by Labnerd

The Mercon fluid used in your transmission is tested at 302F for 83 hours. The test has 20,000 clutch cycles at 88 joules per CM2. In most cases, ATF mirrors coolant temps. Your old tranny at 160F was too cold and I'm surprised you didn't have seal issues. Ideally you want the ATF to run between 180f and 200F. It's when temps get over 230F you need to back off and let it cool down. There is no need to change it. ATF is more like hydraulic fluid in that it doesn't see combustion gases or acids. It can last a long time.