Re: Checking lower units with air pressure Home › Forum › Ask A Member › Checking lower units with air pressure › Re: Checking lower units with air pressure chris-pReplies: 2456Topics: 153 August 12, 2018 at 8:56 pm #81027 I use 5 psi. I sometimes also check double lip seals at 10psi. Be aware, too much pressure can actually cheat a test, depending on lip orientation.