Hey everybody first time on Mack forum, I'm working for a farmer and hes got a couple old Mack's that I'm working on and I cant get any info about these old trucks and I was wondering if maybe someone on here could help me out? I dont even know where the block drain is on this truck or the proper way to even flush it to be honest. I found a drain on the bottom elbow of the main big pipe coming out the bottom of the rad and beside that is a little brass valve; does that valve have anything to do with draining the block? Or do I just drain that plug and it's that easy? The truck is a 1975 Mack RL600L. Any help will do thanks!