11.3 litres from totally empty, but you won't get anything like that in by just draining rad. Bit more if you drain block. Get five litres and mix it 50/50 with water. You will have some left for top ups. If you have blue in flush the system before adding red OAT.
Green or yellow is ethylene glycol, needs changing every 30,000 miles or so. OAT is reddish orange and lasts five years before it needs changing. OAT is recommended for the P38 M51 system.
