1998 BMW 318ti radiator anti-amount

there is no "Set amount" usually a safe bet is either buy 1 jug of unmixed or 2 jugs of premixed if it doesn't fill it it will be safe to run on that untill you get more. rule of thumb is with vehicle off fill rad untill it stops taking it then burp the system be squeezing and releasing the bottom rad hose untill the level no longer goes down. then with your cap off start your car and slowly pour more in as needed untill it no longer takes any (yes it is safe to run with the cap off not safe to pop the cap after system has pressurized and engine is warm) this will allow for the system to evacuate any air and prevent air locks. while doing this make sure that you monitor the engine temp so that it doesnt overheat and make sure that you are getting heat inside the car. i recommend a thermostat change when changing fluid :) hope this helps