I don't think that the radiator has to be drained for efan install. I just threw the efans in with the staement because they will be done at the same time as the thermostat. I'm pretty much just going to drain the radaitor when I do the the thermostat to flush the fluid a bit. I have about 65k on the odo and don't know if it has been flushed. So, therefore, just need to know how fluid is needed to re-fill it when I'm done.