I never did. Lol. I drained & filled my 3.0 Cobra with AF every fall & in over 20 years never had an issue with freeze up or corrosion. I live in snow country & wind chill temps at night can drop to -25 or even lower.A lot of people do not understand the benefit of filling the block with antifreeze. They think it unnecessary.....well it is, if you are positive you got all the water out of the block. So, do you feel lucky?