A plain steel washer is not designed for sealing. It's designed to give a bolt head a surface to turn on while being tightened.Good thread thus far. Do some cars drain plug just use a regular steel zinc-plated flat washer? In the past (when I was still physically able to change my oil) it looked like an ordinary steel flat washer to me (on my 1996 Jeep 4L).
One reason is that they are as much as a dollar a seal.Crush type washers deform to effect a seal. Additionally, the deformation may work harden the (metal) washer which along with the initial deformation, may affect the washer's ability to seal again. Most of what I own use aluminum or copper crush washers and I generally replace them each time, but I have smoothed and re-annealed a few in a pinch. At ~$1 a seal tops, cannot see a reason to not replace them.
and whether you use foot pounds or inch pounds too....Let's start a poll: For those that replace their washer every oil change, do you use a torque wrench to tighten the drain bolt?