In article ,
Scott Derrick wrote:
I have a pusher airplane with a nose oil cooler.

I am replacing the existing heavy hydraulic type(rubber/braided steel)
oil cooler lines with lighter metal lines. Either soft Aluminum or soft
copper 1/2 lines.

First question. I would like to use the lines as my ground return and
remove the 2 AWG wire I have now. Good idea?

*DAMN*STUPID* one!

Consider the cross-section area of #2 wire,
then compare with the cross-section area of the walls of the tubing.

Without considering what happens if/when a line _breaks_.

"Instant" spark across the gap, With a ready supply of fuel being delivered
to the scene.

Second question. Which would be better, or possibly which would be
worse and why? Copper or Aluminum.. Aluminum would be lighter but
copper offers a better ground return(less resistance). I have a big
engine and the starter needs all the current I can muster.

For the same current load, you need (minimum) 1 gauge larger wire, if AL,
vs what you need for Cu. That equates to circa 30% more material, by
volume. Which negates a fair bit of weight difference.

Your last statement *should* answer your question. for max current
transfer efficiency, use the best conductor you can, at the largest size
you can justify.



Scott