OT- Coax for ground wire?

[W8JH]

I have learned quite a bit about grounding from K9YC and others on the list over the years and thank you all for making my shack a better place.

I have been tying together outside grounds where antennas enter the house back to the service ground as part of my improvements and have run out of heavy wire to do so.  I do have some old RG 8X or 213 around and have been thinking about using that for grounding.  My questions are:
1.  Good idea/bad idea?
2.  Should I use just the shield or is there any downside to bonding the shield and center conductor at each end?

Thanks in advance for any advice offered.

73,

Joe, W8JH
K3 1713, KPA 132