I'm quite mechanically inclined (formerly an auto mechanic and currently an engineer) but relatively new to cycling. Compared to other contexts I'm familiar with, I've noticed that bike chain lubricants, for example the Park Tool chain lube (https://www.amazon.com/Park-Tool-Synthetic-Blend-Bottle/dp/B000AOA290) or the Finish Line wet chain lube (https://www.amazon.com/Finish-Line-Bicycle-Chain-Lube/dp/B000WYCD5O?th=1) are very expensive per quantity compared to automotive lubricants. I'm wondering if anybody has extensively tried any of the following as bike chain lubricant:
-Automotive Transmission Fluid (ATF)
-Manual Transmission Fluid / Transfer Case Fluid / Gear Oil
-relatively "heavy" motor oil, ex. 10W-40
In my general experience I've found that ATF is usually the best lubricant for almost any purpose, for example I've found that ATF lubricates air tools better than air tool specific lubricants.
I'm planning on trying ATF out before I spring for another bottle of Park or Finish Line chain lube. Has anybody else tried any of the above for bike chain lubrication?