That crunching sound is sand and crud. It may look clean but its not and if its been in the sand may never. I talked to some guys that rent bikes on the Galveston Seawall. They told me bike chains get full of sand even on the walkway. Their solution was to not use lubricant at all or if so very lightly. They also told me they replace chains often.
I did see one of their guys squirting a lube on a bike cart chain out of a Charcoal Light Fluid bottle. On asking he told me it was a mix of 50-50 ATF and Lighter Fluid. I asked him if it lubes and he turned and gave me a an unknowing shrug.
All in all it appears that rented bike chains on the beach don't last long...
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