I refi my rental prop in 2010 and began depreciating closing costs,. I refi the same prop in 2016 with the same lender. Can I expense the unused depre from the 2010 refi?

Yes you can take a deduction for the remaining unamortized balance of your original refinance costs. These costs should be listed as an Intangible under your property asset section.

Dispose of the prior intangible asset in the asset section and indicate the date it was 'retired'. This should accelerate the remaining unamortized balance for this year.