I have three containers of the same motor oil, but different weights. They are dated 2018, 2016, 2015. The 15 smells odd, but not sure if it was like that when new? I put it in the engine for 15 minutes, then shut down. The 2016 there is not enough to do an oil shange. The 2018 is still a sealed gallon, enough to do a change. I googled, but went in circles. Does anyone here know factually if the 2016 is still usable?