I have an 03 HPDI 250. I have been running yammalube ever since buying the boat used over a year ago. I was told to always use yamma lube and ring free. I have recently been reading about other oils. I have a case of Pennzoil Premium Blend, not the synthetic, that I would like to use since I have 3 gallons of it and will save a few bones. This is TCW-3 certified. Will it hurt my motor at all being an older motor. How far down to I use my yammalube in the tank before adding the oil. I want to use it, but I am really cautious about causing problems. Also, if ok to start using it, will I be able to switch back to yamma lube since not a synthetic oil. Thanks in advance