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I was using an ZDDP additive to the Valvoline 30 wt oil I have been using for my 51 "300", but I cant seem to find the same additive.( They changed the packaging.)( I Think. ) I have had no issues, but I know the car needs an oil change, so in a way I am in the same boat as the original poster of this thread.ie: not sure what way to go. I Like the ZDDP additive, and have had no issues. What ZDDP additive?

The blue bottle STP has ZDDP in it.
John

But is one bottle of STP enough? Also what is the weight of STP - straight 30W? ---40W?

I run Rotellla 15/40 and a quart of Lucas Oil Stablizer. My car has 123k. Original engine no rebuilds. It was making a little noise in the lifters. I started using the stablizer and the lifter noise is gone. It has 30lbs idling and 42lbs at highway speed (oil pressure)