Oil is always a hot topic with engine builders. Its just another one of those things that has personal preference. I personally would run nothing but the 15w40 that Mercury Racing suggests while the motor is under warranty. After that, most of my customers either run synthetic 15-50 or conventional 20-50 racing oil. Either Mobil 1, Castrol or Valvoline. Once a motor is thoroughly broken in, I really like synthetic oil, Such as Mobil 1 15-50. I have had really good results with it. I have personally never run the Royal Purple, so I cannot comment.
Some people will say that synthetic oil is more prone to leaks, and I would have to agree to some extent, but with the one piece rear main seal and the nice job that Mercury does on their gaskets, I am not hesitant at all to run a synthetic oil in a 525. Does it make a power difference? I have never ran a test, but I will say that a well built motor that runs on synthetic oil looks very nice at overhaul time. If you plan on keeping your 525 for a few years, your synthetic oil investment may pay for itself. Just MHO.
thanx....I plan on keepin it for a while and hopefully soon have you put the whipple on it....I am in sand and gravel trucking and work is slow so I have to pull the belt real tight..no xtra spending for now..
I definately want to run a synthetic, I will check into the mobile.. I am a castrol man. what do you think of the syntec?.I run it in my jeep with no probs..I also run lucas in everything Ive got..I love that stuff..Has given my Peterbilt lots of xtra miles...