If I'm not mistaken @70aarcuda buys whatever flavor Walmart oil he can find in the viscosity he wants and ads a 4-ounce vial of zddp.... Myself I'm more of the school of the manufacture didn't go through all that testing to make the perfect formula and then I go ahead and try and think I'm going to outsmart them and make my own formula LOL... There's got to be at least 10 other oils out there that also have zddp in them.. but I'm sure the one that you use is more easily gotten at the local parts store... With all that said I would be much more much More much More looking at your fan... and that's the reason I really want to know what temperature your cars at when you're going down the freeway for 20 minutes at a steady speed. If it's all good and dandy at speed for a long while that's going to be the catalyst for a circulation problem of air when you're not going at speed..