Less ZDDP = More engine wear?
The reduction of ZDDP in motor oils has caused many issues in flat tappet engines and a big stir in the classic car forum. Most V-8 engines in the muscle car era (cars built before 1975) came standard with a flat tappet camshaft and no catalytic converter. The flat tappet is, for the most part, flat on the bottom. Flat tappet cams are under a lot of pressure and require an extra oil additive for tight tolerances. Oil is the only thing between the lifter and camshaft lobe preventing them from welding each other together. Without sufficient lubrication during break-in and over long-term use, cams can suffer pitting, uneven lobes and severe wear patterns. So, in high performance or classic cars, opt for heavy-duty, performance or racing oils with higher levels of ZDDP that will provide flat tappet cams with anti-scuffing, anti-wear and oxidation inhibition.
Ok, so what about your basic passenger car? In the last decade or so, car manufacturers switched to more reliable, efficient roller camshafts for mass production. Because roller cams don’t require the same level of zinc protection as flat tappet cams, passenger car engines can afford a decrease in ZDDP. In fact, less ZDDP could actually be a good thing. Phosphorous—one of the main ingredients—is a poison to catalytic converters (fitted in most passenger cars since the mid-70s). Excessive ZDDP content will bond to the metal catalyst beads inside the converter rendering it useless as a pollution control device. See why the EPA wants to regulate the life requirement of the catalyst?
In order to meet API SM specifications, oil manufacturers must decrease ZDDP. Today’s modern passenger car oils contain other dedicated antioxidants to make up for the loss of ZDDP and resulting in a better overall product for consumers.
To sum up, less ZDDP is suitable for vehicles with roller cams and catalytic converters and bad for vehicles with flat tappet cams and no cat.