I read through all the posts, and realized that some of what I said may have been confusing. I will try and explain with a little more depth. First my comment on Shell Rotella not being what it used to be. I was referring to that oils film strenth. It has decreased by more than 20,000 psi in the last two years. However even at that level it it is still comparable to other brands. Now the additive package in that oil is still very good. The friction modifiers they use are still more than up to the task of protecting your flat tappet diesel engine. With that out of the way I will begin to explain my posts concerning the addition of ZDDP additive to modern oils. Back when oil companies first began producing lubricating oils there were no viscosity or friction modifiers in their oils. They where just plain old refined base stocks. When car companies began to build engines that demanded better lubrication the oil companies began to use friction modifiers in their oils. One of the main friction modifiers was ZDDP. Why, because it was cheap, plentiful, and it did the job well. All up until the late 90's when the EPA began to put the hurts to that game. From then until I believe 2008 (I'm not sure about the date) oil companies were forced to SLOWLY remove the ZDDP from their API listed oils. I capitalized slowly because this is where problems began. Oil companies believed the engines could easily survive with most of the ZDDP removed from their oils, and they were right as long as those engines were modern roller type engines. The fact was as the ZDDP was being removed almost nothing else was being added to help out older flat tappet engines. This is when everyone started to hear about ZDDP additives and how they were needed in flat tappet engines. That was true. If you added ZDDP to those oils that had most of the ZDDP removed then you were helping your engine out. You were just adding back what was being removed. However now that the EPA has mandated that all ZDDP be removed from API listed oils the oil manufacturers have had to turn to a different friction modifier. This is where the problem starts. This new more expensive, and better friction modifier is not compatible with the ZDDP. When mixed these elements begin to bond and negate each other's lubricating properties. If you are running an oil that is 15+ years old then you can still used the ZDDP additives. I personally don't have any that are that old, so I'm going to assume that everyone here is running a modern oil. These modern oils with their new better friction modifiers are more than up to the task of protecting you flat tappet diesel engines. I hope everyone reads this post in detail. If you have any queations please feel free to ask. I have spent more than four years researching oil, talking to big oil's chemists, and engineers, and doing the simple science myself. Please, I may one day wish to buy one of your engines. I don't want to buy one that been all screwed up.
