What zinc level do you think is best for our mod motors?
I wish I really knew. As far as I know none of our motors have experienced catastrophic camshaft failure like the older flat tappet (lifter) push rod motors have. But, they didn't know modern oils would eat up their cam shafts either until it started happening under the SM standard (800 ppm phosphorus maximum).
Roller lifters and overhead cams do not require as much of a zinc-phosphorus barrier. Most of the experts said they thought 800 ppm of phosphorus (zinc always is slightly higher) was good for these engines. I ran Quaker State full-synthetic 5w30 under the SM standard for years. After 160,000 miles my engine showed very little wear. Even the timing chain guides showed little wear. But under the SN standard they have reduced the ZDDP content even more (
March 2013 - Test Results for AP).
No one will know how low is too low until we start having cam shaft failures. One expert said something that made a lot of sense to me. He recommend that you run the level of ZDDP that was in oil at the time the motor was made. For us that would be the SJ and SL standards which had around 1000 ppm phosphorus (
http://www.pqiamerica.com/TIMELINE 5-23-2013rv23.pdf).
I didn't start worrying about this until I found that the Mobile 1 Advanced Fuel Economy 0w30 I was using dropped their level to 650 ppm phosphorus under the SN standard. That was when I started using 1/2 bottle of Reslone 3X Concentrate ZDDP to my oil. They recommend a full bottle for 1995 and older motors. In 5 quarts of oil it would bring the ZDDP up to around 1400 ppm for flat tappet motors. And, they recommend 1/2 bottle for 1996-2004 motors. If I did the calculations correctly in 6 quarts of oil that would bring that 650 ppm up to around 950-1000 ppm.
I don't want to be the first to find out there is insufficient ZDDP for our motors in modern oils. I'll let others have that honor. Reslone's ZDDP additive costs less than $10 at Advanced Auto. That is cheap insurance if you are running a 20 or 30 grade oil. I intend to continue using it in my F150. It only has 80,000 miles. But for my 180,000 Mustang I think I'll switch to 0w40 European blend. It costs the same as 0w30 at Walmart so if you need the heavier oil you get the ZDDP for free.
To answer your question my gut feel is that 800 ppm is OK but 1000 ppm is better.
---------- Post added at 04:04 PM ---------- Previous post was at 03:54 PM ----------
I used 10w in all my cars, with 135k miles there's probably enough tolerances loose to where it shouldn't matter. In my opinion 5w20 I wouldn't use in anything especially when it gets hot
They have made huge advances in oil technology since the '60s. Why are you sacrificing better cold start protection? Again, a cold start is any start below the normal 212*F operating temperature. It can be 110*F in the shade when you first start the motor and its still a cold start. The oil is too think to flow. You can get the same "hot" engine protection and better cold start protection by using a 5w30 or 0w30 oil. I'm of the opposite opinion. I wouldn't run 10x-anything in my motors.
