This is an old topic, but I’ll reitterate some of the points that have been expounded on in the past.
STP gets a lot of credit for having the necessary zinc compounds or zddp to deter cam and lifter wear on flat tappet camshafts but upon examining the MSDS for the product, you’ll find that these compounds are minimal and will not boost Zinc Dialkyl Dithio Phosphate (zinc for short) levels in API SL or API SM oils to the API SJ and earlier levels. In fact, it barely supplements the amounts present in the earlier API SJ and earlier oils. But in STP’s defense, it was not originally formulated to provide these additional wear additives and the formulation has not been adjusted (based on the latest MSDS) to supplement the Zinc wear compounds that have been removed from the API SL and API SM oils. But there are a multitude of oil additives on the market now that will provide the required additional amounts of zinc (Zinc Dialkyl Dithio Phosphate) wear compounds to the API SM oils that are 30W and less. If the oil viscosity is over 30W, then the required amounts are still there at the earlier levels and were never removed. Some of this info was mentioned almost a year ago on page one of this particular thread.
.
STP MSDS Link
.
What must be remembered is that the mandate for zddp reduction was not to reduce the zinc but to reduce the phosphate compounds that are present in the oil. It’s the phosphate that is a perceived problem for the catalytic converters and it is the phosphate that was mandated to be reduced. The phosphate is the component which is attracted to the heat from a metal to metal contact and the zinc simply follows the phosphate around and attaches itself as an anti-wear agent to wherever the heat is being generated as a result of the any friction being generated. With the mandate to reduce the phosphate, the zinc amount itself had to be reduced as the two are partners or symbiotic in their relationship. This is the simple explanation.
.
For those who are unfamiliar with doing a search on the site, here are links to past threads in which to bring newbies up to speed. But by all means do a seach for zinc or zddp to bring up even more on the subject as it’s been covered extensively over the last couple of years on this site and others and much longer than that if you include the old YBF site.
http://forums.y-blocksforever.com/Topic8508-3.aspx
http://forums.y-blocksforever.com/Topic1528-3.aspx
.
The search function is found at the top and upper right of each page. Give it a whirl.
Lorena, Texas (South of Waco)