Originally Posted By: d00df00d
Excellent questions.
Yes, I would love to know as well to what extent ZDDP works better in a hot oil than a lukewarm oil. It would be great if someonne could do a wear test of say a high ZDDP concoction oil at cold temp vs one kept above 170f.
I found this in a vw forum, and so yes it seems that zddp works best (or at all...) above scalding coffee temps if the word going around on the interwebbs is to be believed:
Quote:
The ZDDP issue relates to the sliding contact pressure exerted by the cam lobe on the flat tappet (follower) which in turn moves the pushrod and opens the valve. The stronger the valve springs, the higher the pressure needed to open the valves, and therefore the higher the sliding pressure placed on the flat tappets by the cam lobe. This sliding contact creates wear unless there is something to protect against that wear. ZDDP actually decomposes under the high temperature caused by the metal to metal contact, resulting in a microscopic coating on the tappet which protects it from further scuffing. You'll note that the Castrol guy in my article above talks about keeping the oil temperature above 80c if possible - this ensures that the temperature rise at the piont of a metal/metal contact increases the temperature at that point of contact to the decomposition temperature of the ZDDP. Cold oil will not "activate" the ZDDP protection.
Since the ZDDP is "sacrificial" (it gets used up), the amount of ZDDP still left at the point of the oil change is more significant than the amount contained in the fresh oil. The worry expressed by others about the reducing amount of ZDDP in fresh oil is really a worry about whether there will be any left to provide protection as the oil ages.
The VW engine does not spin especially fast, so it doesn't need particularly heavy valve springs, so the need for ZDDP to reduce scuffing is not as great as it would be for higher performance engines.
We change the oil in our VW engines at 3000 miles (5000km) which is more frequent than most other cars. The ZDDP has less time in which it is "used up".
Oils themselves have improved out of sight compared to the oils of 30 years ago.
The result is that the VW engine can still remain reasonably well protected from cam/tappet scuffing with the reduced levels of ZDDP in many oils.
But you still need SOME ZDDP in the oil - the VW engine DOES have flat tappets and the oil engineers have not found anything better than ZDDP to protect those flat tappets from scuffing wear.
