How long does the antiwear plating last?
Is oil tested to maintain the antiwear properties for a certain number of miles, time, cold starts, etc without being warmed up to refresh the plating?
Is there a point of diminishing returns where a higher level of ZDDP, Moly, etc doesn’t necessarily equate to a higher level of protection by cold start antiwear plating? What are those limits?
I’m going to give you a non answer, answer:
It depends!
The longest test I could find, was done for 500 hours. And the plating was still there and this was bearing test.
This particular test, was also done at room temperature and air exposed. It was also testing the various alcohol chain lengths of ZDDP for friction properties. So is it directly an engine? No.
So let’s look at other things… let’s take when you should pickle an aircraft engine. Different manufacturers say different things, but generally they recommend using a pickling fluid if you’re going to be inactive for over 30 days. A note on this that is very important, aircraft oils are very, very typically ashless oils - like 99% of them. Which means no ZDDP. (And yes, they’re flat tappet too! Different thread.) So they use other antiwears that, may or may not be as good / effective / etc.
Some aircraft engine manufacturers will extend when you should pickle an engine if you have varnish build up. As, that varnish will protect your engine as well from R&O.
So we can take this for a lower limits however, an essentially uncoated engine, that has never had ZDDP or essentially, other PCEO anti wear & preventatives - is 30 days, sometimes more.
Now let’s look at the other direction. A major bearing manufacturer uses Quaker Chemical’s 5856 BFT1 as their rust prevention product. This is a 1 year rust protection product that is applied at room temperature in a thin coat. Does it have ZDDP in it? No. It’s a specific made rust prevention product. Without going into details that I may, or may not be able to say, it’s a very simple product. They (Quaker) says it’s good for a year to prevent rust once applied in normal storage situations.
Alright. Now let’s look at your engine: Without starting, it’s going to do very little “breathing” - and unless it’s sitting outside, uncovered, your direct chances of moisture getting in are slim. Indirect through humidity changes are what you’re fighting.
Other things to think about: Does your engine have any coatings on the inside from the factory? Metal finishes and such. What sort of material is your engine parts made from? Is there varnish build up in places that will add protection?
So, how long will ZDDP, et al, other antiwear and anti corrosion additives protect in your engine? Great question, no real good “this is it!” Answer. But certainly north of 30 days.
On the maximum side? Depends on too many conditions to say for sure. But my guess is north of a year or more. (Personal guess.)