Effect of The Silicon Contamination

Jeff,
Most often, silicon is ingressed from the environment (dust, dirt, sand) into lube oil. As such (in a contamination particles form), and depending on their size, it will mess up you air entrainment and/or foaming characteristics, as would do non-silicon particles, too, because every particle in oil serves as a seed for air entrainment and foaming. Remedy: Add an efficient off-line filter, and let it loose 24/7, and monitor cleanliness and follow up with spectrometric analysis of Si, to see if there is any relationship. Also, add breather(s).
However, silicon can get in oil (in a dissolved form) through mixing with Si-based sealant, paint, and greases. Such contamination usually happen during an overhaul or other maintenance efforts. For example, if thrust bearing were replaced and preservative bearing grease (some are Si-based) was not sufficiently cleaned out, it would contaminate the entire oil in the tub. Such oil would now have unbalanced foaming additive, and would foam more. It can also screw up additive package if there are any sudden additives incompatibility issues. Remedy: I don’t know any short of replacing the oil, providing that this Si changed characteristics of oil to the degree that impedes operation. If there were not any adverse issues, then I would continue to operate with this oil, but would periodically check and track its level, and keep an eye on the performance of the oil.
Less often (I may say very rare, but it did happened before) oil is contaminated with Si if someone dumps some foreign oil containing high conc of Si into your lube oil.

Thanks very much John

How the anti foan additives works base on chemical or phisic reaction ? how it mechanism to preventing air entering

Hi JeffTurbo,

Noria have an article called Controlling Oil Aeration & Foam which gives a good explanation on how the antifoam works.

So If I use Synthetic Oil like Mobil SHC 630 can youl tell me , is the oil fully compatible with the silicone seal. I am afraid the high silicone contamination in the oil sources (until 75 ppm). Just from the Silicone seal

I believe that SHC is a PAO based product, so compatibility with silicone seals is satisfactory (but not recommended). You may want to check with Mobil, they should have a base oil vs seal material compatibility chart to confirm this.