The silicone oil in the shock-resistant pressure gauge turns yellow, which is actually quite common and not complicated. Simply put, there are two main reasons: one is the nitrile rubber in the case, and the other is sun exposure. These two factors must exist simultaneously for the silicone oil to turn yellow. Sometimes, there may be other accidental factors that cause discoloration.
Many users found that the silicone oil in the shock-resistant pressure gauge they bought turned yellow after a period of use. They not only wanted to replace the yellowed silicone oil, but also wanted the manufacturer that produced the pressure gauge to identify the problem and make improvements.
Specifically, nitrile rubber may turn yellow when exposed to the sun, but this will not happen if it is replaced with silicone rubber or fluororubber.

The reasons for the discoloration of silicone oil may be as follows:
1. The pressure gauge may turn yellow due to the exposure to the sun, which can cause the silicone oil inside to turn yellow.
2. If the pressure gauge is used at high temperature, the silicone oil may also turn yellow.
3. If the pressure gauge is not used for a long time, the silicone oil may turn yellow.
4. The dial or pointer may fade and fall into the silicone oil, which can also turn yellow.
5. The quality of each batch of silicone oil is different, and sometimes there are problems with the silicone oil itself, which can also lead to yellowing.
6. The silicone oil may turn yellow when it comes into contact with the rubber inside the watch case.
7. Silicon oil can also turn yellow when it reacts with other substances in the watch case, such as gasoline, alcohol, and glycerin.
8. Sometimes, these factors may occur simultaneously, causing the silicone oil to turn yellow.

Therefore, if you want to make silicone oil less prone to yellowing, you may have to start from these aspects, such as improving rubber materials, avoiding high temperatures and direct sunlight, or improving the formula of silicone oil.