It is possible to use dimethyl silicone oil in windshield washer fluid with 30% alcohol content, but dispersion is a key consideration: dimethyl silicone oil is insoluble in water and alcohols (such as methanol/ethanol/isopropanol). Directly adding it to the windshield washer fluid containing 30% alcohol will cause stratification and floating, making uniform dispersion impossible. Therefore, you need to choose emulsified dimethyl silicone oil (pre-emulsified to form a water/alcohol dispersion) or use it with an emulsifier to ensure stability.
Recommended Viscosity and Reasons
The core functions of dimethyl silicone oil in windshield washer fluid are usually defoaming, lubricating wiper blades, and mild anti-fogging. It is recommended to select ultra-low viscosity dimethyl silicone oil, specifically:
- First choice: 5cst or 10cst: These two ultra-low viscosity dimethyl silicone oils have excellent fluidity. After emulsification, they can be uniformly dispersed in the windshield washer fluid system without affecting glass transparency. They have good defoaming effects (low-viscosity silicone oil is an excellent defoamer) and can lubricate wiper rubber strips to reduce abnormal noise. Moreover, they will not cause oil film residue on the glass due to excessively high viscosity.
- Second choice: 20cst: If slightly stronger lubrication or anti-fogging effects are needed, 20cst is also acceptable, but sufficient emulsification must be ensured to avoid residue. It is not recommended to use silicone oil with a viscosity higher than 50cst, as it may easily cause oil film residue on the glass surface, affect visibility, and significantly increase dispersion difficulty.
Usage Precautions
- Emulsification is a must: Pure dimethyl silicone oil cannot be dispersed. You need to purchase "silicone oil emulsion" (such as a silicone oil emulsion with 30% active ingredient) or mix silicone oil with emulsifiers such as Tween-80 or Span-60 for emulsification before adding.
- Control the addition amount: The recommended addition amount is 0.1%-0.5% of the total volume of the windshield washer fluid. Excessive addition is prone to generating oil films.
- Compatibility test: First mix in a small proportion (e.g., 100ml windshield washer fluid + 0.2ml silicone oil emulsion), and observe for 24 hours whether stratification or turbidity occurs to ensure stability.
Summary
- Dimethyl silicone oil can be used in windshield washer fluid with 30% alcohol content, but emulsified types must be selected.
- 5cst or 10cst ultra-low viscosity is preferred, balancing defoaming, lubrication, and transparency.
- The key is to ensure uniform dispersion of silicone oil to avoid residue affecting visibility.
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