Savage 写了： 2024年 1月 22日 20:32
尼玛我说了，版上90%的人都搞不清。结果连丰田专家奥托桑也迷糊了
我知道答案了，Google bard回答了我的问题。油在低温的确是粘稠的，5w30，这种违反常识的数字是添加剂造成的。
I have question about engine oil grade, 5w30 oil, why the viscosity index is high at high temperature as 30 while viscosity index is low at low temperature as 5. I think oil visocity is lower when temperature is high
You are absolutely correct that in general, the viscosity of oil decreases (becomes thinner) as the temperature increases.
The behavior of the 5W-30 oil grade might seem counterintuitive because of the way multi-grade oils are designed and the way the viscosity index is used.
Key points to understand about 5W-30 oil:
"5W" - Low-Temperature Behavior: The "5W" part of the oil grade indicates the oil's viscosity at low temperatures (W stands for "winter"). A lower number (5W) means the oil is designed to flow more easily at cold startup to quickly lubricate engine components during colder weather.
"30" - High-Temperature Behavior: The "30" part represents the oil's viscosity at operating temperatures (when the engine is fully warmed up). This number signifies how well the oil maintains its thickness and protective film at high temperatures.
Viscosity Index and Additives: Multi-grade oils like 5W-30 use special additives called viscosity index improvers. These additives help the oil behave differently at different temperatures:
At low temperatures, these additives allow the oil to flow more readily (hence the lower "5" in 5W-30).
At high temperatures, the additives help the oil resist thinning too much, maintaining a protective layer between engine parts (this results in the higher "30" number).
In summary:
The viscosity of 5W-30 oil does indeed become thinner at high temperatures like any other oil.
However, due to the additives used, the rate at which it thins is controlled.
The Viscosity Index is a measure of how much the oil's viscosity changes with temperature. A higher Viscosity Index (like in 5W-30) means the oil is better at maintaining a more consistent viscosity across a wider temperature range.
