Engine oil 2: Oil viscosity index
(引擎機油 2：機油黏度指數)
After a brief review of the use of engine oil, we will now move on to one of the most important concepts: oil viscosity index.
之前有大略簡單的提到引擎機油，我們現在要繼續進入到最重點觀念之一：
機油黏度指數
Oil viscosity index explained
(機油黏度說明)
Viscosity is simply the resistance of a fluid to flow. A higher viscosity implies a slower flow and a thicker fluid.
黏度，簡單說就是液體的流動狀況。高黏度表示液體流動漫並且較黏稠。
The viscosity changes with temperature to ensure protection and operability under all circumstances. Thus, the viscosity index measures the ability of an engine oil to resist becoming thinner at high temperatures.
黏度會隨著溫度變動以確保在任何情況下都能保護和運作。因此，黏度指數是測示
機油在高溫時能抵抗變稀薄的程度。
To be able to change the viscosity index, conventional oils incorporate additives, usually plastic polymers. Some synthetic oils are able to achieve this variation without additives.
為了可以改變黏度指數，傳統(礦物)油會結合添加劑，通常是plastic polymers(塑料聚合物)。有些合成油不需要添加劑就可以達到這些條件。
The SAE (Society of Automotive Engineers) established a numerical code to represent the viscosity of oil at both hot and cold temperatures.
SAE(汽車引擎工程師協會)建立了一個數列號碼去對照機油在冷/熱溫度時的黏度。
The number before the W represents the oil viscosity at lower temperatures, while the second number (after the W) indicates the viscosity at operating temperatures.
在W前的數字的對照機油在低溫時的黏度，而第2個數字(在W之後的數字)指的是引擎在運轉時的溫度。
For example, this means that 5W30 engine oil has less viscosity at lower and higher temperatures when compared to 10W40.
舉例來說，就是說5w30的引擎機油在低溫及高溫時的黏度比10w40低。
You should be aware of climate changes in order to keep your engine fully functional. Here you can see the recommended oil for each ambient temperature:
你應該察覺氣候的變動以維持你的引擎效能正常。以下你可以看到在不同溫度環境時推薦的機油黏度
Ambient temperature in ºC
If you are interested, you can see more information regarding SAE specifications here.
如果你有興趣，你可以在這個連結here上看到更多SAE規範的資訊 。
But be careful: transmission oils have a different SAE numbers. For example, a 75W90 transmission oil doesn’t have a higher viscosity than a 15W40.
但要注意：變速箱油屬於不同的SAE黏度數字。例如75w90變速箱油的黏度並不會比15w40高。
Oil specifications (機油規範)
Apart from the viscosity index, there are other factors to consider when choosing an engine oil for your vehicle.
除了黏度指數的部分，在你為車子選擇機油時還有其他因素需要考慮。
ACEA specifications (ACEA規範)
The ACEA (Association des Constructeurs Européens d’Automobiles) has its standard regarding the specifications of oils. They put oils through a series of tests, which get updated when new legislation, new technologies or other reasons demand change.
ACEA(歐洲車輛製造協會)關於機油有他們的標準規範。他們將機油透過一系列的測試，而這測試會依據新法規、新技術或其他因素需求並有所更新
The ACEA specifications cover passenger and commercial engines, divided into the following sections:
- A/B: Petrol and Diesel engines. They are usually combined in the specification. For example A3/B3 or A3/B4.
- C: Catalyst compatible oils, which also extend the DPF life.
- E: Heavy duty diesel engines
ACEA的規範包含汽車引擎及商用車引擎，分為幾個部分：
• A/B：汽油及柴油引擎。他們通常在規範裡是標示在一起。例如A3/B3 或A3/B4
• C：與觸媒器相容的機油，其中也延長DPF的壽命(連結DPF life)
• E：重級柴油引擎
You can find more details about the differences between all specifications in the
official ACEA PDF, specifically on page 4 and 5.
你也可以在(連結official ACEA PDF)看到所有規範之間不同的比較，特別是第4頁及第5頁。
API specifications (API的規範)
On the other hand, we have API (American Petroleum Institute) specifications. They use a two letter specification, dividing them into:
- S for Petrol engines
- C for Diesel engines
- F for modern Diesel engines (introduced in 2017): this new specification aims at reducing fuel consumption
另一方面，我們有API規範(美國石油協會)。他們是使用2個字母做為規範，分別是：
• S是汽油引擎
• C是柴油引擎
• F是新型的柴油引擎(2017年)：這個新規範主要針對減少燃油的使用
The second letter of the specification indicates its quality. The lowest quality is the letter A, and each letter after A represents better quality. For example, an API SN oil is better than an API SJ. As with ACEA specs, the specifications can be combined when the oil is suitable for both diesel and petrol engines. For example, an engine oil can be SM/CF.
You can learn more about API specifications on the API official site.
規範的第二個字是關於品質。品質最低的是英文字是A，隨著A之後的英文字品質也跟著變好。舉例來說，API SN的機油比API SJ好。就如ACEA的規範，當機油可同時用於柴油及汽油引擎時，這些規範可以跟並列使用。例如引擎機油的規範可寫為SM/CF。你可以從API的官方網站(連結official site)了解到更多關於API的規範。
Brand specifications (OEM, Original Equipment Manufacturer)
品牌規範(OEM汽車製造廠)
It can also happen that manufacturers create their own specific set of requirements for their engines. These oils meet SAE specifications but the manufacturers add some extra conditions. Consequently, the oil needs to pass extra tests like the Volkswagen VW 507 or the BMW Longlife 01.
規範也可以由引擎製造廠依照他們的引擎需求設立他們自己的規範。這些機油會符合SAE的規範，但製造廠會增加一些其他的條件。進而，機油需要同過其他的測試，例如Volkswagen VW 507 規範或是 BMW Longlife 01規範。