国内DOT 5.1便宜？我们这边基本不怎么买得到，贵得很哦。而且很少有厂家做这个。原因下面其实解释了。5.1就是一个标准而已，没有完全成为行业规范。行业规范还是3和4，而4的话其实达到5的标准以后就可以叫5.1了或者继续叫4也没人纠结。另一个角度说也不是4就一定比3好，满足4最低标准就可以叫4，但是人家3也有很牛逼沸点的但是就是要继续叫3；4和5.1之间也是类似关系。
或者另一种理解是你提到的motul RBF600是race grade的DOT4。跟平时说的DOT 3，4，5.1可以分开考虑，平时说的是street车用的标准而已。
StopTech : Balanced Brake Upgrades
One section discusses DOT 5.1 fluid:
Historically, DOT 5-level performance (specifically boiling points and viscosity) could only be achieved with silicone-based fluids. However, modern compounding has created glycol ether-based fluids which now meet DOT 5 bogeys in these key areas. Consequently, the DOT 5.1 moniker was created to differentiate between these two very different chemistries which both meet DOT 5 performance requirements.
In so many words, DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements. Because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern. In some circles, they are even referred to as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids because they are more similar to a conventional DOT 4 fluid by chemistry than they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially comprised of Borate Esters.
While it may not be obvious, the big advantage of the DOT 5.1 fluids is that they contain all of the nifty water-absorbing characteristics of the DOT 3 and DOT 4 fluids while simultaneously providing for very high boiling points and relatively stable viscosity over a wide range of temperatures. The best of all worlds, you could say. The table below sums it up quite nicely.
PROPERTY DOT 4 DOT 5 DOT 5.1
Dry BP 446 509 509
Wet BP 311 356 356
Dry BP (F)@ 0.0% H2O
Wet BP (F)@ 3.7% H2O
Chemical Composition
DOT 4 Glycol Ether / Borate
DOT 5 Ester Silicone Based
DOT 5.1 Glycol Ether / Borate Ester
http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid
【 在 tsinghuazjw 的大作中提到: 】
: 既然都是硼酸酯刹车油，成分比较类似，号称5.1可以兼容4
: 那像motul那个dot4的RBF600有何意义呢？随便一个dot5.1的油都能有差不多的沸点，价格还比它便宜
: 为啥还要开发那么高沸点的dot4呢？
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