The major difference is that DOT5 is silicon based. You should not mix DOT5 with any other type. In older sytems it has more of a tendency to creep past the seals, leading to leaks. On the plus side it doesn't absorb water from the atmosphere like the other kinds do. And I believe it has a higher boiling point which is essential in modern systems where some quite exciting temperatures are generated.
DOT4 is simply an improvement on DOT3 whilst still using the same basic technique. If you suspect you have DOT3 then there is no problem with changing it out for DOT4. There isn't the same creep problem you can get with DOT5, HOWEVER, if you have really crappy fluid in there once it's all bled and ready to go you will have higher pressures in the system which can be the last straw for tired old seals.
If you are planning on switching to DOT5 (which doesn't attack paintwork apparently, which is why a lot of custom builders prfer it) from one of the others, you really should strip and clean the whole system, and pay close attention to the condition of the seals.
A good idea is to ring the tech guy from the manufacturer if you have a specific question.
Posted on Jun 17, 2003, 7:21 AM from IP address 62.30.85.24
