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DOT 5 is silicone based, but from my understanding they can be mixed with DOT3 &4. The DOT won't leave it up to the end user to make that call whether they can be mixed or not, they are compatible correct? Please elaborate on pedal feel. Does the DOT 5 compress more than the glycol based 3 and 4? On a fresh system why would it be a disadvantage to run 5?
Jeff
DOT5 could cause some gelation or possibly be incompatible with the seals in the master cylinder as well. Chemicals that aren't intended to be mixed.
DOT5 can't absorb water or air from the fluid, it will not be absorbed and is more difficult to bleed, will not keep the water in suspension so any pools of water (there is moisture in the air) won't benefit from any protection the gylcol fluid could provide. You absolutely want the fluid to absorb it vs it pooling separately (like oil and water separate) This along with the slightly higher compressibility would make your pedal longer. It also will not flow through your ABS valves like the glycol fluid, so it will mess with the calibration at the very least.
Maybe I’m missing something but how can fluid become dirty, contaminated and have moisture if the system is closed? Now if you have a line brake then I say maybe.
The system is absolutely not closed. The master cylinder has venting in it in all cases so fluid can flow when there is a leak or a need for more volume (such as pumping). They are usually venting slits or small holes in the membrane that are hard to see. The dirt is usually either from pushing the pistons back in during a pad change OR some level of leeching from the rubber parts, or wear of the seals or bores.
