Why can't dot5 brake fluid be used with ABS?
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gathermewool
Site Donor 2023
I don't know if there is a prohibition (I doubt there is.)
DOT5 CANNOT be mixed with what's in your Impreza, which is more important.
DOT5.1 OK
DOT5 - not OK
DOT5 CANNOT be mixed with what's in your Impreza, which is more important.
DOT5.1 OK
DOT5 - not OK
When agitated rapidly (such as the on/off cycling of ABS valves) silicone-based brake fluid foams excessively. Foaming causes the same behavior as if there were air in the lines...so once ABS engages, you're suddenly not stopping.
Edit: additional information
Silicone fluids dissolve air into solution and the rapid cycling of the ABS can release it as a gas.
Video of DOT 5 under vacuum, releasing dissolved air: https://www.youtube.com/watch?v=a9IWde0n0Cg
Edit: additional information
Silicone fluids dissolve air into solution and the rapid cycling of the ABS can release it as a gas.
Video of DOT 5 under vacuum, releasing dissolved air: https://www.youtube.com/watch?v=a9IWde0n0Cg
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Originally Posted By: Wampahoofus
When agitated rapidly (such as the on/off cycling of ABS valves) silicone-based brake fluid foams excessively. Foaming causes the same behavior as if there were air in the lines...so once ABS engages, you're suddenly not stopping.
Edit: additional information
Silicone fluids dissolve air into solution and the rapid cycling of the ABS can release it as a gas.
Video of DOT 5 under vacuum, releasing dissolved air: https://www.youtube.com/watch?v=a9IWde0n0Cg
That's the kind of answer I was looking for. Thanks!
When agitated rapidly (such as the on/off cycling of ABS valves) silicone-based brake fluid foams excessively. Foaming causes the same behavior as if there were air in the lines...so once ABS engages, you're suddenly not stopping.
Edit: additional information
Silicone fluids dissolve air into solution and the rapid cycling of the ABS can release it as a gas.
Video of DOT 5 under vacuum, releasing dissolved air: https://www.youtube.com/watch?v=a9IWde0n0Cg
That's the kind of answer I was looking for. Thanks!
MolaKule
Staff member
There is also a paper on Brake Fluids if you are interested:
http://www.bobistheoilguy.com/forums/ubb...ids#Post3076040
http://www.bobistheoilguy.com/forums/ubb...ids#Post3076040
The rubber components that are compatible with DOT3/4/5.1 are usually not compatible with DOT5. That would include the components inside the ABS module.
Originally Posted By: MolaKule
If you mix a higher boiling point fluid with a lower boiling point fluid, you lower the overall boiling point of the resultant mix.
Not quite correct. The boiling point of the resultant mix in this case will be somewhere between the boiling point of the lowest boiling point fluid and the highest boiling point fluid. It is perfectly fine to use DOT4 where DOT3 is specified, but not the other way around. That's why Valvoline has brake fluid container labeled as DOT3 & DOT4 brake fluid.
The reason it is communicated to the public not to mix the two fluids is precisely because manufactures don't want that to be interpreted as DOT3 can be used in place of DOT4.
If you mix a higher boiling point fluid with a lower boiling point fluid, you lower the overall boiling point of the resultant mix.
Not quite correct. The boiling point of the resultant mix in this case will be somewhere between the boiling point of the lowest boiling point fluid and the highest boiling point fluid. It is perfectly fine to use DOT4 where DOT3 is specified, but not the other way around. That's why Valvoline has brake fluid container labeled as DOT3 & DOT4 brake fluid.
The reason it is communicated to the public not to mix the two fluids is precisely because manufactures don't want that to be interpreted as DOT3 can be used in place of DOT4.
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