How big a screw up?

[Whitephrog]

Topped up my brake fluid yesterday. Accidentally pour about a thimble full of DOT 5 in with the DOT 4 already in the master cylinder. Is that going to cause me issue?

 

[BlueMax]

The mixture may gel and result in very poor braking; I would purge the system to prevent gelling with the DOT 4. Or you can just wait and see, but if it does gel you may have a more difficult time in removing the contaminated fluid.

 

[nomad]

If you haven't driven it and mixed the fluids I think I would try to suck out whats in the reservoir. Large syringe or oil removal gun that used to be carried by auto tool suppliers. Should not be to difficult.

Kurt.

 

[Guest]

I think even if he drove it a bit he'd be o.k to suck it out. I wonder if it sinks or floats in 4?

 

[RickB]

I've used a turkey baster to pull fluid out very successfully.
Just remove most of it and fill with dot 4 and you should be fine.

Remember to cover the area around the MC in case of drips.

 

[Healeysince59]

I have had a jar with a 50/50 mix of DOT4/DOT5 on my workbench for a couple of years. Periodically I give it a good shake. The 2 fluids mix for a while but separate over time. There is no sign of a Gel or any other nasty interaction. One interesting point is that the purple dye seems to have migrated from the DOT5 to the DOT 4. You need to make your own decisions when it comes to brakes but if it were mine, I wouldn't sweat a small amount of 5 in your system.

The 5 is less dense and floats on top of the 4 so it should be easy to use a baster to suck off most of it.

Marv J