DOT 2 / DOT 3 brake fluid mix....
 

When I bought my Benz I was happy to see a MB battery and new MB brake master cylinder. As well as a few other new parts.

But with green goo installed for coolant, I am worried that DOT 3 may have been used. The car calls for DOT 2.

Can I assume they should not be mix? And if not, is there a way to tell them apart? The current fluid color is a light gold.

I have a very, very slow leak. I finally found it doing the ball joint but do not have the time or luxury to rebuild the calipers. And the fluid is starting to get lower than I care for. Need to top it off until I do all the brakes.

Is this on your 91 SEL? If so it calls for DOT4 brake fluid. DOT3 is compatible, but has a lower boiling point. If the fluid is a light gold color it was changed recently. In the springtime flush the whole system out for DOT4.

For topping up now DOT3 will be fine. But, I'd worry that the leaky caliper could fail suddenly. I'd consider replacing it now and flushing the whole system out for DOT4 (followed by a flush every other year).

-J

Ah.. sorry. Thought it was DOT2. Thanks much. I know, the caliper may go so I may just get two front rebuilds. Ideally I want to replace/rebuild all four and flush the lines/ABS at once. My pads appear new, that is probably the only reason the caliper has not failed. The boot has little room to move.

There is no way to know if you are running dot 3 or 4 by just looking at it. I would assume it is dot 4 and top up with dot 4. If you are worried about the brake fluid you can change it out for known dot 4 before the heat of summer, so you can be sure of using the higher boiling fluid when the danger from overheated brakes is at it's max.