I have a '98 W210 wagon and just purchased the Motive Pressure bleeder tool and will use it to flush my brake fluid.

The old brake fluid in the reservoir is 2 years old but looks clear, new and the same color as fresh fluid I purchased.

My question is, if the color of the old and new fluid are the same, how will I know when the old fluid has been pushed through the system and new fluid is making its way out of the bleeder screw?

I seem to recall someone talking about a reasonable duration for the bleeder screw to be open that would ensure that all the old fluid was out (right-rear wheel).

Anyone have a magic number?

How about a PSI for pressure bleeder?

Thanks in advance.