I've never let the fluid sit in the sun to remove bubbles before, I just pour it slowly in to the MC and try to not create any excessive bubbles while bleeding. I've never really had a problem with a spongy pedal at all, either. That may have something to do with the 1-1/32" MC more than anything, but I did notice an improvement in pedal feel when I swapped the front hoses to braided stainless units.
As for compatibility, I used to keep a plastic Coke bottle in my garage that was half full of a 50:50 mix of used DOT3 and DOT5 fluids. Periodically, I would shake up the bottle and see if anything would ever happen to the mix. The only thing that really happened was that the two fluids would be mixed up in to a frothy mix for a while, but within a couple minutes you could see a distinct layer between the two. After an hour or so, there were no visible bubbles in the silicone fluid, and both were nearly clear again. Never saw any trace of goo, sludge, crud, or corruption in the bottle. DOT regulations require that the brake fluids be compatible. The following is an excerpt from the 49th Code of Federal Regulations, Section 571, Federal Motor Vehicle Safety Standards, Subsection 6.10
Quote:
S6.10 Compatibility. The compatibility of a brake fluid with other brake fluids shall be evaluated by running one test sample according to the following procedure.
S6.10.1 Summary of the procedure.
Brake fluid is mixed with an equal volume of SAE RM-66-04 Compatibility Fluid, then tested in the same way as for water tolerance (S6.9) except that the bubble flow time is not measured. This test is an indication of the compatibility of the test fluid with other motor vehicle brake fluids at both high and low temperatures.
S6.10.2 Apparatus and materials.
(a) Centrifuge tube. See S7.5.1(a).
(b) Centrifuge. See S7.5.1(b).
(c) Cold Chamber. See S6.7.2(b)
(d) Oven. See S6.9.2(d)
(e) SAE RM-66-04 Compatibility Fluid. As described in appendix B of SAE Standard J1703 JAN 1995 ``Motor Vehicle Brake Fluid.'' (SAE RM-66-03 Compatibility Fluid as described in appendix A of SAE Standard J1703 NOV83, ``Motor Vehicle Brake Fluid,'' November 1983, may be used in place of SAE RM-66-04 until January 1, 1995.)
S6.10.3 Procedure.
(a) At low temperature.
Mix 50 [plusmn]0.5 mL of brake fluid with 50 [plusmn]0.5 mL of SAE RM-66-04 Compatibility Fluid. Pour this mixture into a centrifuge tube and stopper with a clean dry cork. Place tube in the cold chamber maintained at minus 40[deg] [plusmn]2 [deg]C. (minus 40[deg] [plusmn]4 [deg]F). After 24 [plusmn]2 hours, remove tube, quickly wipe with a clean lint-free cloth saturated with ethanol (isopropanol when testing DOT 5 fluids) or acetone. Examine the test specimen for evidence of slugging, sedimentation, or crystallization. Test fluids, except DOT 5 SBBF, shall be examined for stratification.
Obviously, mixing fluids diminishes the benefit the higher-rated fluid.
Clair
