School me on brake fluid
 

I chose regular DOT 3 hydraulic fluid for my brakes, clutch and accelerator systems. I recall my thinking was that because I would re-bleed/refresh every couple of years it would be fine, my worry being moisture buildup and therefore rust. I can't complain, except this scheduled maintenance when I took things apart I noticed black buildup on the cylinder bores of the clutch and accelerator slaves. The clutch is below the starter near the rear engine block (270 GMC) and the accelerator slave is under the exhaust manifold just forward of the exhaust pipe (there is a sheet metal heat baffle). Figuring the problem is heat, is there a better fluid to use? A higher heat DOT 3? What are the complications if I mix as there is still regular DOT 3 in the system?

Higher heat DOT3 is DOT4. When towing heavy trailers with a load, I have boiled the dot3 out of my system driving through hilly areas like medicine hat. Replaced it with DOT4 and never had another problem.

Thanks Rob. Does Dot 3 and Dot 4 mix? I've heard even traces of one will react with the other (and my system will have generous traces of Dot 3) unless I pull everything apart….yuk...). Or am I thinking silicon and synthetic?

3 and 4 are completely compatible. Dot 5 is where you will have not compatibility.