Posted by Traveler on February 13, 01 at 14:24:15:
This has been copied from the HP Pickup forum in response to my question. NJCKZ71 is quite a brake expert. I asked why the two fulids he suggested for severe duty were better than Valvoling SynPower.
"Motul600 has even higher wet/dry boiling points and the better yet is the Castrol SRF which is synthetic and has a polymeric compound that actually absorbs water and maintains extremely high (the highest out there) wet and dry boiling points. This means you won't be changing it for years! Both also have much better fluid compressibilities than other fluids out there including the Valvoline product. Yes contrary to popular belief brake fluid is compressible and is a non-Newtonian fluid. Also, the boiling points and compressibility characterisitcs have been verified by independent laboratory tests.
I've had it in several vehicles, including my Tahoe and Pro-Street pickup for years with no decrease in performance. The fluid takes a lot of abuse stopping the blown 502 in my Pro-Street! It's been in my Z71 for 3.5 years too, and the fluid is still perfect and I tow a 6200 lb trailer everywhere with OEM rotors, drum, shoes, and Delco Durastop pads!
Motul is well known in the motorcycle world were brakes undergo extreme temperature and abuse. The Castrol SRF (Special Racing Fluid) was also designed for the extreme heat of racing and can be found standard on many exotic sports cars for good reason. Best of all, either fluid is compatible with the stock materials of GM's late model brake systems (i.e., no worries about seals). However, you pay for quality, Motul is about $15/pint and Castrol SRF $65/liter, but you won't find yourself flushing them out with every brake change either.
I've been using both since their introduction in radically enhanced vehicles (race cars, rods, etc.) and in underbraked stockers like GM's trucks and SUV's making many a customer extremely happy in the change of behavior. Toss on DOT-approved stainless-sheathed lines and a complete different behavior is found!"