Brake fluid, DOT 3 or 4?

[Davered00ss]

I just installed new Slotted/Cross drilled rotors & Hawk HPS pads. I want to change the fluid to DOT 4, but don't want to drain & fill the system.

Can I suck out the resivoe with a turkey baster and replace with DOT 4 before I pump the calipers back up? Can you mix DOT 3 with DOT 4?

[Ed Curtis]

I'm no expert on brakes but I wouldn't do this. I'm pretty sure it's not a problem to mix the flavors for brake fluids since it's just another type of hydraulic oil... I guess I'm leary when it comes to brakes.

Maybe get those Russel self bleeders and purge the whole hydraulic system with DOT 4 fluid.

Ed

[Davered00ss]

I'll wait until I change the lines to the Braides ones.

[Davered00ss]

I just found out Valvoline makes a brake fluid that can be mixed with DOT 3 or 4 and exceeds requirements for DOT 4. Something like 500 degree boiling point.

[kevin]

The dot 4 valvoline is decent stuff. If you are changing pads buy a quart and one of those cheap little bleeder kits from autozone (or some speed bleeders) and when you swap pads just do each caliper and flush the old stuff out.

[Lumpy]

I may be shooting from the hip, so take this with a grain of salt:biggrinbo


Dot 3, 4 and 5.1 are all glycol- based fluids and will readily mix.

without flushing the system, you will lose some of your performance gain, since any water, and/ or the old dot 3 will result in a mixture with a lower boiling point which defeats the purpose of what you're wanting to do.

IIRC the problems start when you introduce silicone (dot 5) fluids into the glycol systems... they don't play well together; and dot 5, although it offers a high boiling point, does not offer enough benefits to outweigh the disadvantages.



not that you asked, but my two bits:

1. use the el-cheapo O'reilly store-brand dot 3.
the difference in boiling points between dot 3 and dot 4 is less than 50 degrees. 3% water absorbed into your brake fluid, by comparison, will drop the boiling point by 100 degrees. no fluid will improve brake pedal feel, or reduce stopping distances.

if you keep your system flushed with clean fluid, dot 3 should be enough to do anything you want to do. it takes a lot of heavy braking to boil clean dot 3.

dot 4 could help with autocross ...which, I assume you do not do considering that you just purchased crossdrilled brake rotors.

2. if you just drive this car on the street, bleed a small bottle of O'reilly dot 3 through the system every time you change your oil. takes ten minutes with a plastic $40 mityvac. be sure to hit all four brake calipers, starting with the caliper farthest from the master cylinder and finishing with the caliper closest to it. (passenger rear-driver's rear-passenger front-driver's front. in that order.)

3. remember that the minute you break the foil seal on a bottle of brake fluid, it begins to absorb moisture from the atmosphere, even with the plastic cap on it. if you want maximum performance, always use a fresh bottle. if you really, really wanted to use a better fluid than standard dot 3, go to sam strano's website and order super blue ATE. it has a high wet boiling point, which is really what you want. it comes in blue, and amber, which makes flushing/bleeding the system easy. the steel bottle is also supposed to keep the fluid "dry" in storage.

Lumpy