What type of brake fluid Wilwood EXP 600 or DOT 5.1??

[txboiler]

I am nearing the point of bleeding the brakes have been reviewing pros and cons of brake fluid types. I am trying to decide between a Dot 4 and Dot 5.1 fluid.

I have Wilwood system and in the manual it recommends Wilwood Hi temp 570 fluid for "non severe or sustained hi heat operation". I don't plan on tracking the car but the cost difference between the Hi Temp 570 and the Wilwood EXP 600 is minimal compared to the hassle of flushing the system and rebleeding if (err...when) I decide to take it to a track day.

My understanding of The may difference between HiTemp 570 (dot 3) and Exp 600 (dot 4) are the viscosity dry and wet boiling points. Exp is the better choice sounds to be the better choice.... but the Wilwood manual also references that Dot 3, Dot 4 or Dot 5.1 can be used for performance driving. My understanding of Dot 5.1 is that it is compatible with poly-glycol (dot 3 and 4) and because it is silicone based it resists rust better, lasts longer, and wont eat paint. But since it is not hydroscopic it wont absorb moisture in the system and silicone based systems can be more difficult to bleed.

I am probably thinking too much about this and I am leaning toward the Exp 600 (dot 4) instead of the Dot5.1....what are others using and why?

[totem]

Dot 5.1 is also glycol based (unlike dot 5 which is silicone and should be avoided).

My understanding is that Wilwood race fluid have a higher dry boiling point but would degrade below dot 4/5.1 when old and "wet".

Since I track my car and refresh fluid every years, I use Wilwood race for it’s dry performance (or any performance fluid easily available, I’m not picky).

If you’re planning to keep the same fluid forever, I suggest 5.1 as it would have better "wet"/old performance.

[NAZ]

You're getting the DOT 5 & 5.1 brake fluids mixed up. DOT 5.1 is a glycol based fluid and DOT 5 is silicone based. DOT 5 & DOT 5.1 both have the same minimum dry boiling point (356F) but act very different and are not compatible. DOT 3, 4, and 5.1 are glycol based (glycol is an organic compound in the alcohol family) but DOT 5.1 should not be mixed with DOT 3 or 4. So if you start with DOT 4 and want to go to DOT 5.1, plan on flushing the system.

I use the Wilwood EXP 600 in my drag race car and it works good for that application. It has a dry boiling point of 594F and my brakes generate a calculated 864F stopping from 150 MPH, most of that heat is concentrated in the rotor and ~18% of that heat is immediately absorbed in the surrounding air. I reckon I could get away with using a garden variety DOT 4 with a dry boiling point of 311F but have never tried it.

But no matter which glycol fluid you choose, make sure your reservoir is not open directly to atmosphere as the dry boiling point of your fluid will immediately start diminish due to water absorption from the atmosphere. A good reservoir will have a flexible membrane between the fluid and the vent in the cap. Many reservoirs simply have a vent hole and that allows glycol based fluids to absorb water vapor from the air. This is the same reason you want to buy and store brake fluid in small containers.

[txboiler]

Thanks for the Clarification; i appreciate it