[ASKED] Brake fluid and track events
 

The owners manual states that, for track events, the factory brake fluid needs to be replaced with qualified high performance brake fluid with a dry boiling point greater than 279 Celsius. It also states that one should replace the track brake fluid with factory brake fluid before driving on public roads. Why is this? I read a blog post from someone suggesting that high performance brake fluid absorbs moisture quicker and consequently can lead to increased corrosion in the braking system compared to regular brake fluid, but I've also seen posts from others who use high performance brake fluid for all driving and don't report any issues. What bad things could happen from using high performance brake fluid for daily driving on public roads? Or, is the issue really that any brake fluid, once subjected to a day on the track, needs to be changed as soon as possible, and that there's nothing wrong with using high-performance brake fluid on the street?

It's true that DOT4 fluid can absorb water at a quicker rate than DOT3. However I keep DOT4 (specifically Castrol SRF) fluid in my C7 year round and flush the system completely once a year and bleed when necessary. It's not my daily, only my track toy and weekend cruiser so I'm not racking up huge miles. About 1,000 track miles plus 4,000 street miles a year. I'm sure the reason they suggest reverting back to the normal OEM fill is because most people don't flush their brake system enough and as a result DOT4 will need replacing sooner than DOT3.

Just ran the stock fluid with track pads at Gingerman and had no issue with the fluid at all, not even a hint of fade (2017 Grand Sport). I changed my fluid to ever-increasingly-better DOT-4 in my 2015 Z51 and until I got to Castrol SRF, KNS Rotors and Raybestos pads, never fully conquered brake fade. I never even gave the stock fluid a chance in that car, though. Not sure if I should chance leaving it in at Road America next month ... that track's a brake killer.

Thought it was DOT5 that is for track - that's what I remember them telling us at Ron Fellows

They didn't tell you that.

I'm pretty sure Ron Fellows didn't even change from stock fluid, if I remember correctly (been 2 1/2 years). I remember being amazed that they'd use up the stock pads on stock fluid, and then change to Hawk pads, but that was it, and you got no fade in their cars.

They indicated during a recent track event week that they only did two things to the stock vehicles: 1. aligned it for the track according to the manual and 2. replaced the DOT 4 with DOT 5 brake fluid. That is what I recall.

No! The do not use DOT 5!!!! They change from DOT3 OEM to DOT 4 high temp fluid.

And —

3) Adjust tire pressures. Usually take some out cold due to the heat in Pahrump

4). IMPORTANT — Change the oil to a higher temp Mobil 1 per the manual. I think to 15W50 from 5W50

I was there in Sept.

The hygroscopicity depends on the particular fluid! It is not a universal characteristic of DOT 4 over DOT 3!

This is link to a multipage detailed ABC's of brake fluid by Toque Racing Brake Fluid: http://torquebrakefluid.com/abc.html

Quoting what they say about DOT 4-

DOT 4:
Also containing glycol, the SAE J1704 specification considers DOT 4 to be a borate ester base fluid and is also clear to amber in color. While somewhat less hygroscopic than DOT 3, it still absorbs moisture, with a minimum dry boiling point of 446°F (230°C) and minimum wet boiling point of 311°F (155°C).

Tadge in his answer to the question of why their recommendation to change brake fluid before an after tracking defined racing brake fluids, (often rated as DOT 4 since they exceed its higher dry/wet boing point) are more hygroscopic.

Dot 4 "standard" brake fluid may be somewhat less susceptible to water absorption. Racing brake fluids however they are formulated to have higher dry and wet boiling points that can also make them more hydroscopic!

Hydroscopicity is not a parameter provided by the brake fluid manufacturers. Each varies in that regard.

They definitely change the pads, at least for level 2. The swapped cars for me halfway throught he day and I noted the brakes changed. He said they use Hawk X pads and they were considering trying Hawk Y pads. Can't remember which ones.