Checking up on the dealer brake fluid recommendation
 

On my last visit, the dealer recommended changing the brake fluid. I declined because A) I'm at 24k miles and the service schedule doesn't indicate it and B) I had new rotors, pads and DOT 4 (Motul RBF 660) put in around 10K miles ago. Since i'm all street driving (daily commute and some weekend fun), when do I need to think about new fluid and should I go back to OEM fluid or stay with the DOT 4)

I would probably do new fluid in 2 or 3 years. Stay with DOT 4.

A trusted source told me that GM specifies DOT3 fluid for the street since DOT4 fluid will hold more moisture. Yes, DOT4 has a higher wet boiling point but it still holds more moisture. That moisture can corrode various parts in the brake system. Given the general lack of brake fluid maintenance by the normal car owner it makes sense they would want to keep the system from having problems as long as possible. As an aside: An interesting thing is Ford DOT3 brake fluid. It is rated at a 500 degree F dry boiling point which is above what some DOT4s achieve.

Bill

Amazingly (at least for my 14) the brake fluid replacement per the service schedule is at 150K or 10 years whichever comes first.

I track my car so the DOT4 racing fluid gets bleed out a little (a caliper full?) at a time between several events. Thus after about 1 year I've completely flushed the entire system. I wouldn't let DOT4 fluid go any longer then 2 years. They make moisture testers for brake fluid - might best to just test and when its says the moisture content is too high then replace it.

I'd just go back to DOT3 if you are not tracking car because of the moisture issue. Why was DOT4 put in?

I put it in not knowing about the moisture issue. Now I know. Thanks!

I have searched but can't find any data or articles indicating DOT 4 holds more moisture. Could you share where that data is coming from?

Thanks

DOT4 absorbs moisture more quickly which is why it needs to be flushed more frequently than DOT3. This is why GM calls for DOT3 on the street but DOT4 on the track.

All 2019 Corvettes now come with DOT 4 brake fluid from the factory. Also called out in the owners manual.

?
 

You don’t consider what you are doing changing the fluid do you? The goal is to remove moisture from the fluid when you never do?

I am changing the fluid, just not all at once. This is likely not ideal for a street driven car but a common routine in tracked cars.

I guess it work for you.
 

The goal is to remove all moisture from the fluid. As you know (but others may not) under track use under extreme heat the water can turn to steam which is compressible and then you have no brakes, hello WALL.
There is moisture in your fluid. If you take some fluid out and add more there is still moisture in your fluid, a very dangerous situation. Do that for a couple years and your fluid has a lot of moisture in it.

I have a power bleeder (motive $40), I just use it to pressurize the system and keep topping it off but it is pretty easy to do by yourself. I would change the fluid once a year just to be sure, not expensive and not difficult.

DOT4 is now factory fill on 2019s

That is how I am doing it as well - push out old fluid and replace with new stuff. I normally go thru two 500ml bottles, but I am not sure if this represents the entire volume of fluid in the system.

That's what I do too. I push a half bottle per wheel,

Your changing the fluid
 

If if you are doing that you are changing the fluid. I thought you were doing one squirt per caliper.

My bad, just trying to help.

My understanding with regular DOT fluid was it should be changed out every 3 years regardless of how few miles.The reasoning was to drain the moisture in the system to prevent corrosion.This may not be the recommendation for the Corvette but it has been recommended by other cars I've owned. Has this now changed?

Seems OEMs are all over the place with their recommendations...

https://www.cars.com/articles/how-of...1420680336417/

Sort of related but what is shelf life of unopened dot 4? I have a liter that has been in the garage for a year and a half or so, I never broke the seal. Just wondering if I should use this or not.

I understand if it has been opened that you should not use it after a year or two?

DOT 4 is standard on 2019s
 

Dot 4 is standard on 2019s