Silicone Brake Fluid


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By 312YBlock - 4 Years Ago
I have had two open containers of DOT 5 on the shelf for several years, the contents look fresh. DOT 5 has been in the system since day 1. I want to flush and refill the system, do you think it’s ok to use?
By Dobie - 4 Years Ago

Unlike glycol based DOT 3,4 and 5.1 fluids, DOT 5 silicone brake fluid will not absorb water from the atmosphere or act like a paint remover. Silicone has very high dry and wet boiling points. It is also more compressible and can absorb more air than a conventional brake fluid.

DOT 5 does have its applications. If you own an extremely rare car that has expensive or original paint, DOT 5 is the fluid for you because it will not eat away the paint if spilled. But, if you use DOT 5, you are almost required to bleed the brakes before you go for a spin. Why? DOT 5 is lighter than water. Any moisture will pool at the lowest point which is typically the calipers or wheel cylinders. Many classic cars have been lost after the owner decided to shake loose the cobwebs before bleeding the brakes.

If you have been using it since replacing your brake lines/hoses and calipers/wheel cylinders you should be good to go. If you've been using regular fluid you will need to replace those components as the two type of fluids don't play well together.
By 312YBlock - 4 Years Ago
Thanks for the info. I’ve used DOT 5 since day 1 which was in 1985, never had a problem 😊
By paul2748 - 4 Years Ago
Every time you go for a spin - that's laughable.  I've had dot 5 in two cars for years and never had a problem
By KULTULZ - 4 Years Ago
Every time you go for a spin - that's laughable.  I've had dot 5 in two cars for years and never had a problem.


What was posted regarding DOT 5 is true and not laughable. You need to research the subject before posting such a reply.
If one decides to use DOT 5, the only way to know if damage has occurred is to remove and inspect components, or a possible failure as mentioned.
By Lord Gaga - 4 Years Ago
I believe he's asking about shelf life.
By 312YBlock - 4 Years Ago
Yes that’s all I’m asking 😊
By KULTULZ - 4 Years Ago
If it were me ...

Seeing as how the containers were not sealed and even though DOT 5 is not hygroscopic, I would pour the contents into a clear glass beaker and let it sit (covered) for awhile to see if any water vapor (atmospheric) has compromised the fluid. There will be water separation collected on the bottom of the container.

Research DOT 5.1
By KULTULZ - 4 Years Ago
BTW -

Plastic containers are permeable, atmospheric water vapor being able to penetrate the container(s) over time. It is also true with motor oil and ATF. That is one reason for DATE CODING, especially with modern automatic transmissions..
By Ted - 4 Years Ago
The best information I find is that Dot 5 brake fluid can be stored indefinitely as long as it’s in a closed container.  This is due to Dot 5 brake fluids’ inability to absorb moisture.  On the other end of the scale are the glycol based brake fluids which some manufacturers recommend discarding after one year of opening.  Sounds pretty extreme on that but I can see where the manufacturers are covering their tails for litigation purposes.

The same old arguments tend to surface each time the use of Dot 5 brake fluid comes up.

I have been using Dot 5 fluid for over forty years and normal maintenance is the rule.  I also tag the master cylinder covers for those vehicles with “Use Dot 5 Fluid Only” labels.  Dot 5 fluid cannot be mixed with other types of fluid and subsequently, the systems must be completely purged and cleaned of any residual non-Dot 5 fluid when switching over to Dot 5 fluid.

In my opinion, the pooling of moisture within the system is exaggerated and goes back to military applications where brake systems were exposed to extreme amounts of water.  If you are an off roader and like to traverse creeks and streams, then Dot 5 brake fluid is probably not the best choice for that.  There are issues with anti-lock brake systems and aggressive braking that do come to the forefront but that’s another subject.  For those of us with collector cars, those are not issues.  In having to go back into brake systems that use Dot 5 fluid, I’ve found those systems very clean and rebuildable as compared to the systems that use Dot 3 & Dot 4 brake fluid.  Just my two cents worth on the subject.
By 312YBlock - 4 Years Ago
Thanks Ted for the input and to all 🚙