What type of brake fluid do you use, DOT 3,4 or 5?

[Back N Black]

Just looking for the best option, since my brake system is new from front to back. I was leaning toward the DOT 5, silicone base. Opinions please.

Thanks

[y3chargerrt]

I use dot 5. Main reason being it won't strip paint.

[69ISFINALLYMINE]

I think it is also better with preventing moisture in the brake system and doesn't boil at elevated temps?

Dot 3 minimum, but Dot 5 if you can get it easitly (it is readily available, but not all stores carry it).

Doc
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I use dot 5. Main reason being it won't strip paint.

[4aThrill]

they also have DOT 5.1 too  it can be mixed with DOT 3 or 4 here is a website with more info http://www.synlube.com/brake.htm also it's a non- silicone base aswell.  I have been doing alot of research in this area aswell 

[Back N Black]

they also have DOT 5.1 too  it can be mixed with DOT 3 or 4 here is a website with more info http://www.synlube.com/brake.htm also it's a non- silicone base aswell.  I have been doing alot of research in this area aswell 

That's a good read, thanks for the link. 

[Chatt69chgr]

It looks to me like the DOT 5 Silicone would be the best choice in a brake system that is completely new.  Regular brake fluids are hygroscopic and absorb water.  The water in the brake fluid is what causes iron and steel surfaces to rust and form the brown sludge you find in wheel cylinders.  And I think the DOT 5 has a higher boiling point than the regular type brake fluid.  It doesn't mix with reqular brake fluid so if you had a system that had that in it, you might not be able to get it all out so might not want to convert to DOT 5.  But if you were restoring your car and were to  install new master, calipers, and wheel cylinders, you could blow what is in the lines out with compressed air and probably run some of the Dot 5 through them to clean them out and then successfully iinstall the DOT 5.  I didn't realize that the DOT 5 wouldn't dissolve paint but this seems to me to be a extra plus.  I am assuming that the rubber used in master cylinders, brake calipers, and wheel cylinders and proportioning valves is compatible with the DOT 5.  Comments? 

[Charger-Bodie]

It looks to me like the DOT 5 Silicone would be the best choice in a brake system that is completely new.  Regular brake fluids are hygroscopic and absorb water.  The water in the brake fluid is what causes iron and steel surfaces to rust and form the brown sludge you find in wheel cylinders.  And I think the DOT 5 has a higher boiling point than the regular type brake fluid.  It doesn't mix with reqular brake fluid so if you had a system that had that in it, you might not be able to get it all out so might not want to convert to DOT 5.  But if you were restoring your car and were to  install new master, calipers, and wheel cylinders, you could blow what is in the lines out with compressed air and probably run some of the Dot 5 through them to clean them out and then successfully iinstall the DOT 5.  I didn't realize that the DOT 5 wouldn't dissolve paint but this seems to me to be a extra plus.  I am assuming that the rubber used in master cylinders, brake calipers, and wheel cylinders and proportioning valves is compatible with the DOT 5.  Comments? 

tHats all we use is DOT 5 in all new systems, never had anything but good results.

[Big_John]

OK.. a couple comments from the new guy...

Silicone fluid is OK to a point. Silicone has a couple issues that may not make it the ideal product. Number one is silicone doesn't asborb water like Glycol based fluids. Any moisture in the system will go to the lowest point and sit there, where  glycol will hold the water in suspension.

Silicone and glycol are also not compatible, so you really need to start from scratch with new components as you'll never really get the old fluid out. Any sludge left behind will tend to cause some problems, although that mostly hurts later cars with ABS. 

DOT 5 does have a higher boiling point spec at 500* while DOT 3 is 401* and DOT 4 is 446 but its common for the synthetic DOT 3/4 fluids to have an even higher boiling point. For example the Ford DOT 3 Heavy Duty specs at 550*

That's not to say its not good stuff, its great for a show car, but there are some limitations.  Here's some good reading on the subject:

http://www.xs11.com/tips/maintenance/maint1.shtml

Myself, I use Valvoline DOT3/4 Synthetic. When I was autocrossing, I needed a high boiling point brake fluid for the cars. Valvoline was rated pretty high, was affordable and I could get it at the local parts store. I used to change the fluid once every season.