Brake Fluid... DOt 3 or 4...

[MatthewDavid]

I read that 97' my mark viii takes dot 3 brake fluid... but I read somewhere that dot 4 is pretty much the same thing sept some esters... I'm just asking cause my friend has a lot of dot 4 in his shop and we're gonna bleed the brakes... I was wondering will it hurt if I use dot 4?

 

[MatthewDavid]

So nobody answered it so read a bit and called around... just in case anyone else wants to know sometime... they're pretty much the same thing... Dot 4 is a newer version of dot 3 that has a higher boiling point... you have to be careful that it won't eat out your silicone parts though... but most cars are compatible of using either one

 

[JMiles_T]

If you can get it for the same price as the DOT 3, I don't see why not.

I have yet to read about any problems with it from other people on this or the other message boards for our cars.

I've been using Valvoline SynPower fluid for years with no trouble.

 

[Frat-man-du]

When I replaced 100% of my 65's brake system I switched to DOT 5 Silicone fluid - great stuff does not absorb water like DOT 3/4 and wont hurt paint if it gets dripped on it. Strange looking purple fluid and had to be heated up to remove air out of the fluid before using but I have had in for years now and works great.

 

[JMiles_T]

You shouldn't use silicone based DOT 5 fluid in cars with ABS systems.
The pump cycling can cause cavitation.

There's glycol based DOT 5 fluid out there that may be okay.

 

[Dawkins]

So really the question is if your adding calipers all the way around...and u bleed the system dry...could u really use dot 5...even though its $12.49 for 350ml compared to dot 3's $4.49 for 350ml..."Dot 5 silicon brake fluid exceeds the performance of dot3 and dot 4 fluids. offers reduced corrosion, no loss of boiling point. Wet boiling point min. 180C or 356F"..."IMPORTANT: Only add dot 5 silicone brake fluid to the system when it is completely free of dot 3 or dot 4 fluids. Never mix fot 3 or dot 4 fluid anywhere in the braking system"...so question is has anyone done it and had any problems per say...been told the master cylinder might no be able to hold dot 5 due to the seals in the cylinder....??

 

[unity]

Actually DOT 5 will SAVE the brake system, it wont hurts any seals at all and in fact will very much pro-long the life.

But as mentioned you can not mix them at ALL. When, well if ever, I get a new brake system I will replace ALL lines, ABS pump, etc and use DOT 5.

My friend, who restores a great many vintage vehicles, always used DOT 5.