GSteg

iTrader: (15)

The chemistry may still vary to achieve the boiling point rating. Hygroscopy level between the same brand for DOT 3 and DOT 4 may not be the same, even though it may not matter much in a daily driven car. Rarely do I mix the two since brake fluids are cheap anyways.

mitsuguy

iTrader: (2)

no, you are right, you should never mix, as there is always the possibility of a chemical incompatibility... but, not to a point where the cars specifications will change due to it... if a car can handle DOT3, it can handle DOT4... per DOT regulations, the number only specifies minimum dry and wet boiling points, and all DOT 3,4,5.1 fluids are glycol based...

radicalrev

iTrader: (2)

Do any1 here use DOT 4 on their DOT 3 brakes?? Or vice versa?

jeff1941

Just recently did a brake job so i did brake flush. car uses dot 3, label of cap says dot3 only but i put in dot4 and it so far runs fine.

radicalrev

iTrader: (2)

So i guess it is okay huh? i should call up lexus and ask

mitsuguy

iTrader: (2)

the only answer you will get goes something like this: "use lexus approved fluids or fluids that meet lexus design specifications"

and yes, it's ok... unless the manufacturer specifically says it is not incompatible, then it is compatible, so long as you are replacing all of the fluid...

again, the ONLY difference between DOT3 and DOT4 is dry and wet boiling points from a regulatory perspective... from a manufacturing perspective, it means they must use a glycol based fluid, but the composition of that fluid is going to be different from manufacturer to manufacturer, and will also be different depending on how good that manufacturer wants the fluid to work...

don't mix and match fluids and you are fine (stay away from DOT5, it is not compatible - it is silicone based and was a bad idea to start with IMO)

radicalrev

iTrader: (2)

thanks for all of the answers!!