can i mix brake fluid DOT4 with DOT3?

i mix until dunno what colour
techincally can use
but my forman said will damage ur porpotion valve and pump/servo at ur brake system in long run

owh.that means not recommended to mix la.thanx

is not recommend to mix. I did mix before in my sunny last time. At the end,,master pump died, inside rubber spoilt.

cannot mix laa.... flush out everything and pour in fresh one...

YES. Anyone who tells you that you can't mix it or it will damage something has no idea what he's talking about.

DOT 3, 4 and 5.1 are all fully compatible with each other. DOT 5 fluids are the odd ones out, but you won't commonly see them unless you're riding a Harley or so.

don't believe is up to u. I already tried and it spoilt the rubber inside the master pump.

Dot 3 red fluid + Dot 4 very light yellow fluid = my master pump rubber KO

why would you want to mix?

yesterday i buy brake fluid at spare part shop.i ask for myvi and he said myvi use dot4.later when i go back home n want to topup the fluid i saw "use DOT3 only" on my brake fluid cap.tat why la i ask

DOT3 is the minimum standard for the brake fluid you can use in your car. DOT3, 4 and 5.1 are all glycol based fluids and can be freely mixed, with the caveat that if you mix expensive DOT5.1 fluid with DOT3 you can't expect the fluid to boil at DOT5.1 temperatures (to put it in the form of a computer analogy - if you have a PC using DDR3-800 RAM and you put in a stick of DDR3-1066 you can't expect the old RAM to run at the higher speed)..

The colour of the fluid doesn't really matter; most brake fluids are almost colourless or they might have a slight yellow tinge. Manufacturers sometimes add dyes to the fluid so that its easier to see.

May I ask why you're topping up your fluid though? That should be one thing you don't need to top up unless you have a leak! As your pads/shoes wear it is normal for the fluid level to drop (the pistons in the calipers/drums keep moving towards the rotor/drum hat to take up the wear). If your fluid is near the minimum level, it's quite likely that you need to change your pads. When you do change your pads, a fluid change isn't a bad idea.

when i check,my fluid level near the minimum.so i need to change my brake pad and after tat topup the fluid?

Sorry, saw your PM before this reply.

Check your pads, change them if they're worn (they probably are) and have the fluid changed. Brake fluid *must* be changed at least once every two years as the glycol base in it absorbs water. Brake fluid which has absorbed water will have a reduced boiling point, which you will find out very quickly if you use your brakes very heavily - think of going down Genting.

its ok.later i'll check my brake pads.

That's just because your master pump is about to go. It's just like mixing fuel RON 95 + RON 97 + V-Power. The brake fluids are all the same and they are non-corrosive (except for Dot 5.0) and will never 'makan' your master pump seal. The Dot 3/4/5.1 are just ratings/specifications that determine the boiling point of the fluid, etc, etc, etc.

Do you know what DOT means? Department of Transport and I'm not kidding you. Used in the US and adopted worldwide.

DOT = Department of transportation? Really?

i don't know.