Can I top off my brake fluid with synthetic? It is a bit low.

And then just keep replacing it with synthetic as it runs low?

I have regular brake fluid now.


thanks in advance

i think the only fluids you can top off in a car are windshield washer fluid, and gas.

everything else you should drain and/or flush and refill.

and no, don't mix and match.

Our standard brake fluid is a DOT 3 (correct me if I'm wrong), and you gotta flush it all if you're going to change the type. My xb uses a DOT 5 silicon based fluid, but I have upgraded lines and such (plus I drive like the devil).

Brake fluid is something that you usually don't top off between brake jobs. When your brake fluid drops to a certain level the red brake light will come on on your dash letting you know that your brakes are getting low. After you do whatever repairs are needed then you top it off if needed.

You can mix synthetic and standard brake fluid of the same type (dot-3, dot-4, etc) as long as the car doesn't specifically require synthetic (ours doesn't).

You can use dot-4 in a car that calls for dot-3 with no problems. But you should never put dot-3 in a car that calls for dot-4 (boiling point is too low).

Dot-5 is silicon based and is not compatible with any other brake fluid.

If i remember correctly there is a dot-5.1 brake fluid that is backwards compatible with dot-3 and dot-4 though I have never saw it in person.

BAD IDEA, I have heard that if you put synthetic in it, you will be replaceing all of the rubber very soon in your entire system, and who knows what it will do to the ABS unit.

I haven't seen it but this was coming from a Jaguar Tech of 25 years, this is when I was a Lotus Tech, but you don't want to find out!! :nails:

dont top off your fluid!!!! as soon as you change your pads
it will spew everywhere.. don't mix it either.. I did a full Motul
RBF600 swap, and it was easy..
I get cars for brakes all the time, and when they go to jiffy lube for an oil change they "top off" the fluid, so when I push
the piston back in.. well, now I gotta clean the floor.. I think
its a stupid practice (no offense to you, I just have to deal with it all the time, and people think its the right thing to do,
the level tells you where your pads are or if you have a leak, if you have a leak your pedal will drop to the floor. If that ain't the case, leave it alone).

BAD IDEA, I have heard that if you put synthetic in it, you will be replaceing all of the rubber very soon in your entire system, and who knows what it will do to the ABS unit.

I haven't seen it but this was coming from a Jaguar Tech of 25 years, this is when I was a Lotus Tech, but you don't want to find out!! :nails:
it won't do any of that, as long as it has the same DOT rating, it acts the same. Synthetic reacts better to temps. Lasts a little longer..

BAD IDEA, I have heard that if you put synthetic in it, you will be replaceing all of the rubber very soon in your entire system, and who knows what it will do to the ABS unit.

I haven't seen it but this was coming from a Jaguar Tech of 25 years, this is when I was a Lotus Tech, but you don't want to find out!! :nails:
it won't do any of that, as long as it has the same DOT rating, it acts the same. Synthetic reacts better to temps. Lasts a little longer..

Thats the thing DOT 5 is synthetic and DOT 3 and 4 are not. I am sure it lasts a little longer but thats only if your system came with it from the factory!

And topping off is not a bad thing, you should NEVER push the fluid back it to the system, if your fluid gets dirty, which it does, it has the possibility to clog your ABS Unit, if you can bleed the system as you are changing your brakes, all of the clean fluid will be better.

BAD IDEA, I have heard that if you put synthetic in it, you will be replaceing all of the rubber very soon in your entire system, and who knows what it will do to the ABS unit.

I haven't seen it but this was coming from a Jaguar Tech of 25 years, this is when I was a Lotus Tech, but you don't want to find out!! :nails:
it won't do any of that, as long as it has the same DOT rating, it acts the same. Synthetic reacts better to temps. Lasts a little longer..

Thats the thing DOT 5 is synthetic and DOT 3 and 4 are not. I am sure it lasts a little longer but thats only if your system came with it from the factory!

And topping off is not a bad thing, you should NEVER push the fluid back it to the system, if your fluid gets dirty, which it does, it has the possibility to clog your ABS Unit, if you can bleed the system as you are changing your brakes, all of the clean fluid will be better.

Motul RBF600 is synthetic DOT3/4 compliant
Fluid doesnt get dirty, it gets affected by moisture, and turns to green sludge
You should NEVER bleed the brakes just because you are changing pads
The fluid does get pushed back in for brake jobs, thats why there are piston return tools that provide a lot of force
I'm a 10 year tech, current certified Acura master tech, and would not spread anything untruthfull.
All of this is easily verified via an internet search as well.
Clean fluid is better, and most manufacturers reccomend a flush every 30k miles, but most go longer. I do it as soon as its starts getting dark, but i'm in a shop all day and its easy for me to knock out.

I will give you that it is a common reccomendation not to
push fluid back through the master cylinder, However theres
two reasons why I would never reccomend the average joe
to do it. First being that I have never seen this cause an
issue on any car, and I doubt anyone who takes their car to
a shop for pads, see's fluid on the reciept. It just isn't done
anymore. The second is that I get a car on a flatbed at least
once a month with a spongy brake pedal or no brake pedal feel after someone attempted to bleed their brakes while doing pads. Most don't have the know how or equipment to
do this correctly. I just dont see telling anyone they should never push the fluid back in, when theres more to lose than gain.

tech at REDLINE advised the ATE' brake fluid few days ago on phone . GOOD LUCK

Street, I see what you are saying, I guess I forget a few times that there are average joes out there, I guess it is a little different if you are a tech. I guess, personally, I don't like pushing the fluid back into the system.

But if you have Motul fluid, I would not just use that to top off my fluid, thats when I would do a complete flush.