Brake fluid Consumption

I think the brake pads wear down.

 

Unusual, no doubt.
I don't think the brake fluid level has changed in 10 years in our '04 Prius.

I suggest first convincing yourself that the reservoir cap is on snug; and if that is not it then time for you or a mechanic to find the leak.

 

As the pads wear the fluid goes down to fill the calipers. Fluid going down a little is normal... going down a lot is not. If you think its abnormal drop first check all your calipers for obvious leaks. Take off the front wheels and do a visual inspection. No leaks should be visible. I think what you are experiencing is normal pad wear and the regular fluid drop. Do a visual inspection to be sure. Prius have great pad wear because of the regen braking. On my 2nd gen I have almost 126,000 mile on my original pads. they still have about 1/2 their life left!
-Paul R. Haller-

 

The dropping of the brake fluid doesn't have anything to do with the brake chatter over bumps. That's just too much play with the pads bouncing up and down. Was the fluid down to the seam near the bottom of the reservoir?

 

I already called the dealer and will be taking it there tuesday. The car is still under warranty, now i wonder if i should purchase an extended warranty


Good, go to dealer, prii don't really use brake pads, and dropping fluid is a leak, usually involving air in the system and a spongy brake pedal.
There's no question when it involves brakes, go to a competent mechanic, and hopefully the dealer is.

Read the extended warranty, save your money, this would be the first leaking brake syndrome yet, very unusual.

 

Ok, since the car is still covered, bringing it back is the best bet.

 

Now I'm beginning to wonder how much the level changed -- say, in mm ?

 

3 fingers drop is a lot. A leak seems quite likely.

Good Luck !

 

In a "conventional" system with a vacuum brake booster, brake fluid loss without evidence of an external leak usually means that the fluid is entering the booster. For a Prius, with its nitrogen-charged bellows accumulator, could the OP's observation mean that fluid is entering the bellows?

 

Brake fluid shouldn't be "consumed". The system should be tight, if the level is dropping excessively, it's leaking, somewhere.

Note the emphasis on "excessively": as brake pads wear, the break fluid level in the reservoir will go down. In my experience with past cars, when the level reached the lower mark the pads were reaching their minimum thickness.

If that's the situation it's simpler to not add fluid: you'll only need to baste it it out of the reservoir when you push back the pistons to accept new pads, or it will overflow.

But in your situation: if there's little pad wear while the level is dropping quickly, something's amiss.

 

I had a similar situation with my car. I am 99% sure the brake fluid level was at the full mark on mine since new. One day I noticed it was about 3 fingers low as the OP reports. I took it to the dealer and they topped it off to the middle mark and looked for evidence of a leak but could not find one and asked me to continue watching for signs of a leak. I watched for a while and have never found any signs.

I checked my brake pads and there are no signs of brake pad wear. IIRC the new pads are 11 mm and mine were at 9 mm after 30k miles.

The low mark on the brake fluid reservoir is actually well below the middle level mark. I took a sharpie and marked all of the level marks on all of my reservoirs for easy reference.

I have not had any further issues with my brake fluid level since.

 

Check the ground where you frequently park the car. If there's nothing there, and nothing showing on the engine compartment plastic underpanels, it could be there's nothing wrong. The level could be going up/down due to mysterious ways of the computer control and the various components. I'm not saying you're dreaming, just that there could be an explanation that doesn't involve a problem with the system. Do keep an eye on it.

 

Since the normal compression of the accumulator bellows could change the reservoir level, I suggest that you always check the fluid when in READY mode -- when the accumulator is charged.

 

If the accumulator was leaking internally I would imagine the system would be doing some really weird stuff. Also, It could only leak so much as it would eventually be filled.

Avi