Disappearing Brake Fluid
 

Got a weird thing going on, ever since it became an Arizona car the brake fluid has been disappearing. Half of the time after sitting for more than a couple weeks on the first start up the "brake fluid low" warning comes on and it needs to be topped up. I'm not just trusting the light, it is actually low and its blows me away where it could be going. Tonight after sitting less than a month the brake fluid was extremely low, the E-brake light and the traction control disabled light were all on on start-up.

It gets pretty hot in the garage sometimes, 110+ F sometimes, could it be evaporating or do I maybe have some kind of internal leak? There is no sign of leakage on the floor or at the brakes themselves.

I did some searching online and any case of disappearing fluid I could find was on much older cars and pointed to a bad master cylinder or fluid leaking out of the filler cap which there is no sign of. Any insight would be appreciated.

If there are no external leaks evident, it could be going out of the back of the master cylinder in to the vacuum brake booster. It would be strange for this to be happening on such a "young" car, but if you're losing fluid, and can't see it anywhere else, that may be the answer. Pull the large hose connection going to the booster, looks for signs of fluid in the booster.

cheers
Ed

Thanks Ed I'll check it out. The car is very young, just rolled past 30,000km in 6 years.

Might not hurt to try a new cap anyway, and maybe get a brake inspection. If something bizarre is happening like multiple calipers leaking, maybe it's not leaving evidence on the floor but leaking enough to be low.

I'll pick up a new cap. It was in for oil, filter and inspection in February and everything checked out ok but I'm sure it wouldn't hurt to do it again.

Unless it was requested they probably didn't pull the wheels to check the brakes, a quick peek through the wheels might not allow them to see close enough.