Chevrolet 2000 Tahoe Owner's Manual page 327

Brakes
Brake Fluid
There are only two reasons why the brake fluid level
in the reservoir might go down. The first is that the
brake fluid goes down to an acceptable level during
normal brake lining wear. When new linings are put in,
the fluid level goes back up. The other reason is that
fluid is leaking out of the brake system. If it is, you
should have your brake system fixed, since a leak
means that sooner or later your brakes won't work well,
or won't work at all.
6-28
Your brake master cylinder
reservoir is filled with
-
DOT 3 brake fluid.
So, it isn't a good idea to "top off" your brake fluid.
Adding brake fluid won't correct a leak. If you add fluid
when your linings are worn, then you'll have too much
fluid when you get new brake linings. You should add
(or remove) brake fluid, as necessary, only when work is
done on the brake hydraulic system.
CAUTION:
If you have too much brake fluid, it can spill
on the engine. The fluid will burn if the engine
is hot enough. You or others could be burned,
and your vehicle could be damaged. Add brake
fluid only when work is done on the brake
hydraulic system.
Refer to the Maintenance Schedule to determine when
to check your brake fluid. See "Periodic Maintenance
Inspections" in the Index.