1998 GMC Suburban Owner's Manual - Page 324

Brakes Brake Fluid Your brake master cylinder reservoir is here. It 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. I I If you have too much brake fluid, it can spill on the engine. The fluid willburn if the engine is hot enough. You or others could be burned, and your vehiclecould be damaged. Add brake fluid only when work is done on the brake hydraulic system. There are onlytwo 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, sincea leak means that sooneror later your brakes won't work well, or won't work at all. Refer to the Maintenance Schedule to determine when to check your brake fluid. See "Periodic Maintenance Inspections" i n the Index. 6-32