Chevrolet TRACKER 2003 Manual page 245

If the overheat warning continues, there's one more
thing you can try. You can add the proper coolant
mixture directly to the radiator, but be sure the cooling
system is cool before you do it.
Steam and sca._..ng liquids from a h co ng
system can blow out and burn you badly. They
are under pressure, and if you turn the radiator
pressure cap
--
even a little
--
they can come
out at high speed. Never turn the cap when the
cooling system, including the radiator pressure
cap, is hot. Wait for the cooling system and
radiator pressure cap to cool if you ever have
to turn the pressure cap.
5-36