Buick 1999 Riviera Owner's Manual page 216

CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol
and it will burn if the engine parts are hot
enough. Don't spill coolant on a hot engine.
When the coolant in the coolant recovery tank is at
FULL COLD, start your vehicle.
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.
5-14
CAUTION:
Steam and scalding liquids from a hot cooling
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.
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