GMC T-Series 1999 Owner's Manual page 220

Adding Coolant
If you need more coolant, add the proper DEX
coolant mixture at the coolant recovery tank or the
surge tank.
CAUTION:
Turning the radiator pressure cap (on a gasoline
engine) or the surge tank cap (on a diesel engine)
when the engine and radiator are hot can allow
steam and scalding liquids to blow out and burn
you badly. With the coolant recovery system, you
will almost never have to add coolant at the
radiator. Never turn the radiator pressure cap
or the surge tank pressure cap
--
little when the engine and radiator are hot.
Add coolant mixture at the recovery tank or the surge
tank, but be careful not to spill it.
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COOL
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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.
Some conditions, such as trapped air in the cooling
system, can affect the coolant level in the radiator. If you
need to add coolant to the radiator, follow the steps
listed under "How to Add Coolant to the Radiator."
See "Engine Overheating" in the Index.
Engine Coolant (Caterpillar
Diesel Engine)
If your vehicle has a Caterpillar diesel engine, see the
R
Caterpillar Operation & Maintenance Manual provided
with your vehicle to find out what to add, also when and
how to service your cooling system.
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