GMC 2000 Sierra - Manual (Page 334)

yellow blue
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Adding Coolant
If you need more coolant, add the proper DEX - COOL
R
coolant mixture at the surge tank, but only when the
engine is cool.
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 replacing the pressure cap, make sure it is
hand
- tight.
Coolant Surge Tank Pressure Cap
The coolant surge tank pressure cap must be fully
installed on the coolant surge tank.