GMC 2008 Chevrolet Tahoe Supplemental Owner's Manual page 46

2. Then keep turning the DMCM coolant surge tank
pressure cap slowly, and remove it.
3. Add the pre-mixed DEX-COOL™, available at your
dealer/retailer, to the DMCM coolant surge tank
until the level reaches the FULL COLD mark.
4. Turn the ignition to ON/RUN without starting the
engine. The hybrid cooling pumps will run and
any trapped air will purge to the surge tank.
5-10
5. Add the pre-mixed DEX-COOL™, available at your
dealer/retailer, until the coolant level is maintained at
the FULL COLD mark. This should take no longer
than two minutes of hybrid cooling pump operation.
If you cannot keep the level at the FULL COLD
level, your vehicle may need service. See your
dealer/retailer.
Notice: Using tap water, cooling system sealers or
conditioners in an attempt to stop coolant leaks
can damage the DMCM and engine cooling systems.
Never use tap water, cooling system sealers or
conditioners in your cooling system.
6. Then replace the
DMCM coolant surge
tank pressure cap.
Be sure the pressure
cap is hand-tight
and fully seated.