Cadillac 2006 STS - Manual (Page 351)

{ 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. Do not spill coolant on a hot engine.
1. You can remove the Intercooler System pressure
cap when the Intercooler System, including the
upper intercooler hoses, are no longer hot. Turn the
pressure cap slowly counterclockwise about
one-quarter of a turn. If you hear a hiss, wait for
that to stop. This will allow any pressure still left to
be vented.
2. Then keep turning the pressure cap slowly, and
remove it.
3. Add the proper DEX-COOL ® coolant mixture to the
fill neck, until the coolant reaches the COLD FILL
line on the fill neck.
4. With the Intercooler System pressure cap off, start
the engine and let it run for a couple of minutes.
Then turn the engine off. By this time, the coolant
level inside the fill neck may be lower. If the
level drops to where coolant is no longer visible in
the horizontal tube section of the fill neck, with
the engine off add more of the DEX-COOL
® coolant
mixture to the fill neck until the level is again
visible in the horizontal tube section.
5. Then replace the pressure cap. Be sure the
pressure cap is hand-tight and fully seated.
If the coolant is not at the proper level when the
system cools down again, see your dealer.
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