I'm presuming your daughter's Camaro is 1996 or newer, meaning it's
equipped with Dexcool. I've seen this several times on Dexcool vehicles.
The only thing I've ever been able to do is flush it out with a garden
hose. Pull the thermostat out. Pull the heater hoses off the engine.
Pull the lower hose off the radiator.
Run the water each direction through the heater core. Run the water into
the upper radiator hose at the thermostat housing (presuming that's where
the hose attaches), through the radiator and out the bottom. Run the
water into the engine through the thermostat housing until nothing but
clean water comes out the lower radiator hose.
When you're done with this, I'd recommend installing regular green coolant
and then changing it every one or two years. Use your judgment regarding
replacing the thermostat.
Be aware that you may need to do this again. Without fail, you won't get
everything. Also, it's possible that the radiator and/or heater core is
already clogged to the point it won't clear out.
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