This is a coolant reservoir containing Dexcool. Dexcool is orange. If the coolant is dark orange or rust, it needs
to be replaced. A dark rust color indicates that the coolant has lost its ability to protect against rust, and
oxidation and rust have taken over. This happens when the coolant loses its ability to lubricate and protect the
cooling system. This color indicates that the system is now internally rusty and scale buildup is accelerating.
The system should be tested for integrity, then flushed and filled with a fresh 50-50 mix of coolant. I
recommend replacing the thermostat as well because the system probably overheated.
Consistency
The engine coolant should feel slippery to the touch and smooth (like the engine
oil). If it feels gritty, the coolant is dirty and should be flushed and replaced with
a fresh 50-50 mix. If it’s lost its lubricity (not slippery), then the lubricating and
rust inhibitor agents are gone and the system is at risk for rust and scale buildup
as well as water pump wear.
Smell
Change the coolant if it smells burnt. Also change the thermostat; it’s probably
gone bad because it was exposed to overheating (or it caused the overheating).
Overheating damages the bi-metallic spring that opens and closes the thermostat
valve. Most important, find out what caused the system to overheat and repair it,
or face major engine damage.