It should be up to the cold mark ( at least that's the way it is on my vehicle )
Look on the side of the coolant overflow bottle. There should be a low mark for the coolant for a cool engine, and one for a hot engine.
You should add coolant with the engine off and cool, top off the radiator and fill the coolant reservoir to the cool or cold level. When the system is hot or running it will be pressurized and will be dangerous to open. You can however add coolant to the overflow reservoir at any time.
Remove the radiator cap when the engine is cool and add the coolant into the radiator or you can add to the coolant overflow bottle. DON'T remove the radiator cap when the engine is hot!!!
In the coolant reservoir when the engine is cool.
The coolant expands when heated, contracts when cool. The coolant reservoir gives the coolant a place to come and go as needed.
Coolant only moves from the overflow tank/container to the radiator when the engine is cooling. It flows the other way (into the tank) as the engine heats up and coolant expands. If coolant isn't moving into the radiator when the engine is cooling down there could be a couple of reasons. 1. The engine really never got warm enough to begin pushing coolant to the tank and the radiator is already full. 2. The radiator cap is faulty and should be changed. 3. If the coolant hasn't been changed for many years it's possible (though unlikely the hose linking the tank and radiator is plugged. Thoughts: Be sure you're adding a 50/50 mix of coolant and distilled water to the overflow tank, not just water. Note the coolant level in the tank with the engine cold then go for a drive. Check the level again. It should be a little higher. Let the engine cool and the level should be back to the original point. If that's the case you're good to go. If coolant is pushed into the overflow but the level doesn't drop again blame the radiator cap and get a new one. Cheers
The overflow bottle may overflow if: 1. The car is overheating - this means after the coolant in the radiator gets heated up and expands it flows to the reserve bottle but the radiator doesn't cool down to suck back the coolant from the overflow bottle, but just keeps on sending coolant to the bottle. 2. You may have put excess coolant in the bottle - hence heated coolant from the radiator didn't get enough space.
If you are getting exhaust smoke coming out of the radiator overflow, you need to replace the head gasket that seals the cylinder from the cylinder cap where your coolant runs through to cool the engine.
dex-cool coolant---it is orange in color.
Check the coolant level in the overflow bottle. It is a clear(ish) plastic bottle with a flat, black cap on it. There should be a hose going into it that starts at just below the radiator cap. There should be two lines on the bottle, one marking the full level when the coolant is hot, and a lower one that marks the full level when the coolant is cold.Check the level with the engine off.If you need to add coolant, pour fresh coolant into the overflow bottle, NOT the radiator itself. You should use a 50/50 mix of Dex-Cool extended life coolant and clean water. Using the green, ethylene glycol coolant can cause damage to your cooling system.After you add, drive around for awhile until the engine has reached operating temperature, then shut the engine off and check the level again. Top off if needed.
When the engine is cool
The engine needs to be flushed.the coolant ports have a build up of gunk causing the engine to run hotter. The heated water expands to much causing it to over flow from the reserve tank.