I'll take a pic and show u

 

 

If that line is missing, it could be the reason you are losing coolant.

 

under this cap is the dipstick for the coolant level

 

Do you have a small hose going from the radiator to the overflow container?

 

on the radiator itself, there is a small hose coming off the neck right below the radiator cap

 

That hose should be going to the overflow container. Do not completely fill up the container because it will overflow when the engine is hot. The way the system works:
The radiator itself should always be full to the bottom of the radiator neck. The overflow container should be about 1/3 full when the engine is cold. There should be a flexible plastic dipstick attached to the bottle cover. When the engine gets hot the coolant expands and the radiator cap allows it to flow to the container. When the engine cools down the radiator cap allows the coolant to flow back into the radiator so that it is always full. If you overfill the overflow tank, when the engine gets hot the overflow tank will actually overflow and dump the coolant out. There is also the possibility that the radiator cap is the wrong type or not working properly, so that it only allows coolant to flow out of the radiator but does not allow it to flow back in.

 

hmmm, I've never seen or noticed a vent hole like that on my overflow cap.

If coolant is being forced up and out that hole, I would think the system may be clogged somewhere to where the back pressure is forcing it out if there is an actual problem. Also like Pete says, you should fill the coolant in the radiator not the overflow first. Put coolant in the radiator until it gets close to where that overflow hose runs out. Run the engine for a short while and then check it when it cools again. If it's dropped then fill it back toward the top again. Then you can go into the overflow and check the level there. The dipstick has indicators of where the coolant should be when hot/cold. Just fill accordingly. You shouldn't be refilling your coolant directly at the overflow.

 

Im going to flush the radiator today, I noticed debri under the radiator cap. I was thinking a possible clog as well. I haven't flushed the radiator since I got the car. Been about 2 yrs. This problem having to add coolant has been going on for almost a year but the smell just started about two months ago

 

I had a coolant leak on my RS and smelled coolant -- was the timing cover gasket -- now fixed.

You should get some super flush and clean out your cooling system - do it a 2nd time if its really gunky... Should probably replace your thermostat while you're at it... You should be ideally flushing your coolant every season if using the green coolant and less frequently if using the GM spec'd DEXCOOL orange coolant (see Owner's Manual)...