help-hot steaming green liquid 308!

This is fairly normal for 308s, although it isn't 'proper'. You should start by bleeding your system then filling the reservoir to the proper level, and see if that fixes the overflow you are seeing. You may need to replace your coolant tank's cap with a new one. My 308 would pee coolant after a drive, but after flushing, refilling, bleeding, and replacing the cap, it doesn't do that any more.

 

Its the coolant overflow from the expansion tank

If its doing it on shutdown the chances are you might be losing some coolant while you are driving as well so keep an eye on the level.

Almost certain that the root cause is a weak expansion tank cap - they just don't last - 4 or 5 years if you are lucky it seems. It is possible to test the cap - yr local autoparts dealer or local garage might be able to do it.

I.

 

Jack the rear of your car up or find a way to get the rear facing up a good gradient and let it idle and warm up. It should push the air pockets towards the expansion tank and will burp some coolant. Of course make sure the car is cooled down enough afterwards to unscrtew the cap and let any pressure off if need be. I had to do this with my mondial. Also add some redline water wetter which really helps. Also, try to get a good mixture of water to coolant of about 40/60 with the larger being coolant. You dont want too much coolant because the water actually boils sooner and acts as a kind of safety net for overheating and keeps you from doing any damage. Too much coolant and it boils at a higher temp letting you potentially damage things.