The white smoke (or steam) from coolant can enter the cockpit.
It also depends where the plane is hit. A hit in the radiator, behind and below the cockpit, will trail steam, but most likely not enter the cockpit.
A hit in a coolant line under the cockpit or in the engine bay, may allow smoke into the cockpit. It all depends where the hit took place.
http://usautoindustryworldwartwo.com...-51-107w-2.jpg
http://www.enginehistory.org/Allison...ysteminp51.jpg