I would like someone to educate me on the purpose of the second expansion tank under the LH headlamps. My car has had a chronic leak there so I removed it and found the spigot on the side was just an open hole. I don't see any hose nearby to connect to it.
Is it there solely to collect overflow from the upper reservoir? Was the tank (MNC4460AD) originally plugged at that spigot?
Many thanks.....

 

It is suppose to be open to the atmosphere. Will leak if cracked: but if it is overflowing, most often due to wrongly connected overflow pipes from topside reservoir. The hoses need to cross over -- techs not familiar with this engine will often misroute these after radiator or water pump repair

 

The header tank is a non-pressurized "overflow" tank that enables hot coolant to be stored temporarily. When the main engine coolant is heated it expands, and if the level in the expansion tank is at the correct level this "excess" volume will overflow into the header tank, controlled by the expansion tank cap. (The header tank is designed to vent to atmosphere if the tank gets too full). When the engine coolant cools, the "excess" coolant in the header tank is sucked back via natural vacuum into the expansion tank to maintain a proper level. It is important that you do not remove the header tank.

 

The hole you are referring to was designed to be open like that. You might see some coolant leaking from the hole, but it would only be a small amount from "sloshing" during aggressive driving. The coolant level should never be high enough to run out of that hole. Normally there is only a cupful or so of coolant in that tank, most of which gets sucked back into the system as the car cools overnight. If you're seeing a leak from the open hole under normal circumstances, then you likely have a different issue as others have mentioned above. It is possible that you could have too much coolant in the overflow tank if you checked the coolant level in the regular tank before the car was overnight cold, and it had not sucked all of the coolant back in yet. If you added coolant to the system at that time, then your overflow tank might end up with too much coolant in it next time the car "burps" hot coolant, and that might be when you're seeing the fluid "leak" out the open hole. You should only check the coolant at the regular tank when the car is stone cold, usually overnight.

 

Many thanks gents, I think I see now!