1999 XJR
Coolant started flowing out from front driver section. After cooled down, refilled 50/50 and turned the car back on waited. After 4-5 mins the coolant fluid was gushing out of spout, mid-way down the side of the 'overflow tank', spout faces the windshield. Looked underneath and did not see any loose/hanging hose anywhere. Upon searches, I see a lot of discussions about the reservoir tanks but not on the overflow tank. Question is the spout supposed to attached to a hose or does it have a plug that must have deteriorated and broken off? HELP!

 

First, welcome to the forum. If you haven't done so yet please go to the new member section and introduce yourself. Tell us a little about you and your vehicle. We are a friendly group and want to get to know you. Second, just for the record on future posts the appropriate section for posting your questions is the X308 forum. So now to get down to business addressing your question. Attached you will find a parts diagram for the cooling reservoir and overflow tank. There is no connection to the overflow vent that you are describing. It is open to the atmosphere.
The problem appears that after a short time at temperature the overflow tank is filling to fast, correct? If that is correct there are two reasons for it. First is the Expansion tank cap has gone bad and is relieving at low pressure. The second is a little trickier to diagnose without seeing a picture of the hoses connected to the expansion tank. It is a common error to connect the hoses incorrectly to the expansion tank and cause overflow problems.
When viewing the parts lay out hose #7 runs from the front of the engine and connects to the nipple closest to the fender. Hose #4 runs from the overflow tank and connects to the nipple furthest from the fender. The appearance is that they cross over each other. That is the correct installation, if they are connected side by side and not crossing then they are connected wrong.

Take a look at your hose installation and if it is correct I would recommend a new cap for the expansion tank.

 

Sorry for late reply but have been traveling on business!
First of all, apologies as I thought I had correctly posted the question but I assume when I was searching I bounced over to other sections.
Just before you replied I found a few threads that spoke of the potential issue with the incorrectly connected hoses. And then after your post, I decided to make the switch. I instantly became Charlie Brown yelling "That's it!".
Bless you and this forum as it brings back a level of hands-on pride of accomplishment that I can still fix a car whereas my Odessy and Rav4 are impossible to access and have fun with. My next journey will be restoring the body.

 

Congrats, on solving your problem. There are many folks here always willing to help.