Ok on my 90 4.0 I converted it to an open style using a filler neck and 1 qt overflow bottle which I was told is plenty big. I guess the bottle is just defective but I wanted to ensure I did not do something wrong or choose a wrong bottle.

The overflow bottle is leaking like crazy, steam will come from the top and bracket area and this morning it was pouring coolant out of the ball valve at the bottom even though it's closed.

This is the one I went with:
http://www.jegs.com/i/JEGS/555/511010/10002/-1

The radiator cap I chose is a Moroso 12-16lbs cap.

Should I choose a different overflow bottle? Need to fix this ASAP.

 

This is what I used for an overflow. That overflow you have is not big enough.

 

I have heard 1 qt is plenty but I'm open to ideas. What is that overflow box off of?

 

sounds like you still have air trapped inside your cooling system that is causing it to boil. did you do a vaccum pull down on the system when you filled with coolant?

 

I am not sure what it is off now it has been awhile,seems it was a chevy car.

 

I just ordered one for a later XJ and will try to mount it in the same spot.

I did not do a vacuum pull, never heard of that. I've always just ran open systems with the cap off to allow it to burp for a while.

 

I did mine last year it has worked fine ever since

 

Drove around yesterday with the new bottle and it's working great. It also holds a lot more coolant than it did with the small bottle.