Ok so I have finally tracked down the source of my coolant leak in my 2005 CTT. I have already replaced all the pipes, waterpump, thermostat, T's etc. The expansion tank was replaced 20k miles ago.

The expansion tank maintains pressure. When driving long distances, on level ground like going West across Texas on the I-40 there is no coolant loss even with spirited driving etc. When driving in East on I-40 in Tennessee with the hills and mountains, when going up a steep incline at decent throttle I can see coolant splashing on the ground in my rear view (a significant amount!) 100% of the coolant being lost is coming out of the overflow hose from the expansion tank as evidenced by the where I can see the wet areas and the UV flashlight has directed me. Its like the car has tipped enough to where the coolant is reaching the overflow line. Is this because perhaps the cap is not maintaining ENOUGH pressure? The cap was replaced about 30k miles ago. Please help its driving me crazy

 

I think if it was the cap not holding pressure, your coolant boiling point would get far too low and it would boil over no matter what the incline or situation I think this would happen just holding it at 2,000 rpm in your driveway for a few minutes.

I can't offer any other suggestions beyond that, but it's for sure a strange issue and you're right, being able to see the coolant coming out on the road while you're driving means it's a substantial amount being lost.

 

The caps can be had in almost any auto store - they're identical to VW caps. I'd suggest replacing it.