Coolant System Mysteriously Pressurizing

[danc30]

Why would my coolant system get pressure in it while just sitting in the garage?

Car hasn't been started in more than 2 weeks. All of a sudden coolant started slowly dripping out of the overflow tank/tube.

I took off the radiator cap and there was a lot of air/coolant under pressure. Refilled and replaced cap, started dripping again and again, there was quite a bit of pressure in the system when I took the cap off again. I am assuming tthe system is getting up to 16lbs and letting the coolant to get past the pressure cap. My overflow and surge tank are lower than some of my other hoses and about centered in height with my engine. Meziere said it should be OK. It was for the first 2000 miles also.

I currently have in the system:
90% distilled water
10% anti-freeze
1 bottle water wetter\
1/4 ounce of tracerline UV dye. (helped me find a leak)

The Tracerline says it can be left in the system without harm. Funny thing is, this pressure thing started shortly after putting the dye in.

Could it be something other that the dye?

Any and all help is appreciated.
Dan