'98 12v has sat for a few days so is totally cooled off. I went to check the radiator coolant, when I unscrewed the radiator cap it was under a fair amount of pressure even through the fluid is cold.

Any suggestions?

 

Not to be insulting, but are you SURE it was pressure and not air running the other way?

If it was in fact pressure, start it and look for coolant bubbling. Smell the fill hole for exhaust in the radiator. If the coolant is bubbling, and/or you smell exhaust, then you almost certainly have a blown headgasket.

 

Pull the radiator cap, check that the vent is not stuck - that small stainless cap in the center of the rubber gasket.

Make sure it's free to move - if not, replace the cap