I have not started my 70 396 for 2 weeks , Went to check the water in it ,and when i took off the cap it hissed at me, is this normal to have pressure still in it? Thanks Frank

Yes it is comman, just means the sytem is sealed tight. My racecar is the same way, can get home with it and 2-3 weeks later go look at it, loosen up the cap and will get a hiss.
Duane

I would think this would be air inducing INTO the cooling system? It could make the same hisss but going the other way usually because I am assuming that it is at a cooler ambient temperature?

The ambient temperature of the cooling system last time it was closed was probably warmer. And, I am assuming that you do not have an expansion tank and/or reversing cap either. If you do have an expansion tank, the system should have pulled more coolant into the system and the reading nearer the "cool" mark.

But then again, positive pressure could indicate that the system is just a smiggen warmer than last time you opened it and the cap just hasn't release it.