OVER HEATING WITH A 318 ?

First off you need to verify that the engine temperature reading 185 was correct. As stated what size overflow bottle are you using? I have a overflow bottle that holds about a quart of coolant. I keep about an inch of coolant in the bottle when cold and when hot the expansion of the coolant makes it about half full. (Using Standard AF) The pressure cap has nothing to do with the expansion and contraction of the coolant, it raises the boiling point of the coolant which in your case is not necessary as the Evans coolant doesn’t boil till over 300*.