[rustyBob]

Your cooling system will seek a level that it will operate at when you are doing normal driveing.....one or both of those caps should have a little valve on the bottom of it (if its a recovery style cap)that will let coolent out when pressure builds and then let it back in when the coolent cools off( expansion and contraction)if you dont have an overflow bottle then your coolent(when it expands)will pizz all over your floor....if you have an overflow bottle the the coolent that is in the bottle will draw back into the rad. when it cools(contraction).........ok......and it dosent make any sence to have 2 caps to begin with.