I have a 2000 dodge b3500 full size cargo van with 510,000 miles and recently noticed that the coolant in the overflow tank was disapearring quite rapidly. In four days I refilled it twice. No visible leak on or around engine compartment, oil is not milkshake like, no noticeable white smoke coming out of tail pipe. Also a couple weeks ago I had a leak at the top of the radiator. I brought it to a small repair shop which the mechanic just put stop leak in it the leak was very noticeable before and after he put that in the leak seemed to have stopped. Could it be that it wasn't completely sealed but then also wouldn't I be able to notice any wetness around in the compartment?