Re: overheating. Verify the condition of the oil, pull a little out and feel, smell and check if burnt. If flash point is reached the oil is too hot, at the temperature you are running at, touch the conduits to and from the rad, can you keep a hand on it for a few seconds, if not it may be too hot. The pressure cap maintains a + pressure within the system and then when cools the coolant will travel into the reservoir, is the reservoir too high or too low.