Just bought my first Dodge Diesel. It is a 2004 24v 4X4. I have a question regarding the oil pressure. When I start it cold, the oil pressure goes up to 40+ and stays there until the thermostat opens and when I let off the accelerator or slow down to stop. The oil pressure goes down. It does stay within the safe zone. But from what I have heard, it should stay at or above the 40 at all times. What do I need to fix? thank you