Oil pressure Iltis
 

I have a question ..... if I have driven a few kilometers with my ex. Can. Iltis tends to hit the oil pressure gauge to 8 to 9 kPa x 100. This happens at a speed of 80-85 km / h and the motor at operating temperature. The outside temperature is then about 28 degrees Celsius. If I stop the car, stop the engine and then I start the engine again, after about 30 seconds, the oil pressure is normal again stationary about 2 kPa x 100. Normally, this pressure is around 6 to 7 at 85 km / h. Also swabs the needle occasionally back and forth. The oil level is correct and I use motor oil 15W40. The engine runs perfect, no strange sounds! Can the oil pressure sensor be the problem?
I hope it's nothing special because I want to go to the International Army show in Enschede next week.