Oil pressuare. strange happening!

[rallyjo]

I have rebuilt a 2lt 8v for a rally car. When the car is started it shows 2.5 bar press at idle and goes up to 4.5 bar for the first 5km. After that it drops to 2 bar while driving. This is from cold.

Why is this?? I used a cheap oil for the running in. There are no leaks that could cause pressure drops. I think that it could only be the oil that is losing its properties and that is why it is losing pressure.

Please help??