What is the correct oil presure on a 1994 306 xsi 2.0 ltr ?.

I think  I need a new presure sensor because when i start the car (hot or
cold) the presure display on the
dashboard jumps to max 8 bar if i turn the car off and on again i`ll get 6
bar on/off again i`ll get 4 bar?.

when driving about 70 mph the engine will be at +/-4000 rpm, oil presure
sometimes is 8 bar
but mostly between 6-7 bar.

Is this normal ?.
Do i need a new sensor or is a new filter and oil change enough.

Thanks
Bren