I had a similar issue last year on my Plus8.
There are 2 oil pressure senders and the one to the gauge was playing up.
From cold it showed correct psi but after a couple of miles it went way up to the top of the gauge. Always ok from from cold but when some heat got to the oil it resulted in this happening. Simple job to replace and now ok.
The engine has a second pressure sender for the ecu so no worries with oil as the ecu would have shut the engine down if pressure dropped.
For the V8 normal psi is about 40 psi or 3 bar.
It drops to just above 15psi(1bar) on idle which causes worries until you realise that is normal!
