"Check engine" light kicking in at 4-5k rpm

[Jezza_hr]

On the way to Japfest today my car seemed to show an interesting problem. The 'check engine' light kicked in on the motorway at 5k rpm (if I drop down below 4 it dissapears) Looking to the oil pressure and water temp read outs, the water temp is normal and the oil pressure sits a tad higher than normal.

Once we got to Japfest we were a bit stumped as to what it could be. I checked the radiator and it's boiling hot at the top and cold at the bottom. I squeezed the rad pipes and they had very little pressure in them, so my initial guess is that it's a faulty thermostat or water pump.

However, what I dont understand is, why is only the oil pressure going above normal and not the water temp? the water temp sensor seems to show normal readouts like I say. Could it be that the water in the engine is just enough to show a cool readout yet the engine oil is getting hot enough to show a pressure hike? im a bit confused