Your OE gauge is pressure, not temp. Also the OE gauges are not real accurate. They just give you a ball park reading. The thing is if there is a big change in readings. At idle 20 to 40 PSI is normal, and up to 80 PSI at say over 2500 RPSs or so is normal. When the engine is cold, the pressure will be higher, because the oil is thicker when it is cold. So if out of the blue, you see your OP drop to 5 or 10 PSI at idle, or if the pressure sky rockets, then there is an issue. If you go through the trouble of pulling a valve cover, you can see if there is a sludge problem or not. If there is a build up of sludge, then it will be through out the engine. If it is clean under the valve cover, the you can eliminate sludge as an issue.