There's nothing wrong. Your engine has tight bearing clearances. The oil pump is exceeding engine demand at 1200 RPM and higher. The relief valve is set to 45 psi. When cold, the oil doesn't flow well, so the engine demand is reduced and the relief valve opens.
Remember that the oil pressure is being measured at the pump, not at the most distant bearing. You can be reading relief pressure at the pump, but be near zero pressure at the most distant bearing due to high viscosity oil.
At your next oil change switch to 5W30 viscosity. Oil viscosity has been discussed numerous times in the past. The general rule is to use the LOWEST viscosity oil that produces adequate oil pressure. Since 95%+ of engine wear occurs at and just after startup, its important to get the oil flowing as quickly as possible. A lower viscosity oil will do that. 10 psi at hot idle and 10 psi/1000 rpm is the general rule minimum pressure.
If you're worried about ZDDP concentration, you can use Mobil-1 0W40 European Formula, which still has ~1200 PPM ZDDP.
Also, you can't tell if the oil requires replacement by looking at it. Only a lab analysis can determine the state of the oil. Spend the money for an analysis at Blackstone (~$35 for basic analysis plus TBN, and postage). Depending on the results, you may be able to extend your oil change interval. (I'm currently running 15,000 mile interval on a 2000 Safari van 4.3 V-6, with filter change at 7,500 miles). The analysis will also give you advance warning of developing problems.
Ken
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