Well After an AutoRX run I switched to Chevron 10W-40 for a rinse phase. Yesterday I drained out the Chevron and filled back up with Schaeffer's 15W-40 Blend. Well I noticed something different with the Schaeffers over the Chevron. After driving 30 mins on the highway my oil temps were the same with both oils around 200-210 degrees but I noticed a vast difference in oil pressure between the two oils. The Chevron 10W-40 would drop to 30psi at hot idle, oil temp 200-210 while the Schaeffers would only drop to 40-42psi at same temp hot idle. What could cause the oil pressure difference between the two? Both oils produced the same pressure under load 50-55psi. Vehicle in question is a 2000 Jeep Wrangler 2.5L I4 lifted, locked and ready to rock! Very heavy TJ loaded down with many aftermarket accessories and has 4.88 gears which makes the little 4 squirells turn 3000rpms at 70mph.