Hi. Got an 1984 240 GLT and the oil pressure is 4.5 to 5 when cold, whether at idle or crusing down the road. However, after you drive the car a few miles, the pressure drops to 4 while driving, which seems okay. But when you stop the car at a light and it idles, it can drop to 2.5 and stay there until you put your foot on the gas and the revs climb, then the pressure will shoot back up to 4. As long as the tach is above 1500, even on a hot engine, the pressure will remain at 4, but if the tach drops below that due to either speed or stopping the car, it can fall to 2.5. I've got about 220k miles on the car and currently using 10w-30. Should I switch to a heavier oil? Perhaps 20w-50? I live in Escondido, California and it gets really hot here (95 today).