The Viscosity of the oil definitly has an effect on pressure. I'm running 10W30 in mine. A temp. fix is to use a higher viscosity oil. I ran 20W50 until my new oil pump showed up. Some motor oil additives also increase viscosity. To me this was just a temp. fix. Also do some research on the oil pump drive gear before changing an oil pump out. The main thing is to check it with a gauge.