What oil properties make a difference in a valve timing control systems? According to the service manual for my car, "the intake camshaft pulley position is regulated by oil pressure, which is controlled by the valve timing control solenoid valve." The manufacturer recommends 10W-30 up to 20W-50 oil depending on ambient temps. So my question is what difference would it make in a valve timing control system using different weight oil. What if I used a 5W-20 oil as opposed to 20W-50? Thanks for any input.