Needing some suggestions my truck has 135k on it its an 05 l33. On start up when the motor is cold it has really low oil pressure bout the first line on the factory gauge at idle is where it will stay untill you give it some gas then it will climb up to 40 and then go back down it also wont go over 40 psi untill it warms up. Now once the motor warms up it will hold 35 to 40 psi of pressure at idle and then it will also climb up to 60 psi at wot. What I'm wanting to know is have any of you ever heard of this happing and if so what would be the first thing to change I'm thinking maybe the o-ring on the pick up tube. But I'm not sure. My only guess is the o-ring shrinks when it gets cold and once the oil gets hot it heat the o-ring up which would make it expand and seal off all the way. Any help is appreciated

 

Misread the post initially-

The oil pickup tube o-ring is an all-or-nothing part. If you're sucking air at startup you would know because every lifter in the engine would be pegging out. Cold start pressure will be more affected by the state of the bearings or lifters, worn parts cause less pressure when cold.

The oil pressure gauge is anything but accurate, though. The only way to know your actual pressure is to use a mechanical gauge tapped off the cooler block or at the existing sensor port behind the intake.