Since you already know what your physical oil pressure is at idle I
would try to get an accurate spec from Ford. if 10psi is normal the the
problem is likely the switch or cluster.
If it is below spec it could be high mileage (normal bearing wear will
lower idle pressure) a weak bypass spring in the pump, or a the wrong
oil filter or oil.
If you are not hearing any "lifter clatter" or knocking when u start it, I wouldn't be too concerned about a bad pump or engine damage just yet.
Use only 5/30 or 10/30! anything thicker can cause cam damage due to oil starvation. Also going to long between oil changes can lower idle pressure as the oil looses viscosity and thins out.
According to factory wiring diagrams 2001 F150 does not have a pressure gauge , it has a warning light, however when I read the test procedure it talks about a gauge. either way, light or gauge, it uses a switch (not a sender) to signal the cluster that oil pressure is either above or below a certain value. again, I'm sorry, i don't know what that value is.
The instrument cluster receives ground through an oil pressure switch. When oil pressure is above a certain pressure the switch closes and the instrument cluster then turns out the light or indicates "normal" oil pressure. if the pressure is below a certain value the switch is open (the circuit to the cluster is not grounded) and the light will be on or the gauge will read no pressure.
The light or gauge is NOT directly controlled by the switch. If it has a gauge the gauge will show an increase in pressure when engine RPM increases (calculated by the cluster) it is not showing true pressure.
if your idle pressure is normal, you can test the by grounding the circuit at the switch, key on, if the light is out or the gauge reads normal the problem is the switch (assuming that physical pressure is above spec).
If the idle pressure is slightly below spec you could try an oil stabilizer like Lucas or STP and keep your oil change intervals to 3500 miles.
I hope this helps, feel free to contact me for more information
Robert Grove, ASE Certified World Class Technician, Automotive Hall of Fame 1996Wego2u Mobile MechanicMobile Mechanics in Orange County, CA
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