Have seen a few threads pop up lately across the forums on low pressure indication on the dash oil pressure gauge.

This thread will summarize the possibilities and provide some troubleshooting tips (and links to DTR videos).

Possible causes (easy things first):
Low oil level
Low battery voltage
Bad oil pressure switch or wiring
Damaged or misaligned oil filter or aftermarket oil filter/cap (causes issues w/ anti drainback valve or filter bypass valve)
Stuck open pressure regulator
Inaccurate dash gauge
oil dilution (due to fuel)
Missing gallery plugs
"Early model years (03 and 04.25) - missing check valve ball in the HPOP
05 and up model years - badly leaking STC fitting on the HPOP"
Front cover gasket leaks
Scored/damaged oil pump or front cover
Restriction in the pick-up tube or oil pan
Missing bearing shell(s)
Broken or damaged piston cooling jets

Troubleshooting:

First verify proper oil level (when doing this keep in mind that fuel dilution of the oil will cause a rising oil level, and the oil MIGHT have a slight diesel smell).
Then verify that you have the proper OEM cap.
Next, charge the batteries and then load test them individually.
Then inspect the oil pressure switch and wiring.
If all that looks good, then pull the oil filter and inspect it. It should be an OEM filter and not be damaged (improper filters can look squashed or twisted).
Verify that your oil filter is properly soaked with oil - it should be covered from top to bottom with oil that drips off.
Push down on the drain valve and verify that it moves up and down smoothly. Also inspect the oil filter standpipe and check for broken plastic parts.
Then verify that the oil filter housing will fill at a proper rate. 10-12 seconds to fill if you don't depress (close) the drain valve. 3-4 seconds with the valve depressed.
To do this test, leave the key out and use the starter wire circuit to crank as described below:

There is a "yellow with light blue stripe" colored wire adjacent to the passenger side battery in the engine compartment, near the vacuum pump that has a "squeeze-and-pull" type connection. Disconnect it, and jump the male end of the connector to the passenger side battery positive terminal. The starter should crank when you do this (but you wont try to fire injectors).

If all that looks good, you might want to replace the switch part # F81Z9278AA (be VERY careful pulling this switch and installing the bew one. The threads do not go in very deep and you can easily crack the oil cooler cover if you screw on the new switch too tightly), or you can verify that the oil pressure regulator looks good (no scuffing or galling) and operates smoothly. You need a 12MM hex bit to pull the regulator.

According to DTR, the batteries being in good shape is important because the gauge is on the end of the 5V circuit and low batteries can affect the dash reading.

If you want to verify the base oil pressure, the following can help:

The oil pressure switch activates at 5 psig. 12 psi at 700 rpm is minimum recommended (24 psi at 1200 rpm and 45psi at 1800).

The oil pressure switch requires a 1 1/16" (or 27mm) socket to remove. Oil pressure switch thread size: 7/16 x 20 tpi (weird I know, but I believe this is the correct size - please verify yourself as there is a lot of controversy on this).

Note 1 - the threads do not go very deep in the oil cooler cover for the oil pressure switch and it is aluminum. It is easy to crack. Be careful, and do not tighten very much when installing a new sensor.

Note 2 - The oil pressure switch plays no part in starting. The PCM doesn't use that information.

I edited the original post because of so much controversy on the oil pressure switch threads. I have not located an adapter for it to add on a manual gauge. After research and thought, adding a manual gauge would add too much weight and might contribute to cracking the cover. This is not recommended! Some other options for a manual gauge are mentioned below.

LPOP regulator part #: 3C3Z-6C751-A, Regulator o-ring part #: W302722

Oil filter housing drain valve . The oil filter keeps this valve closed. Part # 3C3Z-6800-A

There is also an oil system "anti-drain back valve". This is a check valve in the oil filter base that keeps the high pressure oil system primed. It is would not play a part in low base oil pressure.

If you have good oil flow of low pressure oil to the filter, and feel that the pressure is actually good (or verified it w/ a gauge), and you are experiencing no engine performance issues, then investigate the dash gauge for the problem.

If you have good flow of low pressure oil to the filter, and feel that the pressure is actually good (or verified it w/ a gauge), but are having engine performance issues, then look at the HPO system - specifically investigate the possibility of a big leak in the HPOP system (IPR wide open, STC fitting failure, early model HPOP "ball-bearing plug" missing, etc).

Hopefully you have resolved the issue after the above troubleshooting. If not, you will have to dig deeper - probably the next step would be to inspect the LPOP (pull the front cover). If you see damage from foreign object(s), be sure to identify the cause before reassembly (injector clips, lifter needle bearing failure, etc). I have read that over-revving an engine (say over 4200 rpm) can cause damage to the LPOP. I won't include any more discussion on that because it can get lengthy!


Resources: DieselTechRon (DTR) videos and WSM



I think the best way to get a manual pressure reading is by buying an oil filter cap with a test port in the top. I have seen threads about installing a tee below the oil temperature sensor, but that might affect the temperature reading.

https://www.accuratediesel.com/shop/...FcO3wAodec0P6w

You can also install a manual gauge in the oil pressure test port, but it requires more work than I feel is justified for what normally is wrong. However, it is handy. Thanks to "TheBestKindOfEx" for his thread on this subject:

https://www.ford-trucks.com/forums/1...test-port.html