5.0 L Oil pressure drops once engine warms up

First I ask, how many miles on the engine and what size engine is and the vehicle its in. Lots of things factor in here, like did you tell the dealer to replace the pickup tube or is that their solution to the problem? Was the oil pressure actually checked w/ an independent mechanical gauge ? If so how did it compare to book specs? If it was checked and the pressure was low the oil pump should have been replaced as well. If problem does exist w/mechanical gauge then a further teardown may be needed to inspect the oil pump itself, the main bearings and camshaft bearings for excessive wear. Depending on whether the engine has over 100,000 miles on it, this may not be a bad place to start looking anyway.

see this tips and fix it. God bless you
The oil pump supplies oil to lubricate your engine. If the oil pump is worn or is not turning, the engine will suffer a loss of oil pressure, which may result in engine damage or engine failure.
The first sign of trouble may be a low oil pressure warning light, a drop in the normal reading on you oil pressure gauge (if your car has one), or the appearance of ticking or clattering sounds from your engine.
As a rule, most engines only need about 10 PSI of oil pressure for every 1,000 RPM of engine speed. Oil pressure will read higher than normal when a cold engine is first started because the oil is thick. Oil pressure will gradually drop as the engine warms up and the oil thins out. So normal oil pressure on a warm engine cruising down the highway is typically 30 PSI up to 45 PSI.
SYMPTOMS OF OIL PUMP TROUBLE
The first thing you should do if any of these symptoms occur is to stop your car, turn off the engine, let it sit for a few minutes, then check the oil level on the dipstick. If the oil level is at or below the ADD line, add a quart of oil to bring the level back up to the full mark. Add as much oil as is needed to raise the level to the full mark. Then restart the engine. If the warning light remains on, or the oil pressure reading does not climb back up to its normal range, or the engine noise does not go away, you may have a bad oil pump.
The other possibilities include a bad oil pressure sending unit, or a problem with the oil pressure warning light circuit or oil pressure gauge.
OIL PRESSURE SENDING UNIT
If the engine is NOT making any unusual noises and seems to be running normally, and the oil level on the dipstick is FULL, but you are still getting a low oil pressure warning light or low gauge reading, the fault could be a bad oil pressure sending unit.
The oil pressure sending unit is mounted on the engine block. On some applications, there is a spring-loaded pressure-sensitive diaphragm with a switch inside the sending unit. This switch completes the circuit to the low oil pressure warning light if oil pressure drops below a certain threshold. The unit may stop working if the diaphragm inside fails, if the switch is stuck, if the small hole that allows oil to enter the sending unit becomes plugged, if there is a loose, corroded or broken wiring connector at the sending unit, or there is a fault in the wiring circuit between the sending unit and warming light.
On vehicles that have an oil pressure gauge (electronic, not mechanical), the oil pressure sending unit has a small rheostat inside that sends a variable voltage signal to the oil pressure gauge when the diaphragm moves. A worn spot on the rheostat or any of the other problems just described for the simple pressure-type oil pressure switches can cause a problem.
FORD'S FAKE OIL PRESSURE GAUGE
On many Ford vehicles that were built from 1980 through the 1990s, the oil pressure sending unit has two switches, a low pressure and a high pressure. These vehicles also have an oil pressure gauge, but the reading on the gauge is not a true indication of real oil pressure. As long as the pressure to the sending unit is between high and low, the gauge will read normal. If oil pressure drops and trips the low pressure switch, the dash gauge will now read low. Or, if oil pressure goes up and trips the high switch inside the sending unit, the dash gauge will read high. Consequently, don't rely on the oil pressure gauge for an accurate reading in these vehicles. It is only a gross indication if the oil pressure is low, normal or high.
OIL GAUGE PROBLEMS
If the engine is NOT making any unusual noises and seems to be running normally, the oil level on the dipstick is FULL, and you have replaced the oil pressure sending unit but are still getting a low oil pressure reading on the dash gauge, the fault could be in the wiring circuit between the sending unit and gauge, or the gauge itself might be bad.
Check the wiring connections on both ends as well as wiring continuity between the sending unit and gauge. If no wiring faults are found, hook up a pressure gauge directly to the oil pressure port on the engine and check oil pressure with the engine running. If the engine-mounted gauge shows normal oil pressure but the dash gauge is reading low, the problem is a bad dash gauge.
On the other hand, if the engine-mounted pressure gauge reads low and you have done all of the above, chances are the oil pump is worn, or it is not picking up enough oil because of a restriction or blockage in the pickup screen in the bottom of the crankcase.
OIL PUMP PICKUP PROBLEMS
The pickup tube has a screen on the end to prevent large chunks of anything bad that ends up in the crankcase from being sucked into the pump. But we are talking BIG chunks of debris, not normal wear particles or carbon or dust or other microscopic-sized abrasive particles that can cause pump wear over time.

A failing oil pump.. but more likely a clogged pickup tube or screen.. can cause this once you get above a certain rpm..the pump can't keep up with demand so to speak. .

Drop the pan..clean the pan..inspect for solids etc.. .. remove the pickup tube/screen.. clean or replace the pickup tube and screen..those parts are generally pretty inexpensive.

Of course it could be the sending unit.. or a bad ground/short.. yet depending on how well the rig has been maintained..or operating environment.. sludge and solids blocking the pickup tube and screen could be the culprit.

It would never hurt to drain and drop the pan.. new gasket.. new pickup tube and screen..clean the pan.. new filter.. new fresh oil.. some recommend sea foam... just follow the directions.

Best of luck!

The first stop is to measure the pressure with an external gauge. if the readings are the same, surgery is needed, I would look at the oil pressure relief valve for foreign particles.

It takes resistance to make pressure, and your decsription does not sound good. If the pressure is actually dropping, and you find no issues with the oil pump and pick up, you need to measure bearing clearances... Essentially, everywhere oil is pumped needs to be inspected...

If your oil pressure gets to low it can turn off the fuel pump. This may also have saved your engine. The ECM turns on the fuel thru the fuel pump relay for about 5 seconds. When engine is running oil pressure sender supplies the voltage to the pump. When engine shuts off check oil pressure and voltage to fuel pump.

YOU MIGHT HAVE THE WRONG WIEGHT OF OIL

Check the oil pressure with a test guage, if the finding are the same, the look at your oil filter, pump, pickup, or pressure relief valve.....

Hi I am Vortash sounds like you have one of four problems either the oil you are using is inferior and you need to upgrade to a better one synthetics are best ..
Your Oils pump is failing reducing the oil pressure ..
Leaky gaskets allowing pressure to ecape .
Or more drasticaly your main bearing shells are wearing giving the the oil more ways to escape under pressure . this is usually discernable by a knocking or rumbling noise especially on tick over .. hope it is just the oil for your sake regards Vortash

the oil pump pickup could have come off the oil pump, but u could fell it inside the pan through the drain plug, that is possible, but not very likely, try installing an aftermarket high volume oil pump, most are adjustable for either high volume or high press, you want volume.

Hi! The problem you are outlining is very similar to the Rover V8 (Buick engine). We Brit's are used to the low oil pressure when warm. I presume a complete oil change engine flushed with new replacement filter has been carried out? Maybe a top quality synthetic oil with additive may help. You may take it a little further and replace the oil pump with an after market performance up rated one. If you really are worried about low oil pressure damage whilst in low rev's try Molybnenum Disulphide an oil additive which really reduces friction metal to metal wear particulary in the situation you are describing.
That's the best I can suggest at this moment.
Good Luck! and Happy New Year!
Paul 'W'
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