Question about 1988 Ford F 150

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5.0 L Oil pressure drops once engine warms up

The oil pressure drops off once the engine warms up. I have put in a new oil pump and pickup, tried various grades of oil (including fully synthetic), used Marvel Mystery Oil then changed the oil and filter. Once the pressure drops the engine will sometimes sound like the bottom end is rattling

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  • Ford Master
  • 21,873 Answers

Sounds like the main bearings are probably going.
Did you pull a couple of caps and look at the bearings when you had the pan off ?
It could be dirt in the passages but probably wear on the crankshaft.
As oil warms up it thins out and pressure is lost thru gaps in the bearings.

Posted on Sep 07, 2012

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5 Suggested Answers

hondakilla

Donald Holt

  • 129 Answers

SOURCE: oil pressure keeps dropping?

You'll have to drop the oil pan and you will see your oil pump...Not much to replacing it either the hardest part is dropping the pan good luck and have fun wrenching...

Posted on Apr 25, 2010

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fokineguy

  • 4 Answers

SOURCE: oil pressure

Check the oil pressure switch!

Posted on Jun 14, 2008

MrScary66613

Travis Humphries

  • 1990 Answers

SOURCE: Oil Pressure Gauge/Engine rattle 2000 Ford Explorer 4.0 6cyc 4wd

Your Oil Pump is Out and will need to be Replaced. This is not a Job that you would want to attempt on your Own unless you have been a Mechanic. Trust Me. Been an ASE Certified Mechanic for 35 Years.

Posted on Jan 22, 2009

Anonymous

  • 18 Answers

SOURCE: low oil pressure at idle

how low does the oil pressure drop?? is it below 40?

Posted on Mar 05, 2009

Molson02536

Harvey N Tawatao

  • 3854 Answers

SOURCE: oil pressure problem

You oil pressure sending unit has gone bad, it's common to go bad and some even leak oil. 
The oil pressure sensor is on the back of the block on the passenger side, you can get to it from the top and not from the bottom. There are (2) switches back there that screw in to the block and you can only see it from the top of the engine. The Oil Pressure Sending Unit is the one wire harness with a green and white strip on it. The other switch has more wires to it. 
When you pick up the new sensor, make sure you get the right one. make sure you get the Oil Pressure Sending Unit which sends variable oil pressure and has only one quick connect for the wire connector. The oil pressure switch is the one that only activates the oil light on older engine
Once you get the right part at Auto Zone for around $9.00, disconnect the wire clip with the green with white strip on it. and use a deep spark plug socket with a extension and u joint to get the sensor out. The sensor comes with teflon tape already and no oil should leak out from the block. It as simple as replacing a bolt and reconnecting the wire connector. 
Good luck and hope this helps, take no more then 10 min to do but about 5 hours for the engine to cool off LOL

Posted on May 29, 2009

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1 Answer

Oil pressure drops at slow speeds while in gear


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.

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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.
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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.

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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.

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