Jan 092017
 

1995 Jeep Grand Cherokee LaredoI have a 1995 Jeep Grand Cherokee with a 5.2L v8. About 80,000 miles. I recently had an alignment done, and now I am having trouble with my oil pressure. (Probably not related.)
When the engine is idling, the oil pressure is about 2/3 of the way up, and as I speed up, the oil pressure gauge wiggles and twitches, and sometimes drops to about half way. When I drive fast, (60mph or faster), the gauge stays around the 2/3 mark.

What concerns me most is that there is sort of a clicking noise coming from the engine. It doesn’t sound quite like a “no oil” piston slap or whatever, but still it doesn’t sound good.

I had the oil changed after it started, and I’ve checked it several times, and the oil levels are good. Also, no check engine lights or anything, and the engine temp and voltage and idle and everything seem normal.


RESPONSE

The most common reason for odd oil pressure readings would be a failing or faulty oil pressure sending unit.

Oil Pressure Test

Check for proper oil pressure at the sending unit passage with an externally mounted mechanical oil pressure gauge (as opposed to relying on a factory installed dash-mounted gauge). A tachometer may also be needed, as some specifications may require running the engine at a specific rpm.

  1. With the engine cold, locate and remove the oil pressure sending unit.
  2. Following the manufacturer’s instructions, connect a mechanical oil pressure gauge and, if necessary, a tachometer to the engine.
  3. Start the engine and allow it to idle.
  4. Check the oil pressure reading when cold and record the number. You may need to run the engine at a specified rpm, so check the specifications.
  5. Run the engine until normal operating temperature is reached (upper radiator hose will feel warm).
  6. Check the oil pressure reading again with the engine hot and record the number. Turn the engine OFF.
  7. Compare your hot oil pressure reading to that given in the chart. If the reading is low, check the cold pressure reading against the chart. If the cold pressure is well above the specification, and the hot reading was lower than the specification, you may have the wrong viscosity oil in the engine. Change the oil, making sure to use the proper grade and quantity, then repeat the test.

Low oil pressure readings could be attributed to internal component wear, pump related problems, a low oil level, or oil viscosity that is too low. High oil pressure readings could be caused by an overfilled

Oil Pressure Sending Unit Testing

  1. To test the normally closed oil lamp circuit, disengage the locking connector and measure the resistance between the switch terminal (terminal for the wire to the warning lamp) and the metal housing. The ohmmeter should read 0 ohms.
  2. To test the sending unit, measure the resistance between the sending unit terminal and the metal housing. The ohmmeter should read an open circuit (infinite resistance).
  3. Start the engine.
  4. Once again, test each terminal against the metal housing:
    • The oil switch terminal-to-housing circuit should read an open circuit if there is oil pressure present.
    • The sending unit-to-housing circuit should read between 15–80 ohms, depending on the engine speed, oil temperature and oil viscosity.
  5. To test the oil pressure sender only, rev the engine and watch the ohms reading, which should fluctuate slightly (within the range of 15–80 ohms) as rpm increases.
  6. If the above results were not obtained, replace the sending unit/switch with a new one.

Oil Pressure Sending Unit Replacement

oil pressure sending unit

  1. Disconnect the negative battery cable from the battery.
  2. Unplug the oil pressure sending unit wiring harness connector from the sending unit.
  3. Unscrew the sending unit from the engine block.
    To install:
  4. Install and tighten the new sending unit.
  5. Plug the electrical wiring harness into the sending unit.
  6. Attach the negative battery cable.

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