Jeep Liberty Oil Pressure Sending Unit

rickc38rickc38 Member Posts: 20
Our 2004 Jeep Liberty has a problem where (usually when cold) the low oil pressure indicator will illuminate but when you shut off the engine and restart it will shut off. Is this a problem with the sending unit sending an incorrect code? Or maybe the oil pressure could be low? I'm seriously thinking of getting a gauge and testing the pressure. I know low oil pressure can mean BIG problems. I don't want to know about engine bearings being bad. But I know when I change the oil it takes a few seconds for the new oil in the pan to get to the crank because the engine ticks a bit for a few seconds. I've even tried putting oil in the new filter to "prime" it and it still seems to do the same thing. I don't like to hear those noises when I change the oil probably causing some unneeded wear. Any help would be greatly appreciated. -Rick


  • caribou1caribou1 Member Posts: 1,354
    I can see two things:
    - either the ECU does not change the status of the "at pressure" bit (low probability) and sends an engine malfunction alarm,
    - or you may have a leaking check valve (oil filter bypass) that lets the pressurized oil return into the sump via the pump after a few minutes when the engine is not running.

    The absence of oil film normally explains the ticking sound of your engine but if you use mineral oil that is at the end of it's life, the engine will produce the same sound. This is a typical 4 stroke lawn mower engine issue: my wife doesn't know there is oil in there, she just pushes the thing :blush:
  • rickc38rickc38 Member Posts: 20
    No I don't use mineral oil. I always use new oil every 3000. But the check valve idea is a possibility though. But doesn't the check valve bypass the filter when it is clogged when the engine is running? I always use a new filter when I change the oil. Because if it was the sending unit sending an incorrect code wouldn't it signal the MIL light? I'm thinking about getting myself a scan tool and see if any fault codes come up even though the check engine light (MIL) isn't on. Might have something in memory.
  • caribou1caribou1 Member Posts: 1,354
    If you put in series:
    sump * pump * check valve-&-filter * engine

    when the check valve cancels the filter you may get:
    sump * pump * engine

    I think the time and pressure needed for the oil to circulate backwards through the filter is long enough to give you a noise free start even after a few hours.
  • rickc38rickc38 Member Posts: 20
    Ok that is true but if there is oil available in the filter it should start pumping right away. I mean there are no problems with oil pressure as far as I can tell after the oil is changed just that initial start after I have changed the oil and the pump pumps oil back into the system. That's the reason I tried filling the filter so that crucial time when the filter is filling up is eliminated. I don't know if the bypass will allow oil into the main gallery while the filter is filling up I don't think so.
  • caribou1caribou1 Member Posts: 1,354
    You would be surprised to see the time and initial effort it takes for oil to go through a dry membrane. Once the oil made it's way, it's purely friction. Before penetrating the filter it's a surface tension problem, and oil is repelled.
  • ticailleticaille Member Posts: 2
    We have a same problem with my Liberty 2005 Renegade ... Can you have resolve your problem ?
  • rickc38rickc38 Member Posts: 20
    Wow this is an old thread I had to go back and read the other posts from before to remember what was said. We still have the Jeep and it still does the same thing. Its usually when it gets colder it turns the oil light on and I have run 5W30 and 10W30 and it makes no difference light or heavier oil. What I am going to try now is running an engine flush on the next oil change. I am thinking there is sludge in there slowing down the oil coming from the filter into the main gallery. Other than that we are about ready to trade it in and it has over 140,000 miles and we never had any problems with the motor.
  • ticailleticaille Member Posts: 2
    Ok thanks . I want you to keep me if ever you find the problem because we seem to have exactly the same. I am looking for the solution also with my mechanic so I know you care.
  • gary1938gary1938 Member Posts: 1
    edited December 2011
    I was having problems with the oil light coming on when I was sitting idling, I always kept the oil at the full mark and it was using oil not leaking. I reduced the oil level to 1/2 full on the stick and the light does not come on and is not using any oil now.
  • firebatfirebat Member Posts: 1
    I have a 2004 Liberty Renegade. Exactly the same problem - on cold days, cold start, oil light comes on. Shut engine off and restart and light goes off and stays off. Had this problem for years now - but only when cold weather approaches.

    Just had mechanic replace oil pressure sensing unit and still have the problem.

    Some of you have mentioned a "switch" - is there a switch that bypasses the oil filter on startup to get oil to the engine immediately?

    Since the light goes off on an engine restart (every time) I don't worry that much about it - but it is a nuisance.

  • Sdsu329Sdsu329 Member Posts: 1

    Guys. I Have the answer to solve this issue
    1 of 2 things is wrong. 1: the connector to the oil sending unit/switch is faulty. Or 2: need to flush or clean the sludge with kerosene/ engine flush. These videos will help you solve problem. If not these two issues then it’s oil pump or engine crankshaft is worn out. Best of luck!

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