Question about 1998 Jeep Cherokee

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98 jeep cherokee - 4.0 L low oil pressure at idle once warmed up

Oil pressure when first started at 40 - stays there even at edle until 15 - 20 minutes pass - then when at idle dips to the 20 - 25 range - but operates at 40 when driving
what do you think is going on - how serious is it? I am preparing to send the car off with my son to Chicago -

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  • dek1957 Feb 21, 2009

    I have a 1998 4.0 XJ 5spd. Runs great! good mileage, everything is
    fine except for this little low knock that is best heard from the front
    seats with the doors closed. The thud (sounds like a rod knock) goes
    away when the engine is first started and the oil pressure goes to
    35+psi. when the engine drops to idle (700-900rpm) the oil pressure
    drops to 5psi and the knock starts and wont stop even if the rpm is
    increased and oil pressure climbs to normal (35+ psi)1000 rpm+. IF I
    shut it back off and restart it and keep the rpm above 1500, there is
    no knock. When I let it idle back down the knock starts in again at
    750-900rpm with 5 psi. One thing i noticed that seemed strange was the
    the pressure would fluctuate 5-14psi at idle with no change in RPM. I'm
    leaning towards a new oil pump, but will get it checked by manual gauge
    first. The spooky thing is the pressure fluctuation and the no knock at
    start up even if I just turn it off and then immediately start it again.
    hummmm? any ideas guys could use the advice.

  • Anonymous Mar 22, 2014

    is this an exhaust manifold problem

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The only spec that Jeep gives for the oil pressure is 37lbs @ 1600 rpm. Since you are within specs I would not concern myself with it. Though with a new oil change you will probably notice a slight increase.
Also beware that the 4.0 is known for bad oil pressure switches.
Tell your son to have a safe trip and don't worry.

Posted on Nov 24, 2008

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It is a serious matter, I advise you to have it checked first before sending it off to chicago. Have your oil pump checked, to explain it to you sir, its like your cars heart is failing.

Posted on Nov 24, 2008

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