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Oil Pressure issue

Discussion in '80-Series Tech' started by vt92, Feb 27, 2007.

  1. vt92

    vt92

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    I bought FUELGEDDES' LX-450. (https://forum.ih8mud.com/showthread.php?t=121735)

    Last night, I connected a mechanical oil pressure gage and here are my findings:

    At startup, the pressure is about 60-65 psi
    After one minute, it drops to around 40 psi
    After about five minutes (engine is starting to warm), the pressure is 20 psi.
    After a few more minutes (engine is fully warm), the pressure drops to zero.

    Once the pressure drops, I have noticed that the oil pressure doesn't change much as you increase the throttle.

    I checked the oil level with the dipstick after the pressure dropped to zero. The oil level was normal.

    The power steering assist seems OK. Any recommendations on where to go from here?
     
  2. Waggoner5

    Waggoner5 SILVER Star

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    It will make a lot of difference on where you tapped in for your plumbing as to what pressure you read. Personally I like to read the pressure at the lowest point which is after the bearings. I am not sure where that point is on the 1FZ, but when I built my truck I used aftermarket electric gauges and put the new sensor in the same spot as factory. I get similar readings that you have, but a little higher across the board. I have never seen 0 either. If your pressure is indeed at 0 and the engine is not making any lifter noise because of this, I would try a heavier oil, especially if you have some miles on your truck. Mine has 140k and I run 20w50 year around. It helped my pressure issue immediately.
     
  3. toylndcrusr

    toylndcrusr

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    My oil pressure does this too. I was thinking of putting new main bearings in, and rod bearings while I was at it.
     
  4. vt92

    vt92

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    I put the plumbing for the mechanical gauge where the sender was. This isn't intended as a permanent solution, but just a way to verify the oil pressure.

    The sender was causing the instr. panel gage to read 0 all the time. It seems strange to me that I'm having oil pressure issues and the sender went bad at the same time.
     
  5. RavenTai

    RavenTai

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    replace your oil pressure relief valve & spring and retest.

    what oil are you running?
     
  6. instigator

    instigator

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    i noticed that when i installed my mech. gauge, that it fluctuated alot, so much so that it broke the connection from the bourdon tube inside the gauge. then it read 0 but i was getting a lot higher pressure at startup 100psi plus then dropped down to about 40 when warm
     
  7. vt92

    vt92

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    RavenTai:
    Thanks for the tip, I 'll try replacing the valve and spring.

    Last night, I changed the oil and filter just to make sure there wasn't a problem with the filter. I put Valvoline 10w40 back in. Probably not the best oil, but I didn't want to spend too much since I'm troubleshooting the oil pressure problem and possibly will wind up changing oil several times before I'm done.
     
  8. vt92

    vt92

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    Any thoughts on the possibility of a loose crankshaft bolt? Could it cause this behavior? Could there be more slippage as the engine heats up?
     
  9. landtank

    landtank SILVER Star

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    I think people who have had a loose crank bolt usually see problems with steering effort first.
     
  10. DTAYLOR

    DTAYLOR

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    Rick,

    What is the actual mechanical issue going on when the crank bolt gets loose, or is not properly torqued, as it relates to steering assist? Oil pressure?

    D
     
  11. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    The oil pump drive gear on the crankshaft is clamped in place by the crank pulley. It is not keyed or taper fit, hence the reason for the 304 lb-ft of torque required to secure the crank pulley. If the crank pulley is loose the drive gear will slip, resulting in a loss of power steering assist and oil pressure.
     
  12. Waggoner5

    Waggoner5 SILVER Star

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    There you go Dan. 2 birds with 1 stone...
     
  13. dd113

    dd113

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    I know all about this motor, what has happened to it, some thoughts on what caused it and more than a few ideas on where to go with this issue.

    I doubt the PO told you the work we did on it and the conclusion we came to.

    PM me
     
  14. dd113

    dd113

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    How can you fit your pudgy arms down in there to check?
     
  15. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    Have you been peeking?



    :eek: :lol:
     
  16. DTAYLOR

    DTAYLOR

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    Makes a lot of sense..

    The torque on the crank bolt sounds like my problem. I have low oil pressure, low PS assist, and a slow crank like the timing is off.

    Now to find a torque wrench that will go up to 305 ft lbs.

    D
     
  17. Waggoner5

    Waggoner5 SILVER Star

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    Thats good info. I had no idea this would cause what it seems to be causing.
     
  18. landtank

    landtank SILVER Star

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    The sprocket for the timing chain is keyed so even if the bolt isn't tight enough to adequately drive the gear for the oil pump and PS pump your timing will not change.