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Oil pressure

Discussion in 'The Garage' started by Muddytazz, Jun 7, 2005.

  1. Muddytazz

    Muddytazz 1 ton status

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    Either my oil pump is going out or the gauge is. I bought the burb 3 1/2 yrs ago and its been doing this since I bought it, but never really put 2 and 2 together that something was wrong :doah:

    Anyways, when I start the burb up in the mornings with a cold engine I have normal oil pressure (or so I think) and after it warms up and I'm driving around, it reads normal (again, or so I think). Here's what it looks like during warm-up and while driving...
    [​IMG]

    As you can see by the needle, is that normal oil pressure?

    Here is what the needle does when I come to a stop, at idle after the engine warms up...
    [​IMG]

    Any ideas here? Is it the oil pump or the gauge or something else?
     
  2. dontoe

    dontoe 3/4 ton status GMOTM Winner

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    My .02..............stick a Autozone (or whatever) mechanical gauge on it to test.
     
  3. diesel4me

    diesel4me 1 ton status Premium Member

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    Ditto!

    What Dontoe said!..if it acts the same way with a mechanical "test" gauge, its likely the bearings are getting a bit loose,and the oil pressure drops when the oil gets up to operating temparature and loses some visosity..

    Stock GM "electrical" gauges are often innacurate!--I once pulled my hair out on my El Camino I had to find out why it was "undercharging"--after trying a known good altenator,running new wires,etc,I found if I pressed on the plastic cover over the dash gauges,my voltmeter would go up 3 volts.to NORMAL!! :mad: --it was a loose connection to the gauge in the dash's printed curcuit board!.... :screwy: --nothing wrong with the charging system at all! :surepal:

    Do you ever hear any noises from the motor after a cold start,like after sitting overnight??...if you hear a "woodpecker" type rattle for a few seconds,thats a dead giveaway the bearings are getting loose..old engines often rattle that way until the oil gets to the bearings and fills in the "gap"...

    But I've seen the oil itself do the same thing--some brands get thin and lose their viscosity more than others..I had one customer at the parts store complain his corvette had the exact symptoms you described after changing his oil to Amalie brand..

    .He bought 5 qts of Castrol 20W50 and changed the oil and filter again,and showed us the results..sure enough,his gauge read much higher with the castrol oil VS the Amalie,even after it got hot driving it 30 miles !...my boss gave him the oil and filter free after he saw it for himself,but never really believed the oil was inferior....neither did I...I've had lots of motors that had low oil pressure,and it made little difference if I had 10w30 or 20w50,or even straight 30w oil in them--still had the same readings on the gauge,MAYBE 5 lbs more if anything...I ran them for years pretty hard,and never blew any of them up too!.. :crazy:
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    If it's been doing this for some time, I'd suspect that it's not really got 0 pressure when hot! :)

    What type oil do you run? You could always put 20W50 in there if you run something like 10W30 now, and see if your pressure readings change.

    Both of those readings are low though, cold or hot.

    I'd be inclined to swap out the oil pressure sender or test it with another known "good" one before blaming the gauge itself. Since it moves, I doubt the wiring/gauge is bad. You very well could have low oil pressure, but 0PSI, your engine probably wouldn't last more than a couple of hours.
     
  5. kennyw

    kennyw N9PHW Premium Member

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    Your still driving your old tired motor too right? He didn't mention it, but his motor has something like 300K miles on it. I'd say all of your bearings are shot and you have too much clearance to hold any pressure. Time to get your new motor done and in if you can or you will loose something soon. It would not hurt to check it with a cheap new or known good mechanical guage just to verify the problem though.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    300K?

    Yeah, I'd just pull that sucker while it's still working, instead of pulling once good pieces out. :)
     
  7. Beast388

    Beast388 1/2 ton status

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    The old rule of thumb for an SBC is 10psi for every 1000rpm. If the engine starts cold with no audible noise, then I would suspect the gauge. Do as the others have recommended and get a mechanical test gauge to check yours. At least that will possibly eliminate one culprit.

    As a reference, my 388 will peg 80psi on start up with 10w40. Once the engine is warm, I have 25psi at 800rpm idle. As soon as I hit the gas, the pressure goes up the 60psi and pretty much stays there as long as I am not idling.

    If your engine has 300k miles, then I might do as Dorian recommended and yank it before it ruins the crank. :)
     
  8. Muddytazz

    Muddytazz 1 ton status

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    Kenny is right, I did forget to mention that this motor has well over 300K or so I guess from what the PO told me when I bought it and the estimated mileage I've put on it (hence my speedo cable has been bad since I've owned it).

    Also, the gauge in my burb now is the stock mechanical gauge. And yes I do hear a woodpecker type of knocking sound for a few seconds ONLY when its started cold.
     
  9. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I highly doubt you have zero oil pressure when idling. Once you get below about 15 psi the hydraulic lifters will start to make noise since they are no longer pumped up. As has been previously said, check with a known good mechanical gauge to verify the actual pressure you do have.
     
  10. grindkings

    grindkings 1/2 ton status

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    Sending unit.?
     

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