low oil pressure
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Northstar Engines and System Technical Discussion Discussion, low oil pressure in Cadillac Engine Technical Discussion; 96 sts. 121k miles. oil line came off at idle last year. low oil pressure message. towed home. fixed. today ...
  1. #1
    stoveguyy is offline Cadillac Owners Connoisseur
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    low oil pressure

    96 sts. 121k miles. oil line came off at idle last year. low oil pressure message. towed home. fixed. today i got a oil indicator light on dash but no message. drove to store. came out, got low oil pressure message. no leaks this time. towed home. next step? mechanical pressure gauge? did headgaskets 2 yrs ago. 10k miles since. balancer bolt is tight. worth checking again?

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    tateos's Avatar
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    Re: low oil pressure

    Oil level first, then change oil pressure sending unit - fairly easy and costs less than $10. Balancer bolt? I guess...if you didn't tighten it properly 10K ago...but not if you did it right in the first place

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    stoveguyy is offline Cadillac Owners Connoisseur
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    Re: low oil pressure

    success. i read about the pressure relief valve and overfilling the crankcase with extra oil. tried reving to 3500 and nothing changed. than blipped the throttle several times and dang if the light went off. the valve train rattle went away and the motor quieted down. yes, 15-17quarts of oil really takes awhile to drain out.

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    32vmonte is offline Cadillac Owners Member
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    Re: low oil pressure

    Quote Originally Posted by stoveguyy View Post
    success. i read about the pressure relief valve and overfilling the crankcase with extra oil. tried reving to 3500 and nothing changed. than blipped the throttle several times and dang if the light went off. the valve train rattle went away and the motor quieted down. yes, 15-17quarts of oil really takes awhile to drain out.
    Wait so how did that much oil get in the car in the first place? Your pistons had to be bathing in oil if not running into it.

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    Re: low oil pressure

    He purposely overfilled it: The GM procedure for priming a Northstar oil pump (which sits higher than the normal oil level) if the oil pump pickup anti-drainback ball check has a chip lodged in it and so "loses prime". One time is usually sufficient to dislodge the offending chip.

  7. #6
    stoveguyy is offline Cadillac Owners Connoisseur
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    Re: low oil pressure

    the overfill method works for priming the oil pump and fixing the pressure relief valve issue. i am not clear if the caddy prv function is to route oil to the bearings on startup and than when the pressure builds to open and send it to the oil cooler? that is the way is works on some porsche motors. you would have to get into a discussion of oil pump design to get more details.

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    Re: low oil pressure

    The heads definitely seem to be the last in the cycle

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    Re: low oil pressure

    In the Northstar system the oil pressure relief valve (a ball/spring or plunger/spring) ports excess cold oil, and therefore pressure, from the discharge side of the pump directly back to the intake side of the pump. That system is set to relieve oil pressures above about 60 psi in GM engines. (Oil flow and volume is the primary concern in engine lubrication, not necessarily pressure.)

    The anti-drainback ball check prevents oil in the pump and galleries from siphoning back into the pan when the engine is off: the pump itself is higher than, rather than immersed in, the oil level in the pan as is more common in other engines. So, because a gerotor pump is not self-priming, you must get oil into the pump by "flooding" it. As soon as you get pressure shut down and drain the oil back to the proper level.

    In those FWD Northstar drivetrains equipped with an oil cooler (not all installations have a cooler) I believe the cooler bypass is either a pressure spring valve or thermostatic. Not sure which, but it's a bypass, not a pressure relief. For simplicity I would guess that it is dependent on pressure (cold oil is "thicker"), so it would be an internal arrangement similar to the pump discharge pressure relief: spring loaded, and therefore the amount of oil sent to the cooler is also roughly oil temperature dependent.

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    stoveguyy is offline Cadillac Owners Connoisseur
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    Re: low oil pressure

    the TSB states to verify the valve train clatter has diminished/stopped as a sign the oil pressure has returned to normal. i can vouch for that. i had the car towed since i did not feel right driving with what i thought was low oil pressure. i assume i had almost none and did not want to put a load on the motor by driving it. would that be a good assumption? anyone here think its ok to drive a car with low oil pressure?

  11. #10
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    Re: low oil pressure

    If the engine is now mechanically quiet with no oil pressure light at hot idle and runs with good throttle response, you're OK. Watch the oil level every week for the next month, two weeks thereafter. Keep the level as posted, halfway up the dipstick hashmark, with your favorite oil in the viscosity range recommended for your engine.

    If you really get antsy later this Fall, bum a mechanical oil pressure gauge from a wrencher friend and temporarily plumb it, using a pipe T in order to keep the electrical sensor also, to the sending unit port on the oil filter adapter. Run the capillary tubing and duct tape the gauge to the lower windshield area in front of the dash panel and watch the pressure for a week or so under different running conditions. That is the only way to learn what pressures your engine runs.

  12. #11
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    Re: low oil pressure

    Low oil pressure and no oil pressure are two different things. According to post #3 you had NO oil pressure. You did the right thing.

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    Re: low oil pressure

    Quote Originally Posted by submariner409 View Post
    In the Northstar system the oil pressure relief valve (a ball/spring or plunger/spring) ports excess cold oil, and therefore pressure, from the discharge side of the pump directly back to the intake side of the pump. That system is set to relieve oil pressures above about 60 psi in GM engines. (Oil flow and volume is the primary concern in engine lubrication, not necessarily pressure.)

    The anti-drainback ball check prevents oil in the pump and galleries from siphoning back into the pan when the engine is off: the pump itself is higher than, rather than immersed in, the oil level in the pan as is more common in other engines. So, because a gerotor pump is not self-priming, you must get oil into the pump by "flooding" it. As soon as you get pressure shut down and drain the oil back to the proper level.

    In those FWD Northstar drivetrains equipped with an oil cooler (not all installations have a cooler) I believe the cooler bypass is either a pressure spring valve or thermostatic. Not sure which, but it's a bypass, not a pressure relief. For simplicity I would guess that it is dependent on pressure (cold oil is "thicker"), so it would be an internal arrangement similar to the pump discharge pressure relief: spring loaded, and therefore the amount of oil sent to the cooler is also roughly oil temperature dependent.
    Good one, Sub

  14. #13
    aac123 is offline Cadillac Owners Member
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    Re: low oil pressure

    Low or No Oil Pressure
    The following can cause low or no oil pressure:

    * Low oil level-fill to the full mark on the oil level indicator.
    * Slow idle speed
    * Incorrect or malfunctioning oil pressure switch-replace the oil pressure switch.
    * Incorrect or malfunctioning oil pressure gauge-replace the oil pressure gauge.
    * Improper oil viscosity or diluted oil
    * Install oil of proper viscosity for expected temperature.
    * Install new oil if it is diluted.
    * The oil pump is worn or dirty-clean or replace the oil pump.
    * The oil filter is plugged-replace the oil filter.
    * The oil pickup screen is loose or plugged
    * replace the oil pickup screen.
    * A hole in the oil pickup tube-replace the oil pickup tube.
    * Excessive bearing clearance-replace the bearings.
    * Cracked, porous, or plugged oil galleries-repair or replace the engine block.
    * The gallery plugs are missing or improperly installed-install or repair as necessary.
    * The pressure regulator valve is stuck.
    * Check the pressure regulator valve for sticking in the bore.
    * Check the bore for scoring and burrs.
    * The camshaft is worn or poorly machined-replace the camshaft.
    * Worn valve guides-repair as needed.

  15. #14
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    Re: low oil pressure

    Pretty comprehensive, BUT: valve guides are lubricated only by vapor and what tiny amount of oil works its way down the stem from the seal. There is no connection from the lubrication passages to the valve guides. Excessively worn guides will definitely increase oil consumption, not decrease pressure.

    The hydraulic cam followers or static lash adjusters are fed by pressure oil for that is what supplies the hydraulic "cushion" in the valve train.

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