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Sudden loss of oil pressure - potential causes?

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Old 07-19-2010, 12:09 PM   #1
Stuttgart951
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Default Sudden loss of oil pressure - potential causes?

Actual loss of (engine) pressure - not a gauge failure.

Warning light lit after approximately 20 minutes of normal operation this morning. Pressure gauge fluctuated between 1-2.

Killed engine immediately and coasted to stop. Temperature normal (not above 194 degrees - 2nd mark). 2-second re-fire after 3-4 minutes confirmed lack of oil pressure (audible).

No physical loss of oil evident; no drips, drops, puddles or smell of same burning.

Suspect failure of/in circulation system. All oil appears to be in reservoir/cooler.

Oil changed in shop 3 days ago along with all belts (alternator, AC, etc). Passed tech inspection.

Search brought up multiple threads. However, most pertain to sender/gauge/electrical failures.

Given the lack of physical oil loss or any smoke, blockage in return tube is first thought. Lines? Pump? Relief pistons/springs?

Other ideas? Has to be something minor or the car would be sitting in a puddle. What may not have been properly refastened/re-connected/etc during the oil change?

Thanks.
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Old 07-19-2010, 12:50 PM   #2
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First thing that comes to mind is the thermostat/spring assembly that resides in the bottom of the reservoir: when the spring fatigues in 928's ( same assembly pn's), there is a loss of oil pressure ... in 993's, it leads to overheating of the oil .... but may also lead to pressure loss - all depends on where the slider valve/plug is stuck in its bore.

When some wrenches drain the case, it is possible to loosen the wrong "drain plug" .... the wrong one being a spring loaded check valve to control oil over pressure: without it functioning correctly, doubt that there would be much oil pressure apparent ...


Anyway, there are two of the cheaper situations to check out ... save the $$$$ ones in case this info doesn't apply
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Old 07-19-2010, 12:55 PM   #3
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JMHO, but the very first thing you should do is open the oil filters and see if there is any metal in the folds of the paper pleating.

Use a proper filter cutter, not a saw otherwise you won't learn anything.
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Old 07-19-2010, 12:57 PM   #4
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I agree with Garth 100%...sounds like the pressure spring might have broken. Its a quick check to see if its so. You also had good pressure initially, that sounds like a failure rather than something that was there from day one.

Even if the filter was plugged (due to a manufacturing defect or something similar), the filter is on the return side, so I think you should not lose pressure (not totally sure about this since I have never had a plugged filters).

I would go under the car and pull the pressure relieve valve and check the springs. Make sure there are no missing pieces if its broken, that could be "bad".

Cheers,

MIke
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Old 07-19-2010, 03:05 PM   #5
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Quote:
Originally Posted by Steve Weiner-Rennsport Systems View Post
JMHO, but the very first thing you should do is open the oil filters and see if there is any metal in the folds of the paper pleating.

Use a proper filter cutter, not a saw otherwise you won't learn anything.
+1 on good advice ..... BTW, even if one doesn't have 3" od pipe cutters, a fine hacksaw blade used near the top rim can still do a job if one is careful: the filter can is ferromagnetic, so any particles from it will jump to a magnet - generally, the chips & dust from bearings, etc that one doesn't want to see in the pleats are Al, Mg, Cu, etc ... non-magnetic bits
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Old 07-19-2010, 03:47 PM   #6
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Ok - good stuff, thanks.

Just returned to office after meeting tow truck. Car is onits way back to the shop - will mention the above possibilities.

Have already instructed them to cut open filter and look for shavings.

Suppose I'm just glad I happened to be visually checking my speed at the exact instant the pressure dropped out of the corner of my eye.

Will update with results of shop's assessment.

Thanks again.
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Old 07-19-2010, 07:00 PM   #7
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EDIT: Should also mention that oil weight was not changed. Mobile 1 15w50 as per the norm.

Last edited by Stuttgart951; 07-20-2010 at 03:57 PM.
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Old 07-20-2010, 03:58 PM   #8
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Valve/spring is fine. Crankcase has oil. Nothing unusual found. No metal shavings.

Still no pressure.

Stumped. Investigation ongoing...
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Old 07-20-2010, 04:09 PM   #9
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Sorry to ask the obvious but how do you know its not a gauge failure? Have you tested the OP?
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Old 07-20-2010, 04:21 PM   #10
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Quote:
Originally Posted by ppashley View Post
Sorry to ask the obvious but how do you know its not a gauge failure? Have you tested the OP?
Good question. He did say it was audible so does that mean rattling or ??? There must be a way of verifying that the gauge is indeed functional. If it is functional then running the engine with a temporary mechanical gauge would be out of the question.
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Old 07-20-2010, 05:00 PM   #11
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Gauge functions properly - oil is not getting to the engine.

What needs to be removed to get at the oil pump? Have factory manual at home... currently at office.
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Old 07-20-2010, 05:32 PM   #12
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Quote:
Originally Posted by Stuttgart951 View Post
Gauge functions properly - oil is not getting to the engine.

What needs to be removed to get at the oil pump? Have factory manual at home... currently at office.
Oil pump is inside the case and is VERY inaccessible. Basically the labor to access the oil pump launches you right down the slope to an engine rebuild. With the elimination of the sump plate many years ago, I'm not sure you can even see the oil pump or intermediate shaft that drives it without removing the cylinders.
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Old 07-20-2010, 05:40 PM   #13
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If it is determined that oil has not been circulating the engine should be coming out regardless (unfortunately).
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Old 07-20-2010, 05:41 PM   #14
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I don't like the direction this thread is headed. The oil pressure failure happened immediately after an oil change, so clearly the shop caused a problem. There's absolutely no way a properly-done oil change can cause this kind of failure. No way. Period.

I still think Garth was right, that they accidentally pulled the pressure relief parts (happens all the time!) and botched something there. They clearly did *something* wrong.

My worry is that by giving them the car back, you'll never learn the truth but instead get stuck with a $7,000 engine repair bill.
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Old 07-20-2010, 05:54 PM   #15
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p.s. oh and here's one possible mistake: if they unhooked the oil return line to gain access to the small oil filter, maybe they stuffed a rag inside the tube so it didn't leak all over them. Then somehow forgot to remove it when re-attaching the oil line.

Hey, it's a longshot but again, there aren't too many ways they could have caused this problem.
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Old 07-20-2010, 05:54 PM
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