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Discussion Starter · #1 ·
I have a consistent issue with my 2004 Trailblazer where the oil pressure will slowly drop from 50-60 psi all the way down to 0. Like I said, this happens consistently and it takes around 10 minutes or so for the oil pressure to drop down to 0 when it is hot. When it is cold it takes around 15 minutes for it to drop to 0. Those times probably aren’t the most accurate, I don’t exactly time how long it takes for it to drop. What is having me stumped though is the fact that after shutting the car off for even just a second and then turning it back on the pressure will rise right back up to 50 psi but begin to drop again. After turning it back on more throttle will make the pressure go higher, but as it slowly drops throttle begins to make no difference in the pressure. As a matter in fact, it almost seems to make it drop quicker. I know that all of these pressure readings are indeed correct though because I put in a mechanical pressure gauge so I am not relying on the one in the dash (because it is simply just a switch). Does anyone know what this problem is caused by????? I don’t want to immediately blame the oil pump or the o-ring on the pickup tube because if either of those were bad, the car should NOT re-gain all of its oil pressure, let alone within seconds.
 

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Discussion Starter · #2 ·
I would also like to clarify, after I turn the car off and turn it back on each time, it will quickly rise to 50 psi (like it should) and then it will take around 10 minutes for it to drop all the way to 0. And I also forgot to mention, I added a quart of Oil Honey to the engine yesterday and that seemed to help it significantly. I would only be able to make it a few miles before having to turn the car off and on each time, but now like I said I can make it significantly further.
 

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Discussion Starter · #4 ·
Could be a clogged oil pickup, the o ring on the pump pick up failed, or there's too much clearance on the engine bearings.
Are there any engine noises?
If it's a clogged oil pump pickup, you may be able to use B&G to clean it out, along with a few oil changes to clean out the B&G.
Since you said Oil Honey improved the situation (thickened the oil), I suspect the problem is the engine bearings themselves.
Thank you for the reply! I had originally thought that the problem was occurring because of a clog, but if it was simply a clog I would think that I wouldn’t regain oil pressure so fast when I start it back up. I’ve also been running a bit of SeaFoam in the oil to try and clear up any sludge that may be stuck in places. And I’ve considered the main bearings as well, but if the bearings were my problem I would highly doubt that my oil pressure would come back, especially right back up to 50 psi. If I had to guess, I will likely end up pulling the oil pan to replace the pickup tube and bearings if they appear to be bad. I will also probably end up replacing the pump, but I just wanted to ask out here in case the issue is caused by something that isn’t the pump because it’s an SOB to pull the pump and pickup tube.
 

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Discussion Starter · #5 ·
Thank you for the reply! I had originally thought that the problem was occurring because of a clog, but if it was simply a clog I would think that I wouldn’t regain oil pressure so fast when I start it back up. I’ve also been running a bit of SeaFoam in the oil to try and clear up any sludge that may be stuck in places. And I’ve considered the main bearings as well, but if the bearings were my problem I would highly doubt that my oil pressure would come back, especially right back up to 50 psi. If I had to guess, I will likely end up pulling the oil pan to replace the pickup tube and bearings if they appear to be bad. I will also probably end up replacing the pump, but I just wanted to ask out here in case the issue is caused by something that isn’t the pump because it’s an SOB to pull the pump and pickup tube.
I would also like to take the time to mention my current suspicions for what the issue actually is. This would also be a good time to mention that there is a problem with my cam actuator (it’ll make sense later). Because the car regains nearly all of its oil pressure when I turn off and restart the car, it almost acts like something electronic is slowly opening up inside of the engine causing me to slowly lose pressure.I have also plugged in a computer to the car to read data, but what it is telling me is that the car wants about 24 degrees of timing or so out of the engine while I’m driving, but the cam actuator will only give me 2 to 3 degrees of timing. My thinking is that if the camshaft is not being timed correctly, the hydraulic lifters have to push extra far or extra hard to keep the clearance right in the valvetrain. Because they are taking extra pressure, the pump can’t keep up with the amount of pressure the lifters need causing my slow drop of oil pressure. That would also explain why it would go right back up as the cam is resetting its timing when I turn the car off and back on. It’s just a theory, but that’s my current guess.
 

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Discussion Starter · #8 ·
......... and quit hearing Zebra hoofbeats --- they're really just horses ---

................. so keep the "diagnostic" gymnastics to a minimum and concentrate on "cause and effect" here ---

BELIEVE the gauge until you can prove it's wrong.
To answer your question, it’s the 4.2 liter engine. I did not specify the engine it is because I thought I put this forum in the 4.2 engine section.

Secondly, I never once didn’t trust my mechanical gauge. I simply don’t trust the stock gauge because it is literally just a switch. It will read 40 psi or 0.

Lastly, hopefully this format works for you a little better. But I must note that the diagnostic “gymnastics” are there because I’m trying to find the answer to a VERY specific problem. And when I problem solve, it is very very helpful to have as much detail as possible, especially when fixing a problem as specific as this.

Here’s your cause and effect: Cause = I don’t know, that’s what I’m trying to figure out. Effect = Oil pressure that slowly drops to 0, but comes back up to 50 when I turn the car off and back on.
 

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Discussion Starter · #10 ·
KollinKnack06, until Ravalli responds, I would like to toss this bit of information regarding the 4.2L engine and oil pressure. The 4.2L engine was designed with the volume of oil moved in some unit of time instead of oil pressure. Thus, a low oil pressure reading (above 0 psi) is considered normal. This may be unsettling to many as we've had it drilled into us for a long time that oil pressure must be in the double digits or else there is something wrong.

Well, oil pressures below 10 psi are normal for the 4.2 L engine as long as the volume of oil moved is correct.
That is very interesting! Thank you for the information.

I knew that the oil pressure on that engine could be as low as 8 psi, but not 0. I suppose then how would I know if I’m not moving the correct volume of oil?

I should also note that although this had only happened once, and it hasn’t happened since, I did hear what I believe to be lifter clatter.
 

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Discussion Starter · #21 ·
Thank you to everyone who has responded! That oil pressure switch screen could make sense, but I have a mechanical gauge that is coming right off the secondary plug in the oil filter block. Unless that screen is deep enough to block both ports, that should not be my issue.

I should also note that although it only happened one time, I believe I did hear lifter clatter, which makes me believe that I am indeed losing oil pressure. What I can’t understand is why it comes back after I turn the car off and back on.

And btw, thanks to y’all for noting the mono paragraph bullshit. You must be pretty lazy if you can’t break apart a damn paragraph while you read it.
 
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