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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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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.
 

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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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'05 Chevy TB EXT
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Crap! Monoparagraphs again .......

What engine is this?

The 5.3LS engine has tons of oil pressure problems --- and they are real in spite of your furtive wishes..

If you REALLY have an oil pressure problem in a 5.3LS --- then do not drive it until you fix it.

From this point on --- I will NOT read a monoparagraph ... break your thoughts up like I have done here or I'm outa here!

I mean it.
 

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'05 Chevy TB EXT
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......... 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.
 

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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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2004 chevy trailblazer_lt
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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.
 
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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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Unfortunately, I do not know how low it can go without there being any oil flow. Also, I do not know what the oil flow specification is. Two very good questions that I do not know if they have been researched.

Only time I've heard any clattering in the lifters on my 04 TrailBlazer was after an oil change when I took a long break before putting oil back in (I left the hood up and the 7 quarts of oil on the engine cover and the battery).
 
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I have just recently fix this problem in my 5.3L Envoy, the Oil pressure sensor failed and the screen was clogged, I was driving and all of the sudden oil pressure dropped to zero, I shut the engine down checked the oil and oil was fine, started it back up and oil pressure was present, when I took off the oil pressure went back to zero, I was 2 block from home, made it home, did some research and started with the cheapest fix, problem solved, I am not sure if the sensor is bad but if you are going to change the sensor change the filter screen as well this is a must, the parts are in stock at most auto dummy's for under $60 (filter screen & sensor) my cousin has the 4.6L Envoy and he had the same problem, removed and replaced sensor and filter screen and problem solved, start with cheapest fix first, you wont see the filter screen unless you have an inspection mirror and a flashlight, take an automotive pick, looks like a dental pick to remove filter screen located in the sensor port, don't worry about puncturing the screen, throw it out and replace with new, it's only a $7-$9 part, you can buy just sensor or sensor screen separately, usually it's the screen but why go through the hassel again if the sensor ended up being bad, I would buy the kit with both parts, I bought an extra screen just because, you can litteraly change these out on the fly if need be.
 

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'05 Chevy TB EXT
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I have just recently fix this problem in my 5.3L Envoy, the Oil pressure sensor failed and the screen was clogged, I was driving and all of the sudden oil pressure dropped to zero, I shut the engine down checked the oil and oil was fine, started it back up and oil pressure was present, when I took off the oil pressure went back to zero, I was 2 block from home, made it home, did some research and started with the cheapest fix, problem solved, I am not sure if the sensor is bad but if you are going to change the sensor change the filter screen as well this is a must, the parts are in stock at most auto dummy's for under $60 (filter screen & sensor) my cousin has the 4.6L Envoy and he had the same problem, removed and replaced sensor and filter screen and problem solved, start with cheapest fix first, you wont see the filter screen unless you have an inspection mirror and a flashlight, take an automotive pick, looks like a dental pick to remove filter screen located in the sensor port, don't worry about puncturing the screen, throw it out and replace with new, it's only a $7-$9 part, you can buy just sensor or sensor screen separately, usually it's the screen but why go through the hassel again if the sensor ended up being bad, I would buy the kit with both parts, I bought an extra screen just because, you can litteraly change these out on the fly if need be.
That screen is indeed a problem ----- it can cause the sender to not "see" pressure because the screen is plugged up.

But --- if that's so --- and there's something that is clogging up the screen --- you've got other problems anyway.

Besides ... this is about a 4.2L engine ... so what I just said doesn't apply to the 4.2L.

And PLEASE --- no more monoparagraphs.

See my answer?
Pose your statements in approximately the same format so people will actually WANT to help you --- we're all volunteers here and I for one, refuse to do this very much --- if I have to pick paragraphs apart to see what the trouble is ... OK?​
 

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That screen is indeed a problem ----- it can cause the sender to not "see" pressure because the screen is plugged up.

But --- if that's so --- and there's something that is clogging up the screen --- you've got other problems anyway.

Besides ... this is about a 4.2L engine ... so what I just said doesn't apply to the 4.2L.

And PLEASE --- no more monoparagraphs.

See my answer?
Pose your statements in approximately the same format so people will actually WANT to help you --- we're all volunteers here and I for one, refuse to do this very much --- if I have to pick paragraphs apart to see what the trouble is ... OK?​

That's not what that means, have you ever heard of carbon buildup ?
All engines eventually have it, most likely there is carbon particles built up in older engines.

As far as monopharagraphs RAV

This answer wasn't for you in the first place it was for KollinKnack06, because he's not a lazy ass and knows how to read monopharagraphs.

That's a problem with people today.

Too lazy to do anything along with their self entitlement, if you know what commas are ? They sepparate/pause the sentence as I have demonstrated for you, if you have a problem reading monopharagraphs then YOU are the problem.

It doesn't matter whether it's the 5.3 or the 4.2, All GM products all have oil sensors with filter screens, they all work in the same way and have the same type of problems which can be fixed the same way.

This is not a grammar lesson Mr. Professor, apparently he didn't have a problem with the way I wrote correcting me as you did, he was looking for an answer, I been around the block a few decades and this isn't my first rodeo.

I hope this helps your Kindergarten mentality RAV by spacing my sentences in a retarded way just for you.

No....You're right lets write this out in the dumbest way possible because it's easier for you.

Now you can kindly piss off!!
 

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2004 chevy trailblazer_lt
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RED05ED, just one point of clarification. Not ALL GM products have oil pressure sensors/switches have filter screens. The 99 Silverado with a 5.3 L engine I used to own did not have a filter screen for the oil pressure sensor/switch, and nor do the 1992 Oldsmobile 88 and 1999 Buick Century engines have filter screens for their oil pressure sensors/switches.

Also, there are plenty of us on here who do appreciate it when people take an extra moment or two to think about grammar and those who will be reading their postings.
 

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2004 chevy trailblazer_lt
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Trust me, we are far from being millennials and kindergartners...
 
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Trust me, we are far from being millennials and kindergartners...

I wasn't meaning anything to you chem_man you seem alright and legit, but you know what they say about first impressions, and apparently I did not read the fine print in the rules and regulations about mono pharagraphing of ravallis rules, and btw rav the 5.3 is not an actual LS is is merely a platform of the LS, Good Day Sir!!
 

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2004 chevy trailblazer_lt
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Trust me when I say that Ravalli Surfer, despite his sometimes good natured exterior, is an extremely knowledgeable automotive professional technician/mechanic, who is one of the best automotive diagnosticians I have run across, and I used to work with one many years ago in Indianapolis. This forum is darn lucky to have him.
 
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