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Discussion Starter #1
I have been concerened with the oil pressure reading on the dash gauge since about a few weeks ago. Short story is, i was driving on the highway, noticed a shuttering sound then a tick and tapping sound coming from the engine. I pulled over, the engine was full of oil but i noticed the oil gauge on the dash was reading low. Normally it reads 40+ all of the time. It was lower than 40 almost to 20 PSI. I connected a mechanical oil gauge to the engine and here are the results:

At cold start the mechanical gauge reads 44-45 PSI then after about 1:30 goes down to 41 PSI at idle. Here is a video of cold start to idle:

After the engine is up to operating temp and has been running for 15-20 minutes, the mechanical gauge reads 28 PSI and the gauge on the instrument panel reads in between 20-25 PSI at idle. Here is a video of the engine warmed up and running for about 15-20 mins

Then I turned on the Air Conditioner. When the compressor came on the mechanical gauge started fluctuating as well as the instrument panel gauge. The panel gauge read a little below 20 and the mechanical gauge fluctuated between 25-28 PSI. When i turned the AC off, the mechanical gauge did not fluctuate any longer. Here is a video after the AC was turned on:

The parts that have been replaced so far are:
New oil pick up tube
New oil pick up tube 0-ring
New oil pressure sensor

Using Mobil-1 5W-30 and a Wix oil filter.

By watching these videos, would you say i need a new oil pump?
 

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Your over thinking this, the pressures are well within specs.

The bouncing needle might concern me, but it's only 3 lbs; and if it only happens with AC on, I'd suspect changes in engine speed are changing the pump speed which impacts the pumps output.
 

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Discussion Starter #3
I’m concerned because the dash gauge used to show above 40 all of the time before the one time it started shuttering and ticking/tapping and the needle on the dash was always steady. Now the dash gauge fluctuates a lot at idle and while driving. It didn’t do that before.

Since the oil pick up tube ring and pressure sensor didn’t help it go back to what I would call normal, I’m concerned that the pressure relief spring/valve is stuck open in the oil pump. This is why I’m considering replacing the oil pump with a Melling M295HV.

the oil pressure drops from 40 to the 20’s on the dash gauge which was not normal before. The engine has 146k on it. I don’t want to be on a long trip and have the engine start tapping at highway speeds again.

also I didn’t find any antifreeze in the oil or any metal flakes or sludge when I pulled the oil pan.

the truck has 4.10 rear end gears so when driving on the highway, the engine runs above 2k rpms. Don’t want to starve the engine of oil if it can’t build up pressure.
 

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this issue you have is most common a crankshaft bearing wear . cold start oil pressure is normal then as you drive it and the engine heats up the oil pressure drops and the engine makes noise. oil viscosity drops as it heats up and the crank bearings have more wear and the oil pressure drops. I would do a oil test lab see if what metals are in the oil.
when did you buy it ? was this a tow truck load work truck ? probably need a new engine ..
 

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this issue you have is most common a crankshaft bearing wear . cold start oil pressure is normal then as you drive it and the engine heats up the oil pressure drops and the engine makes noise. oil viscosity drops as it heats up and the crank bearings have more wear and the oil pressure drops. I would do a oil test lab see if what metals are in the oil.
when did you buy it ? was this a tow truck load work truck ? probably need a new engine ..
I have had the truck for about 5 years now. Hasn’t given me trouble until now. I bought it used. It was a company truck for a sales person. The truck had 120k on it when I bought it and looked/ran like it was taken care of. Probably received fleet maintenance.
The engine right now is not making a ticking or tapping noise. Even when the engine is warm and the dash oil gauge reads 20-25 psi I still don’t hear ticking or tapping.

It only made the ticking and tapping sound the one time I was driving it on the highway. That’s when the oil pressure started reading low on the dash gauge. It was all of the sudden when it happened.

would crankshaft bearings go out all of the sudden? Or would it be a gradual wear?
When I dropped the oil pan, I did not see any metal flakes in the oil or in the bottom of the pan. There was hardly any sludge in the bottom of the pan. I didn’t take the Windage plate off the bottom of the motor because every thing else looked normal.
 

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I have been concerened with the oil pressure reading on the dash gauge since about a few weeks ago. Short story is, i was driving on the highway, noticed a shuttering sound then a tick and tapping sound coming from the engine. I pulled over, the engine was full of oil but i noticed the oil gauge on the dash was reading low. Normally it reads 40+ all of the time. It was lower than 40 almost to 20 PSI. I connected a mechanical oil gauge to the engine and here are the results:

At cold start the mechanical gauge reads 44-45 PSI then after about 1:30 goes down to 41 PSI at idle. Here is a video of cold start to idle:

After the engine is up to operating temp and has been running for 15-20 minutes, the mechanical gauge reads 28 PSI and the gauge on the instrument panel reads in between 20-25 PSI at idle. Here is a video of the engine warmed up and running for about 15-20 mins

Then I turned on the Air Conditioner. When the compressor came on the mechanical gauge started fluctuating as well as the instrument panel gauge. The panel gauge read a little below 20 and the mechanical gauge fluctuated between 25-28 PSI. When i turned the AC off, the mechanical gauge did not fluctuate any longer. Here is a video after the AC was turned on:

The parts that have been replaced so far are:
New oil pick up tube
New oil pick up tube 0-ring
New oil pressure sensor

Using Mobil-1 5W-30 and a Wix oil filter.

By watching these videos, would you say i need a new oil pump?
Think I can help here... there’s a guy I watch on YouTube, his 04 z71 had the exact same issue. (praying my 06 z71 has plenty of miles left until it has the same problem)😬... Anyways, it’s most likely going to be your crankshaft bearings that are going out, BEFORE getting that worked on just change out the oil pump with the Melling one on Amazon, it’s like $55? Maybe a $500 job in labor just because so much has to be removed to get access to the timing chain cover that needs to be removed... If that doesn’t do the trick then it’s most likely those bearings, which is a costly job, but if you love your cat eyed like I do then it’s worth it, mine as well get a full internal part swap done while you’re at it and they’re digging around in the block, just saying. I’ll shoot a link to his video when I can find it. Best of luck! Let us know how it goes, I’ll be curious to find out.
 

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I have been concerened with the oil pressure reading on the dash gauge since about a few weeks ago. Short story is, i was driving on the highway, noticed a shuttering sound then a tick and tapping sound coming from the engine. I pulled over, the engine was full of oil but i noticed the oil gauge on the dash was reading low. Normally it reads 40+ all of the time. It was lower than 40 almost to 20 PSI. I connected a mechanical oil gauge to the engine and here are the results:

At cold start the mechanical gauge reads 44-45 PSI then after about 1:30 goes down to 41 PSI at idle. Here is a video of cold start to idle:

After the engine is up to operating temp and has been running for 15-20 minutes, the mechanical gauge reads 28 PSI and the gauge on the instrument panel reads in between 20-25 PSI at idle. Here is a video of the engine warmed up and running for about 15-20 mins

Then I turned on the Air Conditioner. When the compressor came on the mechanical gauge started fluctuating as well as the instrument panel gauge. The panel gauge read a little below 20 and the mechanical gauge fluctuated between 25-28 PSI. When i turned the AC off, the mechanical gauge did not fluctuate any longer. Here is a video after the AC was turned on:

The parts that have been replaced so far are:
New oil pick up tube
New oil pick up tube 0-ring
New oil pressure sensor

Using Mobil-1 5W-30 and a Wix oil filter.

By watching these videos, would you say i need a new oil pump?
Here’s the video below... watch the whole thing. He was having the same issue you’re having. Again, do the oil pump first as it’s a $600 job, if needed get your cam and internals swapped out, might run you $2-3K but you’ll be good for a while after you do if you intend to keep your z71.

 

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Brenden not finding fault with your diagnosis; but just an FYI, 25 psi is not an indication of worn bearings. As I said in an earlier post, 25 psi is within the GM specs.

Every once in awhile a small piece of dirt gets stuck in a lifter and the lifter will rattle until the dirt breaks free, at which time, the lifter becomes quiet again.

The computer will tell you if the pressure falls into dangerous territory, if that happens, the pressure will be 5 psi, or less.
 

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My 2001 5.3L Suburban with 285k miles oil pressure at operating temperature at idle is 40psi.
At 2000 rpm, oil pressure is 60 psi.

25 psi oil pressure at idle is still ok but on the low end and is an indication the bearing clearances are getting loose.
You should plan on a rebuild if you plan to keep it.
 

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I have had the truck for about 5 years now. Hasn’t given me trouble until now. I bought it used. It was a company truck for a sales person. The truck had 120k on it when I bought it and looked/ran like it was taken care of. Probably received fleet maintenance.
 

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Discussion Starter #13
I ordered a Melling M295HV oil pump and all the gaskets and a timing chain to go with it. I'm planning on pulling the oil pan again and replacing the oil pump. I hope its not crank shaft bearings! When I pulled the oil pan the first time to replace the oil pick up tube o-ring, there was a minimal amount of sludge in the bottom of the pan and I did not find any metal shavings or flakes. The minimal amount of sludge shows me that the oil was maintained on a regular basis. I have no reason to believe that the truck was abused or neglected when I bought it, hence why I bought it.

I'm hoping that it is just the relieve valve stuck or sticking in the oil pump and the new HV oil pump will correct that and help the lower oil pressure.

I would expect this oil pressure crap out of a Ford but not a Chevy......especially at 150K miles. The previous truck I had was a F150 with the nightmare 5.4L engine in it. Talk about oil pressure and timing issues.
 

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Ok, with just 150k miles, I don't think it's the crankshaft bearings.
New oil pump and oil pressure relief valve sounds like a good plan.
Relief valve springs could have gone weak or broken.
 

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I do the oil changes .. I take 45min with the engine hot drain all the oil out. then I use mobil synthetic dexos GM approved engine oil . my 2000 5.3L engine oil pressure is 40-60 PSI.. cold 60 then it drops to 43psi at idle when hot.
some do have sludge when conventional oils used .. because we today have to use alcohol gasoline the engine oil creates sludge because of water in the gasoline ...
my 2000 truck I had engine knocks when new .. then I used Mobil synthetic @10K miles on my new truck .. no engine knock on a cold start .. and the oil pressure did not go to 80psi .. only went to 60psi when cold.. oil flowed faster better flow on the synthetic.
the previous oil change I did I messed up .. I check my oil every 30 days .. oil level was at the full mark.. well I was thinking when did I change the oil ??? looked up the maintenance book and I did it 11K miles ...ago.. only used 1/8qt oil....normally the engine uses 1/3-1/2 qt every 7K miles..
I also use purolator pure one filters ... made in USA.. no engine work just replaced the spark plugs ..
 

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Discussion Starter #16
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these are photos with the bottom oil pan off. I filtered the oil when I drained it. Found no metal flakes. Found no metal flakes when I removed the pan and windage tray.

I don’t see any thing out of the ordinary for a 150k mile engine. From the little I can see, I didn’t see any unusual scoring of the camshaft or the cylinder walls....but I’m not an engine expert.


thoughts? Any thing look unusual from the bottom side?
 

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Looks like a good wear pattern on the camshaft lifters - no worries there. Bottom end looks clean as well. Can't tell what kind of wear on the crank without bearing cap removal. Crank and cam bearings clearances determine oil pressure unless its got an opening/leak somewhere in the oil circuit.
 

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Well either I did something wrong or there is something else wrong....

This is with a new MH295HV oil pump and a new timing chain. Idle with the engine at normal operating temp 25-30 psi. 1K rpm and more is above 40 psi. So better oil pressure with normal driving. However the mechanical gauge is bouncing like crazy all of the time now. Dash gauge is still moving a lot more than “normal”.

I don’t hear anything that sounds abnormal. I can’t figure out why the mechanical gauge is bouncing like crazy. All the parts were torqued correctly and the timing is correct. The engine runs smooth. Any ideas on why the mechanical gauge is bouncing like crazy?

After M295HV oil pump install
 

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It bounced in your opening post when you turned on the AC.
Bouncing pressure is usually a pumping irregularity.
But, you've recorded 2 pumps doing the same thing.
The only other thing is cavitation, could you be over filling the crankcase?
 

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I remove the oil filter and cut off the cover to inspect the filter media...no metal particles on the pan bottom with 150K miles that is weird .... there should be some metal debris ..
installing the new pump it will pump more oil .. then the pressure rises more than the old pump.
my 5.3L at normal operating temp at idle pressure is 38-42PSI.. @2K rpm 50psi ..
I use pure one purolator oil filters .. made in USA and the media is very strong and larger than most filters .. more flow better filtration ..

oil pressure at your new pump all is good..
 
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