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Discussion Starter · #1 ·
My truck has been sitting for theast week at the body shop. I dropped it off with it never having any issues. It's a 2008 sierra with a 5.3. After picking my truck up and leaving the body shop, it suddenly lost oil pressure once it got to normal running temp. I pulled over and checked the oil and it's fine. I towed the truck back to my buddies house and let it sit and cool off. Cranked it back up and once it got to running temp the pressure dropped again and the oil light came on. There's no unusual sounds coming from the motor or anything. Any ideas on what could be going on?
 

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When your oil is cold its much thicker compared to when its hot, thus hot oil building less oil pressure.

Also, your ECM is commanding an idle that is a few hundred rpm higher than it commands once teh engin is warm. Slower moving oil pump at hot idle, combined with the thinning of the oil once hot, makes for the loss of oil pressure.

If you sit there and start a stone cold engine, take not of the pressure and idle rpm. Either sit there and watch, or come back 10 minutes later and you will find both lower oild pressure and engine idle rpm, with of course, your engine coolant temp gauge being higher.

Now, having the il Pressure light come on, IS an issue. Did you happen to not the mileage on droppoff comapred to you picking it up? Did anyone rag on your truck?

peace
Hog
 

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Discussion Starter · #3 ·
When your oil is cold its much thicker compared to when its hot, thus hot oil building less oil pressure.

Also, your ECM is commanding an idle that is a few hundred rpm higher than it commands once teh engin is warm. Slower moving oil pump at hot idle, combined with the thinning of the oil once hot, makes for the loss of oil pressure.

If you sit there and start a stone cold engine, take not of the pressure and idle rpm. Either sit there and watch, or come back 10 minutes later and you will find both lower oild pressure and engine idle rpm, with of course, your engine coolant temp gauge being higher.

Now, having the il Pressure light come on, IS an issue. Did you happen to not the mileage on droppoff comapred to you picking it up? Did anyone rag on your truck?

peace
Hog
Only 6 miles were put on the truck.
 

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mustve been a hell of a 6 miles :)
 

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I've read that GM has had a lot of problems with the vortec engine. Including low oil pressure. They have determined that a lot of oil problems are from the oil pick up tube o-ring going bad. Gets air bubbles in oil and causes loss of pressure
 

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Take a deep breath, it's nothing serious, provided this has the 5.3L with AFM (Active Fuel Management). Under the oil pressure sender is a screen that filters the oil before it is provided to the AFM lifters... These are extremely common to get gummed up, and cause exactly the problem you describe. You can reach around the back of the intake manifold to access the sender if you don't have gorilla arms, remove the sender, pull out the screen, clean and reinstall. Easy fix. If you can't reach the sender, the hardest part of this job will be pulling to intake to get to it.
 

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Take a deep breath, it's nothing serious, provided this has the 5.3L with AFM (Active Fuel Management). Under the oil pressure sender is a screen that filters the oil before it is provided to the AFM lifters... These are extremely common to get gummed up, and cause exactly the problem you describe. You can reach around the back of the intake manifold to access the sender if you don't have gorilla arms, remove the sender, pull out the screen, clean and reinstall. Easy fix. If you can't reach the sender, the hardest part of this job will be pulling to intake to get to it.
Post a write up, sounds pretty straight forward!
 

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Since your not hearing any noise and there doesn't seem to be any drive ability problems I'd say the oil pressure sensor/sender is to blame. Sounds like when the sensor warns up the electrical internals fail. Very common on GMs
 

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Is there a particular part of the forum I should post this to? Some other forums I'm on are very specific about where and how to post things... Lol
 
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