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stuck oil relief valve?

Chris Bassett
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swathdiver Senior Enthusiast

swathdiver

Posted
Posted

Make sure that whoever does your pump uses the big pump and not the little one.  The aluminum LC9 uses the Melling M365/12612289.

  • 2 months later...
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Dnt
Dnt

Did you clean the screen filter behind the oil pressure sending unit before you put the new one on? If not that is most likely your issue. There is a pretty good chance here that they would replace th

swathdiver
swathdiver

Your truck has the Melling M365 oil pump.  Maximum oil pressure is 33 psi with the yellow spring in this pump.  The red spring had the oil pressure relief set at 43 psi in the earlier trucks.  The 365

GhostWriter
GhostWriter

An interesting read.  Many 5.3 AFM engine owners have asked the same questions.  In no particular order, here are some additional things to consider:   1)  Before posting, have your local pa

maddss99 New Member

maddss99

Posted
Posted

Did you ever figure out what the cause of the low oil pressure?   Pump, O-Ring or Relief valve ?

  • 1 year later...
  • 9 months later...
  • 2 months later...
Pete Lines New Member

Pete Lines

Posted
Posted

I am also wondering if he figured it out..  Let me explain my problem with my 2012 5.3 lc9 which started with a stuck afm lifter. 

  • I replaced all lifters,
  • new vlom screen and sending unit
  • valve job, heads shaved
  • After this it ran fine but within a week noticed my pressure began to drop (normally 40 at speed, and 25 at idle)
  • Currently its 10 at speed and near zero at idle but no noise and runs smooth.
  • I took a manual reading on the top of the engine and at the bottom (oil filter)  lower pressure appears normal 40 around and goes up to near 60 at 2K rpms top reading is the same as the gauge inside truck.
  • I began running 10w-40 with a quart of Lucas oil treatment, pressure was up enough that the alarm did not go on
    • I know, not really a good idea
  • I had done the simple check for the O ring for the oil pump, parked on a steep hill and over filled oil.
  • After driving 10K miles with 10w-40 and Lucas oil treatment the pressure has dropped more and now alarms all the time.
  • I tried the ac 48 and ac 64 filters
  • I thought maybe I had a defective vlom and it was spilling oil so I put the old one back, same problem  then put the new one again
  • I decided to change the oil pump with a mellings 365 same problem still 

Now I am thinking the following:

bad oil pressure relief valve in the pan by the oil filter?

or worn bearings

 

I am really at a loss, I have put so much time into all this work.

thanks for any help

Pete

 

Chevy V8 New Member

Chevy V8

Posted
Posted

! hate to be the bearer of bad news but it sounds like your cam bearing is walking out. Watch the (ultimate ls engine low oil pressure) video on youtube to see the rest of the story. Same thing happened to my 6.0 and I'm rebuilding it right now.

  • 1 year later...
Oakleytwin New Member

Oakleytwin

Posted
Posted

Same thing with my truck, replaced oil pressure sensor and oil pump and still the engine light comes on and low pressure stop engine warning comes on. GM said it could be the relief valve. 

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