Oil pressure 10-11psi hot idle, fresh rebuild

[Anotherduramax]

Newly built LMM, new oil pump, added compounds, 2020 L5P oil cooler and filter. Where is the best place to hook a mechanical gauge, or are the oil sending units a common failure? Any input would be appreciated. I have only started it a few times, I have not even broken it in yet, just looking for suggestions, thank you. Here is a picture as it sits, it’s getting close, I hope.

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[ikeG]

I've ran an oil pressure sender in the front oil gallery plug, drivers side. Normally this one is free for the use because you get your compounds oil supply from the same plug, on the passenger side.

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[Anotherduramax]

Awesome, I will get an adapter and get one installed, would you guys recommend a permanently installed one, or just have one in while troubleshooting?


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[ikeG]

If you are just going to use it to troubleshoot, you could surely borrow or rent a mechanic's setup?

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[Anotherduramax]

Verified with a mechanical gauge, I drop to 10-11psi hot idle, I’ll be pulling the pan and front cover when I get some time.

This is all that was on my magnetic drain plug, newly rebuilt motor, I will cut open the filter and see if maybe the oil pump left anything in the filter.


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[Anotherduramax]

The only metal that I know is black, at least coated black is the gears on the oil pump. If that is the case does anyone have good recommendations on an oil pump? Switch to an LML or run a Melling pump?


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[DAVe3283]

What about putting the original pump back in?

I get upgrading to a higher flow oil pump, but I have never understood why people replace the oil pump with a new identical unit. When I built my motor, I left the stock oil pump alone. 50k miles on the build, and 350k miles on the oil pump, still holds great pressure. IMO oil pumps don't wear out on the Duramax. Putting a new one on takes you from a known good pump to an unknown.

Did you set up your bearing clearances looser than stock? If so, you probably need to upgrade to a higher flow oil pump. The other thing I have heard of is one or more of the oil squirters falling off, and it flows too much oil and can't build good pressure.

 

[Anotherduramax]

Ya i wanted a fresh oil pump, everything else was new so it made sense in my mind, I used a new LMM oil pump from the dealer. I’m hoping I see something during teardown. Bearing clearance is opened a little on the mains, but still within factory spec, just the higher end. .025


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[Chevy1925]

make sure the freeze plug is in the oil galley above the oil pump. What is pressure when cold? What pump did you use? new gasket on the pump pickup?

 

[Anotherduramax]

Yes new gasket, using an oem LMM pump and startup oil pressure is right at 65-70psi


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[Chevy1925]

that wont be a oil galley plug then unless its cocked to one side and bleeding off pressure.

how did you measure bearing clearance? what are the rods at for clearance? did this truck ever have low oil pressure prior to the rebuild?

 

[Anotherduramax]

Bore gauge and Mic for clearance, then checked with plastigauge, rods are .019-.019. No oil pressure issues at all prior to the rebuild, just looking for a little extra power. It helps talking through all of this though, I just need to find the time to open it all back up, but any leads on what to look for help.


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[Chevy1925]

well assuming the bearings are good inside (and i would definitely check them all now), i would say its either a leaky oil pressure relief valve thats in the front cover on the pass side (may have even forgot the o-ring there or it fell out as the cover went on?) or its just a bad pump. i would for sure check to make sure all o-rings are in place on the pump side and pressure relief side.

 

[JoshH]

What is your hot oil pressure at 1800 RPM? What weight oil are you running?

 

[Anotherduramax]

What is your hot oil pressure at 1800 RPM? What weight oil are you running?

36-44psi at 1800 it’s hard to read exactly on the gauge, and using 15w40


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[Chevy1925]

yeah your running border line "GM Spec" which is 7 psi idle and 28 psi at 1800rpm. what port did you check with the mechanical gauge?

 

[Anotherduramax]

yeah your running border line "GM Spec" which is 7 psi idle and 28 psi at 1800rpm. what port did you check with the mechanical gauge?

The first port on the drivers side.


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[JoshH]

The data I have calls for minimum 14 psi hot idle and 42 psi at 1800 RPM. I would try bumping the oil up to 20w50 and see what that does for you.

 

[Chevy1925]

My reply was per GM's service information. i have not looked at the older years but i wonder if they have changed it

 

[JoshH]

They must have changed it with the LML.