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O3. LB7 no oil pressure.?

Old 01-11-2021, 09:30 PM
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Default O3. LB7 no oil pressure.?

I have a lb7 with around 200,000 miles. And all of a sudden one morning when I cranked it up my dash lights up no oil pressure and the gage reads the same?
I replaced the sending unit. Still no pressure. So I removed the sending unit and cranked it for a few seconds and no oil came out at all
so I removed the oil filter and still no oil coming out.
The engine sounds great. has no nock, tic, or no chatter.
Is ther any other possible things to check before I pull the motor out and replace the pump?
I put all new injectors in it 3 months ago.
Old 01-11-2021, 09:39 PM
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Probably a bad oil pump. Hook up a mechanical oil pressure gauge and see if you have oil pressure. If you do then it's something electrical if you don't then most likely a bad oil pump.
Old 01-12-2021, 06:34 AM
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oil pump lost prime
Old 01-12-2021, 07:16 AM
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There is probably a pressure release valve to limit the max pressure from the pump. If it's stuck open it will severely limit the pressure to the filter.
Old 01-12-2021, 11:40 AM
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Anyone know were the pressure release valve is on a lb7?
Old 01-12-2021, 12:39 PM
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Try calling Matt at the Diesel Barn. He's in Crawfordville and has been a huge help to me with my LB7. I will PM you his phone number.
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Old 01-12-2021, 12:45 PM
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Make sure there is plenty of oil in the sump, put it to the full line on the stick.

Take filter off and use a shop vac to suck on the port off to the side of the central threaded port. That is the port where oil enters from pump. Suck on it til oil shows up. Screw on filter and crank engine.

That should reprime the pump.

Did engine sit for an extended period of time?
Old 01-12-2021, 01:15 PM
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Originally Posted by TrueGrain View Post
Anyone know were the pressure release valve is on a lb7?
Normally they're on the filter housing or on the fitting where the pressure sensor/switch in located but not sure on that engine. It will look like a large bolt and have a spring and rod inside.
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Old 01-12-2021, 01:43 PM
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Originally Posted by Corndog38 View Post
Make sure there is plenty of oil in the sump, put it to the full line on the stick.

Take filter off and use a shop vac to suck on the port off to the side of the central threaded port. That is the port where oil enters from pump. Suck on it til oil shows up. Screw on filter and crank engine.

That should reprime the pump.

Did engine sit for an extended period of time?
Just over night. I replaced all the injectors a few months ago so I keep an eye on the oil pressure gauge. One day it was working fine next day it was on 0. It's a daily driver so it has been sitting up before that either prior to 3 months .
Old 01-12-2021, 03:17 PM
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My boat did that and it was the oil pump that had lost prime because I let it drain overnight.

BTW, crap oil filters (won't mention any names since it seems to start a flame war around here but they rhyme with CRAM) can cause this.
Old 01-12-2021, 06:47 PM
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Did you reuse that oil filter? Anti drainback valve could not be working, and some filters don't have one. I'd buy a delco oil filter and put it on and see if issue persists.

Have put nearly 200k on my lbz and always used either delco, donaldson, or napa gold filters. Haven't had any issues, but this would be the simplest and easiest explanation. Don't think it could have air locked overnight, that's generally a new or rebuilt motor issue.
Old 01-12-2021, 06:56 PM
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I’m not a diesel guy do they have Gerotor oil pumps driven off the crank like the Chevy/Ford gas engines? Pretty sure they can’t lose prime unless something is compromised as the gears physically hold oil in them. Usually a pickup oring or worn pump/ pressure relief causes it.

Last edited by JExpedition07; 01-12-2021 at 07:06 PM.
Old 01-12-2021, 07:13 PM
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Good thread here. Since you've replaced the sender, probably sensor
https://www.duramaxdiesels.com/forum...nothing.12433/

extremely unlikely it's a bad oil pump. They fail very rarely, and if it was bad, it would not sound normal at startup.

Could crack turbo oil feed and see if getting oil when cranking. From center of valley to top of turbo. My bet is the sensor being bad.

Also will want to confirm you don't have diesel in the oil/making oil being a lb7.

Old 01-12-2021, 07:43 PM
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He removed the oil filter and cranked it, no oil flow. That is an oil pump that has lost prime. Not a filter problem, not a sender problem.
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Old 01-12-2021, 07:57 PM
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Originally Posted by Corndog38 View Post
Make sure there is plenty of oil in the sump, put it to the full line on the stick.

Take filter off and use a shop vac to suck on the port off to the side of the central threaded port. That is the port where oil enters from pump. Suck on it til oil shows up. Screw on filter and crank engine.

That should reprime the pump.

Did engine sit for an extended period of time?
I tried your suggestion with a pretty good shop vac for 15 minutes and I couldn’t get any oil to come out.
Old 01-12-2021, 08:09 PM
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Originally Posted by dawgsfish View Post
Did you reuse that oil filter? Anti drainback valve could not be working, and some filters don't have one. I'd buy a delco oil filter and put it on and see if issue persists.

Have put nearly 200k on my lbz and always used either delco, donaldson, or napa gold filters. Haven't had any issues, but this would be the simplest and easiest explanation. Don't think it could have air locked overnight, that's generally a new or rebuilt motor issue.
No sir, I replaced the filter when I replaced the sending unit. Then removed the filter all together. I use Delco
Old 01-12-2021, 08:38 PM
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Ten four. I missed that you cranked with oil filter off. That's definitely odd
Old 01-13-2021, 08:00 AM
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Originally Posted by dawgsfish View Post
Ten four. I missed that you cranked with oil filter off. That's definitely odd
It probably is the pump but I would hate to go through the expense of replaying it and find out it was something else.
Old 01-13-2021, 12:13 PM
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Originally Posted by TrueGrain View Post
It probably is the pump but I would hate to go through the expense of replaying it and find out it was something else.
I would seriously check the pressure release before changing the oil pump.
Old 01-13-2021, 02:08 PM
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If any of the regulating/relief valves were stuck, I would still expect at least some oil flow out of the filter head with filter off.

Also, on shutdown the day before he presumably had good oil pressure. The valves were working then.

Kinda thinking he might have drive gear damage like that one on utube.

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