LB7 oil pump conundrum.

GMCSLEHD

New member
Oct 13, 2006
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Hello all. I built my 2004 LB7 back in 2015. I used Clevite H series bearings for the mains. My build notes show that clearance was .002 inches. That was done with Plastigauge, not a bore gauge, so take it for what it’s worth. I reused my stock oil pump, which mic’d within specs. I also opened up the piston oil squirters to .078 inches

I run a 71 mm turbo and daily drive at about 500 hp. On a sidenote, my cooling stack is clean, and I run a Black stone oil analysis every 5000 miles.

In the past couple years, my oil pressure has dropped to a point where I am not comfortable with it. It’s at 7psi hot idle and 27~30psi at 2000rpm on the CTS3, and a mechanical gauge, when the oil temp get’s over 200°F. This is using Cenpeco 20W50 oil, which helps only until the oil gets above 200°F.

It doesn’t take a lot, especially in warmer weather to get the oil up to 200°. In hot weather I can get it up to 230 without even towing.

Larger piston squirters, combined with the bigger turbo, create the extra heat. Opening up the piston squirters that much, with the stock oil pump, I think creates my lack of oil pressure.

I’m going to pull the motor and replace the oil pump, along with putting on a 2020 oil cooler. I don’t think I want to go to the trouble of putting in an LMl oil pump, etc., so I’m planning on putting in a Melling 316 oil pump and possibly putting stock size pistons squirters back in.

My conundrum is whether the Melling 316 oil pump along with the stock size squirters are going to give me too much oil pressure? Also, whether the larger oil cooler will affect that?

I’m also wondering if there is a benefit to leaving in the oversize oil squirters for cooling the pistons, and whether the Melling 316 will be enough to give me good oil pressure with those oversized squirters and 2020 oil cooler?

I really only want to do this once, so any input would be greatly appreciated.

Thanks!
Josh
 

KyleC4

Tech
Dec 30, 2016
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If your piston squirters were an issue wouldn’t they have caused an issue when this motor first fired off ? Not wait 7 years later ?….. Honestly if I was to pull the motor I’d measure and inspect everything. I personally rarely see oil pump problems. What’s your coolant temps when you see 230 for oil temp?
 

down_hiller

Member
Oct 28, 2016
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8
Is there fuel in your oil? I found out mine had a leaking return line and it would slowly add fuel to my oil and oil pressure would drop to almost nothing. I fixed the leak and my oil pressure has been fine since.
 

Bdsankey

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Feb 1, 2018
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I would only run a GM oil pump. The Melling pumps are FAR too inconsistent in quality to trust IMO. A pinned/shimmed LBZ pump would be a great upgrade over your LB7 pump. I personally don't like running opened up cooling nozzles without increasing oil volume output. The LML pump is ~10-11% larger overall which allows GM to account for the larger hole size.


As for the drop in pressure I agree with KyleC4 that I would have imagined it would have shown it's head early on if it was the piston cooling jets. It may not be a bad idea to check bearing clearances in all the bearings as well as the oil pump to see if it has worn.
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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plasti-gauge is far too inconsistent to know where mains and rod bearing clearances are. if you are on the upper end of the .002 when the engine was new, that would explain the lower pressure now. factory is .0018 IIRC (or around there). combine the large oil squirters and i can very much see the issue.

melling pumps need to be pulled apart and inspected before use. if you can find a reputable place that does this, i wouldnt hesitate to use one. i do like the LML pump as well, just needs either machine work or cover changes IIRC.

eitherway, the upper oil pan has to come off. you might as well check your bearings before deciding on a pump. change the squirters back to stock as well
 

juddski88

Freedom Diesel
Jul 1, 2008
4,431
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Chesterfield, Mass.
I do not believe for one second that even a .003-.004 main/rod bearing clearance would cause that low of pressure...my race engine was super loose with avg. Main/rod bearing clearances of .0035", had enlarged squirters, big turbo oil feed, etc. Did have a new LML pump though with a shimmed regulator and idled hot (240deg f oil temp after a run) at 35-40psi and made 125+psi at 5000k rpm.
 

GMCSLEHD

New member
Oct 13, 2006
9
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1
What pressure are most guys seeing using the melling pump?

Sent from my SM-A426U using Tapatalk
In the searches I did, looks like most people see higher pressures (80psi+) when the oil is cold (using 15w-40), then goes down to around 60psi when warmed up (this is at driving rpms). At idle looks like around 50psi+ cold, and 25psi+ warm. I'm assuming most of these were with stock size piston squirters.


try shimming the oil pressure relief spring
I'll have to do some research on that.

If your piston squirters were an issue wouldn’t they have caused an issue when this motor first fired off ? Not wait 7 years later ?….. Honestly if I was to pull the motor I’d measure and inspect everything. I personally rarely see oil pump problems. What’s your coolant temps when you see 230 for oil temp?
That's what I would think, but I didn't put in a mechanical oil presssure gauge (off of driver's oil galley hole) until 3 years ago. and it seems to have slowly gone down. Maybe I wasn't paying that good of attention to the factory gauge the first couple of years.

Coolant temp always lags behind oil temp by about 10-20 degrees. This is off the CTS3.

Is there fuel in your oil? I found out mine had a leaking return line and it would slowly add fuel to my oil and oil pressure would drop to almost nothing. I fixed the leak and my oil pressure has been fine since.
No fuel in oil. I've run a Blackstone oil analysis the past couple oil changes, seems to look ok.
I would only run a GM oil pump. The Melling pumps are FAR too inconsistent in quality to trust IMO. A pinned/shimmed LBZ pump would be a great upgrade over your LB7 pump. I personally don't like running opened up cooling nozzles without increasing oil volume output. The LML pump is ~10-11% larger overall which allows GM to account for the larger hole size.

As for the drop in pressure I agree with KyleC4 that I would have imagined it would have shown it's head early on if it was the piston cooling jets. It may not be a bad idea to check bearing clearances in all the bearings as well as the oil pump to see if it has worn.

I'm debating on returning the Melling, and getting a pinned and shimmed OEM pump. I've already ordered a set of OEM LB7 piston cooling nozzles to replace the drilled out ones.

I guess I really should check the clearances.

plasti-gauge is far too inconsistent to know where mains and rod bearing clearances are. if you are on the upper end of the .002 when the engine was new, that would explain the lower pressure now. factory is .0018 IIRC (or around there). combine the large oil squirters and i can very much see the issue.

melling pumps need to be pulled apart and inspected before use. if you can find a reputable place that does this, i wouldnt hesitate to use one. i do like the LML pump as well, just needs either machine work or cover changes IIRC.

eitherway, the upper oil pan has to come off. you might as well check your bearings before deciding on a pump. change the squirters back to stock as well

I now know plastigauge is not ideal, I did not know that back when I built the motor (first engine build).

When you say pulled apart and inspectected, are you referring to gear size and clearances?

Looks like I'll be picking up a bore gauge to check clearances.

I've got stock squirters to go back on.

I do not believe for one second that even a .003-.004 main/rod bearing clearance would cause that low of pressure...my race engine was super loose with avg. Main/rod bearing clearances of .0035", had enlarged squirters, big turbo oil feed, etc. Did have a new LML pump though with a shimmed regulator and idled hot (240deg f oil temp after a run) at 35-40psi and made 125+psi at 5000k rpm.

I honestly don't know. The motor has run trouble free (minus the low oil pressure) for 75,000 miles since I rebuilt it.


Thank you all for your replies!