Oil pressure questions
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From: So Cal
Oil pressure questions
My oil pressure seems to be low, im pretty sure a new pump will fix it but i just want to get a couple more opinions. A quick background, forged 346 with "high tollerance" clearances, d1 procharger, ported ls6 pump, mobil1 15-50, ac delco pf46 filter. 65* oil temp shows pressure around 45psi and 200* oil temp shows 12psi at 850rpm idle. Driving around at about 2500rpm gets to about 30psi. What are your thoughts? Ive ordered a mellings hv hp pump but havent installed it yet, hoping this will fix it. The car hadnt run in 3-4 years before getting it all back together earlier this week
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From: Howell Michigan
St. Jude Donor '09-'10-'11
My oil pressure seems to be low, im pretty sure a new pump will fix it but i just want to get a couple more opinions. A quick background, forged 346 with "high tollerance" clearances, d1 procharger, ported ls6 pump, mobil1 15-50, ac delco pf46 filter. 65* oil temp shows pressure around 45psi and 200* oil temp shows 12psi at 850rpm idle. Driving around at about 2500rpm gets to about 30psi. What are your thoughts? Ive ordered a mellings hv hp pump but havent installed it yet, hoping this will fix it. The car hadnt run in 3-4 years before getting it all back together earlier this week
"AlohaC5" Senior Member
Joined: Jun 2003
Posts: 3,562
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From: Madison, AL
12psi at 850 RPM idle is definitely a problem.
Lets break this down.
Ported LS6 oil pump... Check
Mobil 15W50 oil... Check
Oil Temperature 200*... Check
AC Delco PF46 oil filter... Check
Forged 346.... How long ago did you have the forged motor built, and have you always experienced low oil pressure when the engine is hot?
The car hasn't been run in 3 to 4 years... "Got it all back together earlier this week".
What does that mean? What was assembled earlier this week and what is its connection to the oil system?
I'm not convinced that a Mellings High Volume HP Pump will resolve the low oil pressure issue.. yet.
Crazy question, did you check your oil level? Are there any oil leaks?
Was this the same oil and filter that's been sitting in the car for the past 3 to 4 years? or did you do an oil change?
Lets break this down.
Ported LS6 oil pump... Check
Mobil 15W50 oil... Check
Oil Temperature 200*... Check
AC Delco PF46 oil filter... Check
Forged 346.... How long ago did you have the forged motor built, and have you always experienced low oil pressure when the engine is hot?
The car hasn't been run in 3 to 4 years... "Got it all back together earlier this week".
What does that mean? What was assembled earlier this week and what is its connection to the oil system?
I'm not convinced that a Mellings High Volume HP Pump will resolve the low oil pressure issue.. yet.
Crazy question, did you check your oil level? Are there any oil leaks?
Was this the same oil and filter that's been sitting in the car for the past 3 to 4 years? or did you do an oil change?
Last edited by Gray Ghost GS; Dec 29, 2011 at 08:28 PM.
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Joined: Oct 2011
Posts: 69
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From: So Cal
12psi at 850 RPM idle is definitely a problem.
Lets break this down.
Ported LS6 oil pump... Check
Mobil 15W50 oil... Check
Oil Temperature 200*... Check
AC Delco PF46 oil filter... Check
Forged 346.... How long ago did you have the forged motor built, and have you always experienced low oil pressure when the engine is hot?
The car hasn't been run in 3 to 4 years... "Got it all back together earlier this week".
What does that mean? What was assembled earlier this week and what is its connection to the oil system?
I'm not convinced that a Mellings High Volume HP Pump will resolve the low oil pressure issue.. yet.
Crazy question, did you check your oil level? Are there any oil leaks?
Was this the same oil and filter that's been sitting in the car for the past 3 to 4 years? or did you do an oil change?
Lets break this down.
Ported LS6 oil pump... Check
Mobil 15W50 oil... Check
Oil Temperature 200*... Check
AC Delco PF46 oil filter... Check
Forged 346.... How long ago did you have the forged motor built, and have you always experienced low oil pressure when the engine is hot?
The car hasn't been run in 3 to 4 years... "Got it all back together earlier this week".
What does that mean? What was assembled earlier this week and what is its connection to the oil system?
I'm not convinced that a Mellings High Volume HP Pump will resolve the low oil pressure issue.. yet.
Crazy question, did you check your oil level? Are there any oil leaks?
Was this the same oil and filter that's been sitting in the car for the past 3 to 4 years? or did you do an oil change?
Sorry for the vague description, but it was torn down for new head gaskets years ago and only got the heads back on before it sat. I reinstalled basically all the bolt ons with the short block being untouched since the build.
I have changed all the fluids in the car. Actually changed the oil twice because the first time i used 5w30 and was only seeing 9psi hot @ idle, so i dumped that oil and replaced it with the 15w50. I have tripple checked the oil
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Joined: Oct 2011
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From: So Cal
Here is my thinking... Either the relief spring in the pump has weakened/stuck from sitting for so long, the oil pick up may be somewhat blocked or restricted, or there is something else going on. Maybe the bearings are pounded out? Im really just taking a shot in the dark with replacing the pump thinking this is the most viable option
"AlohaC5" Senior Member
Joined: Jun 2003
Posts: 3,562
Likes: 44
From: Madison, AL
I would definitely use a mechanical pressure gauge and contact the engine builder to see if he has any recommendations. I don't know how well you knew the previous owner, but when you say, "I recently bought the car and am not 100% sure it has always been low." it makes you wonder if he sold the car because he knew it had a low oil pressure problem for some unknown reason. I don't want to sound pessimistic..but.
Last edited by Gray Ghost GS; Dec 29, 2011 at 09:03 PM.
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From: So Cal
I would definitely use a mechanical pressure gauge and contact the engine builder to see if he has any recommendations. I don't know how well you knew the previous owner, but when you say, "I recently bought the car and am not 100% sure it has always been low." it makes you wonder if he sold the car because he knew it had a low oil pressure problem for some unknown reason. I don't want to sound pessimistic..but.
Ill get a mechanical gauge on it possibly tomorrow before i tear it down for the new pump. I have a feeling the bearings have seen their better days and am hoping the HV of the new pump will prolong the life of the bottom end
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My oil pressure seems to be low, im pretty sure a new pump will fix it but i just want to get a couple more opinions. A quick background, forged 346 with "high tollerance" clearances, d1 procharger, ported ls6 pump, mobil1 15-50, ac delco pf46 filter. 65* oil temp shows pressure around 45psi and 200* oil temp shows 12psi at 850rpm idle. Driving around at about 2500rpm gets to about 30psi. What are your thoughts?
If it gets up towards 70 psi, then the oil pump's pressure relief valve is working correctly and the low oil pressure at lower RPM is probably due to loose clearances in the motor.
Last edited by ZeeOSix; Dec 29, 2011 at 09:38 PM.
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From: Howell Michigan
St. Jude Donor '09-'10-'11
Things that can cause low oil pressure:
Stuck oil pressure relief.
Bad oil filter.
Blocked pickup tube screen.
Bad, pinched o'ring at the pickup tube to oil pump.
Bad oil pump.
Low oil level.
Bad oil pressure sending unit.
When oil pressure is low the valvetrain will make noise.
Stuck oil pressure relief.
Bad oil filter.
Blocked pickup tube screen.
Bad, pinched o'ring at the pickup tube to oil pump.
Bad oil pump.
Low oil level.
Bad oil pressure sending unit.
When oil pressure is low the valvetrain will make noise.
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Things that can cause low oil pressure:
Stuck oil pressure relief.
Bad oil filter.
Blocked pickup tube screen.
Bad, pinched o'ring at the pickup tube to oil pump.
Bad oil pump.
Low oil level.
Bad oil pressure sending unit.
When oil pressure is low the valvetrain will make noise.
Stuck oil pressure relief.
Bad oil filter.
Blocked pickup tube screen.
Bad, pinched o'ring at the pickup tube to oil pump.
Bad oil pump.
Low oil level.
Bad oil pressure sending unit.
When oil pressure is low the valvetrain will make noise.
it was mushroomed in the head...had to pull the cam to remove the lifter
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Posts: 2,843
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From: Howell Michigan
St. Jude Donor '09-'10-'11
this can also cause low oil pressure like the OP described.....car never made a noise and ran fine....
Attachment 47687478
Attachment 47687479
it was mushroomed in the head...had to pull the cam to remove the lifter
Attachment 47687480
Attachment 47687478
Attachment 47687479
it was mushroomed in the head...had to pull the cam to remove the lifter
Attachment 47687480
Thread Starter
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Joined: Oct 2011
Posts: 69
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From: So Cal
What kind of oil pressure do you see with oil at 200 deg F and RPM held at 5000 until the pressure stabilizes?
If it gets up towards 70 psi, then the oil pump's pressure relief valve is working correctly and the low oil pressure at lower RPM is probably due to loose clearances in the motor.
If it gets up towards 70 psi, then the oil pump's pressure relief valve is working correctly and the low oil pressure at lower RPM is probably due to loose clearances in the motor.
Things that can cause low oil pressure:
Stuck oil pressure relief.
Bad oil filter.
Blocked pickup tube screen.
Bad, pinched o'ring at the pickup tube to oil pump.
Bad oil pump.
Low oil level.
Bad oil pressure sending unit.
When oil pressure is low the valvetrain will make noise.
Stuck oil pressure relief.
Bad oil filter.
Blocked pickup tube screen.
Bad, pinched o'ring at the pickup tube to oil pump.
Bad oil pump.
Low oil level.
Bad oil pressure sending unit.
When oil pressure is low the valvetrain will make noise.
Your post got me to thinking maybe the o ring rotted? seeing as it was used then parked for about 3 years...this can also cause low oil pressure like the OP described.....car never made a noise and ran fine....
Attachment 47687478
Attachment 47687479
it was mushroomed in the head...had to pull the cam to remove the lifter
Attachment 47687480
Attachment 47687478
Attachment 47687479
it was mushroomed in the head...had to pull the cam to remove the lifter
Attachment 47687480
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From: So Cal
a quick update.. I pulled the oil pump out to find out it had a melling m295 pump in it with a couple small washers as shims. Everything looked ok with the pump but the pressure relief piston moved ok towards the top of the bore, but when trying to remove it it would get stuck toward the bottom of the bore. It took a good amount of force to get it unstuck and out. Im going to go ahead and install the HV HP melling pump and report back
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I swear you would have never known that lifter was toast....
not any indication at all....until oil pressure went to 0 THEN 
on steering wheel