Low/erratic oil pressure when hot
02-20-2014, 01:42 AM
#1
Staging Lane
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Low/erratic oil pressure when hot In the past I have spun a rod bearing, it sounded like a marble against a metal pan. No noise here like that.
Built the motor less then 10,000 miles ago, did something stupid, drove down 500 miles to meet my mom. We did multiple burnouts back to back and spun the bearing.
Got home pulled the head replaced the rod, installed new rod bearings and main bearings and checked the crank, it was good.
Now I have normal oil pressure when cold, 60-80...Actual mechanical gauge showed 100 at higher cold rpms...Ported and polished melling pump and shimmed for 10 psi extra at WOT.
After running it up to operating temp I see the oil pressure bouncing from 30-40 very fast at idle or driving below 2k RPMS. Gets more sporadic with a load such as 6th gear at 50mph. Mechanical gauge wasn't as quick but still showed erratic readings. Give it a little throttle and it goes away if closer to 2k RPMS. But if I am accelerating my oil pressure drops about 5 psi and picks back up after letting off if I'm closer to 3k+ RPMS.
I ran two 0-100 runs today and saw oil pressure as low as 25 psi and still being erratic. Also was the first time I noticed my AFR gauge was leaning out every few seconds consistantly. I saw this going about 30 mph after the run and saw afr would be vibrating around 15:1 for a few seconds and then spike to 17.5:1 and go back. I am OLSD because of my leaking exhaust on the passenger side, not my WB side.
Likely cause for this behavior maybe bad tolerance in my main bearings? Cam bearings? I can't see many other options. I need some opinions here before I put my turbo back on. As soon as I get my tax return I want to drop the pan and run plastigauge on the rods and mains and check the tolerances. But cam bearings means me yanking the motor
.
Built the motor less then 10,000 miles ago, did something stupid, drove down 500 miles to meet my mom. We did multiple burnouts back to back and spun the bearing.
Got home pulled the head replaced the rod, installed new rod bearings and main bearings and checked the crank, it was good.
Now I have normal oil pressure when cold, 60-80...Actual mechanical gauge showed 100 at higher cold rpms...Ported and polished melling pump and shimmed for 10 psi extra at WOT.
After running it up to operating temp I see the oil pressure bouncing from 30-40 very fast at idle or driving below 2k RPMS. Gets more sporadic with a load such as 6th gear at 50mph. Mechanical gauge wasn't as quick but still showed erratic readings. Give it a little throttle and it goes away if closer to 2k RPMS. But if I am accelerating my oil pressure drops about 5 psi and picks back up after letting off if I'm closer to 3k+ RPMS.
I ran two 0-100 runs today and saw oil pressure as low as 25 psi and still being erratic. Also was the first time I noticed my AFR gauge was leaning out every few seconds consistantly. I saw this going about 30 mph after the run and saw afr would be vibrating around 15:1 for a few seconds and then spike to 17.5:1 and go back. I am OLSD because of my leaking exhaust on the passenger side, not my WB side.
Likely cause for this behavior maybe bad tolerance in my main bearings? Cam bearings? I can't see many other options. I need some opinions here before I put my turbo back on. As soon as I get my tax return I want to drop the pan and run plastigauge on the rods and mains and check the tolerances. But cam bearings means me yanking the motor
. 
02-21-2014, 11:11 PM
#3
If you're not sensing a loss of power, I would focus on the oil pump spring & valve.
I would think that a bearing problem would show as a proportional loss of pressure across the RPM range.
Another culprit could be the oil galley barbell w/o-ring. I had a similar problem as yours, and this was at fault. I suspect that the o-ring had dried out over time, after the engine sat on a palate for years. Under acceleration, the barbell would move in the galley.
Do you have any metal chips in the oil or the filter?
I would think that a bearing problem would show as a proportional loss of pressure across the RPM range.
Another culprit could be the oil galley barbell w/o-ring. I had a similar problem as yours, and this was at fault. I suspect that the o-ring had dried out over time, after the engine sat on a palate for years. Under acceleration, the barbell would move in the galley.
Do you have any metal chips in the oil or the filter?
02-22-2014, 01:35 AM
#4
Staging Lane
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Wow... You just opened up my world. This may be something I investigate. I have educated myself a little on this barbell theory. My problem is most searches lead me to not installing the barbell or something of that nature. Lets pretend when I sent my 02 ls6 block in to get cleaned this barbell was left in. this may have caused my problems? I feel this may be it. What damage are we possibly talking about if this barbell has a detieriorated o-ring? Are my cam bearings likely toasted?
Thank you for enlightening me and teaching me that learning is never over.
Thank you for enlightening me and teaching me that learning is never over.
02-22-2014, 08:09 PM
#6
I watched the video. Why are the RPMs retreating to 500?
Unless you have chips in the oil & the filter, I wouldn't dwell on the bearings.
Not to predetermine what the cause is, because there could be an issue with the pressure relief in the oil pump....there are three scenarios with the barbell> The builder 1) either left the original in 2) removed then reused the original 3) replaced it with a new one.
Since you have verified the erratic readings with a mechanical gauge, this rules out the sensor.
Unless you have chips in the oil & the filter, I wouldn't dwell on the bearings.
Not to predetermine what the cause is, because there could be an issue with the pressure relief in the oil pump....there are three scenarios with the barbell> The builder 1) either left the original in 2) removed then reused the original 3) replaced it with a new one.
Since you have verified the erratic readings with a mechanical gauge, this rules out the sensor.
Last edited by gMAG; 02-22-2014 at 08:23 PM.
02-23-2014, 01:05 PM
#7
Staging Lane
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They are going down when I was idling because I put a load on the motor... letting the clutch engage a little to show oil dropping at lower rpms. I remember it going real low even without the oiling problems though.
Lol I am the builder and you are right. I was unaware about the barbell and when I I dipped the ls6 block I left it in which means it is probably deteriorated. Ill update this post when I replace the barbell.
Last note for now is I believe the erratic behavior is related im not sure if the drop in pressure is related. I feel the bearings are in question but until I fix my known problem that will be determined another day. As far as the relief valve on the pump I hope that is not it, low mileage on a brand new melling but I did dick with it with another experienced builder and we shimmed it for 10 psi extra and ported/polished it. I wanted a little extra because the oil the turbo is leeching off of it.
Thanks your time and help, I dont think I could have came to this solution without you.
Lol I am the builder and you are right. I was unaware about the barbell and when I I dipped the ls6 block I left it in which means it is probably deteriorated. Ill update this post when I replace the barbell.
Last note for now is I believe the erratic behavior is related im not sure if the drop in pressure is related. I feel the bearings are in question but until I fix my known problem that will be determined another day. As far as the relief valve on the pump I hope that is not it, low mileage on a brand new melling but I did dick with it with another experienced builder and we shimmed it for 10 psi extra and ported/polished it. I wanted a little extra because the oil the turbo is leeching off of it.
Thanks your time and help, I dont think I could have came to this solution without you.
Last edited by ChevyAllTheWay; 02-23-2014 at 01:22 PM.
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03-05-2014, 08:47 PM
#9
Staging Lane
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And the verdict is...not the rear oil diverter plug"barbell". Picked it up at the dealership for about $8.40. Ill be yanking my valve covers soon and double check my arp studs as they have came loose on me once before just to eliminate that possibility. I will check my main and rod clearences withen the next couple of weeks, oil change is due in about 900 miles anyway so ill do that at the same time to save some money. Ill check back in when I have done those things. If anybody wants to offer some more advice I am all ears.
03-05-2014, 08:51 PM
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Staging Lane
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Side note. Multiple oil changes with same issue, heavier weight with same issue.
I'll look at the oil pump when the pan is off. What will I be looking for if the relief valve is bad? Seizing? To loose? Broken spring? Ill search but if you can give me a better idea what I am looking for it would be appreciated.
I'll look at the oil pump when the pan is off. What will I be looking for if the relief valve is bad? Seizing? To loose? Broken spring? Ill search but if you can give me a better idea what I am looking for it would be appreciated.
03-07-2014, 02:11 AM
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Not a lot. But I figured that I didnt have any chunks and the rods are the last to get oil so it should have been caught in the filter. If it got passed that then it should have been insignificant. Unfiltered oil does go through the pump though so if some stuff got in there that may be my erratic readings... relief valve may have some stuff in there.
I'll be pulling the pan soon to check bearings. I have a feeling it is mains based off my research. Also I have had a vibration for a while now and after I reinstalled trans, drive shaft, clutch, flywheel it disappeared. I have a feeling the vibration sent itself to the crank. Maybe root cause if my mains are bad? Wish I knew what fixed my problem. Incorrect installation of one of those parts must have been the culprit.
I'll be pulling the pan soon to check bearings. I have a feeling it is mains based off my research. Also I have had a vibration for a while now and after I reinstalled trans, drive shaft, clutch, flywheel it disappeared. I have a feeling the vibration sent itself to the crank. Maybe root cause if my mains are bad? Wish I knew what fixed my problem. Incorrect installation of one of those parts must have been the culprit.
03-07-2014, 06:06 AM
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Crap, started more research. I did not know plastigauge was so inaccurate. My plan was to plastigauge my mains and rods with the crank in the motor. I feel the oil pump may be in question but I am also afraid my vibration may have screwed my crank up. Best advice for a man not looking to pull the motor and basically do another rebuild? If my relief valve is messed up a little can I fix it or replace the whole pump? The drop in pressure under acceleration has to mean bad oil clearence right, not just the pump? I have a total of $500 I am allowed to spend on my car and was hoping to install my turbo back with a new $100 scavenge pump.
03-07-2014, 01:09 PM
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Just to clarify something here and I need to continue my research on this matter. Work is 20 miles away almost all Highway. If I go all the way to work and keep rpms down to 2500 or less I can make it to work and idle 40 psi like normal. However if I do the same and do a quick sprint .1 miles away from work bringing rpms to 4500 I immediately see my oil pressure acting up again and sitting around 30. When the oil is a little bit cooler I can still see the fluctuations although it is very minor. So I know I'm dealing with oil temperature issue.
Is it possible for oil pumps to cause my 5+ psi oil drops under acceleration? The relief valve I agree with causing erratic behavior. I will attempt to check my crank end play tomorrow using a dial indicator and crank pulley.
Is it possible for oil pumps to cause my 5+ psi oil drops under acceleration? The relief valve I agree with causing erratic behavior. I will attempt to check my crank end play tomorrow using a dial indicator and crank pulley.
03-21-2014, 01:02 AM
#17
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Replaced oil pump. Removed my melling 10295 with a melling 10296. Although it seems my oil pressure is a bit higher now it hasn't solved my erratic oiling problem. Changed my oil and filter while I was down there.
Other thoughts? Still need to see my endplay is.
Other thoughts? Still need to see my endplay is.
