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Old 12-11-2008, 09:10 PM   #1 (permalink)
07GreyLBZ
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8.1 Low Oil Pressure @ Idle

I recently purchased a 2003 2500hd w/ the 8.1 and Allison combo that had 129,000 miles on it. The past history of truck usage/maintanance in unknown at this point in time. When the oil is warm the gauge indicates an oil pressure of approx. 5 psi. Driving down the road it is between 25-40psi. I have never had an 8.1 and am unfamiliar with its operating tendancies. My question is, is this normal or am I looking at a partially plugged oil pickup screen or an engine rebuild?? Any help would be greatly appreciated.
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Old 12-11-2008, 11:21 PM   #2 (permalink)
07GreyLBZ
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Any ideas, or is that just normal for that engine?
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Old 12-11-2008, 11:31 PM   #3 (permalink)
dieselholic06
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I can't remember the exact #, but they do have a VERY LOW pressure @ idle.

It should be a good truck for you.
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Old 12-12-2008, 12:11 AM   #4 (permalink)
matt4270
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I don't pay attention to what the numbers are on the gauge, but during a warm idle, my gauge is at the first mark on the left side (1/4?). On cold start, in winter, it's 3/4 or slightly above, and crusing warmed up at 70-75, maybe 2200-2300 rpm, it's in the middle or slightly to the right. If it seems to run smoothly and has good power and feels right, I would worry more about the gauge sender or calibration. Hope this helps!
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Old 12-12-2008, 01:03 AM   #5 (permalink)
Sir-Col
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Hello, your oil pressure is about normal for the 8.1 with 5-30 oil. I was told that the idle psi is aprx 1 psi for every 100 rpm, therefor your idle speed at 500 rpm would give you 5psi. Straight 30wt. oil , or 10-30, or 10-40 will improve the idle psi somewhat.
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Old 12-12-2008, 07:54 AM   #6 (permalink)
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That's too low, but I would check it with a real gauge to make sure your electronic system is accurate. If your sending unit is dripping oil it's bad and no need to go any further just replace it.

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Old 12-12-2008, 09:30 AM   #7 (permalink)
Vin63
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My 8.1L oil pressure on the gauge appeared low, as well. My oil analyses always came back normal. You can use an oil stabilizer to help increase oil pressure. And, check the oil level regularly...I used my 8.1L to tow pretty heavy and and it would consume oil from time to time, adding to the low indication on the oil pressure gauge.
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Old 12-12-2008, 09:54 AM   #8 (permalink)
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definitely not uncommon with 454s or 8.1s... If there is no valve train clicking or rattling, I wouldn't worry about it. A friend has a 300 000 mile vortec 454 and he still tows regularly with it with no problems despite 5 psi idle oil pressure.

I am sure 10-30 or 10-40 would reduce some oil consumption and increase pressure, as my understanding that the factory spec'd 5-30 due to fuel economy. With the looser tolerances of a well broken in engine, a heavier weight oil shouldn't hurt.

Be sure to note, oil level does not imapct oil pressure (unless it is critically low or perhaps being way too high to the point the crank is whipping it into a froth).

The only things that impact oil pressure are viscosity, rate and tolerances. A poorly performing pump could reduce rate to the point the pressure would decrease, which would be bad, but since you see the increase with rpm, I don't think you have a problem.

Last edited by Ramv; 12-12-2008 at 09:59 AM.
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Old 12-12-2008, 10:41 AM   #9 (permalink)
coony4w
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Like stated above a good bases is you need ten psi for every thousand rpms. If your running a synthetic it will be lower even at higher rpms. They say this is ok as it lubricates and bonds better then conventional oil. My 8.1 runs around the same pressure as yours when it gets close to it's oil change and I keep it on 10-30 penn. Haven't had any problems with it yet.
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Old 12-12-2008, 11:17 AM   #10 (permalink)
Tierod
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My truck has low presser too. I run 15w-40 oil in i to keep it up. I see 10 psi at idle with it. I'm also pushing 12 psi of boost on it with no problems yet.
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