lly low oil pressure

[AndyG]

Funny thing happened to me on the way home on the day before yesterday. Just cruising along as usual and heard the dreading ding ding ding, low oil pressure!!! Watched it for a second and the pressure came back up some then down. Up, then down, then as I pulled over it went to almost zero. I shut it down and checked the oil level. Seemed a little high. Let it cool off and decided I could go the 2 miles left to the house if it had some pressure. Fired it back up, pressure was lower than I thought it should be, but I had never payed THAT close attention to it.
The next day I drained about 1.5 quarts of oil from the crankcase (to about halfway on the dipstick) and did a spot test on some paper (inconclusive), no unusual smell in the oil, it didn't seem thinned out as if it had fuel in it. I disconneced the edge and boost stick and fired it up. Oil pressure runs just short of 60# when cold and as it heated up it dropped to just shy of 30# at idle when at normal temp. Drove it to town and it stayed just shy of 30# at idle and ramps up with rpms to about 60# at 2000rpm.
I am using Mobil 1 turbo diesel truck 5W-40 with a bypass filter, I have only about 3000 miles since I put the mobil 1 in. I plan to send a sample off for analysis.
Soooo, what is your question you may be asking...

Are these oil pressures normal?
Why did I get the low indications to begin with?
Could my edge have caused erroneous gauge readings?
Where did the extra oil come from?
Anyway I can know if the zero pressure was real?
Anyway I can know if the enging was damaged without disassembly?

Thank y'all for your help.

[DmaxMaverick]

Assuming you don't have a gage/sender issue, the conditions you experienced do not appear to be normal. Add that to the additional oil, and something is certainly wrong. If you have warranty, get it to the dealer.

Although rare, there have been reports of the HP fuel pump shaft seal failing, causing fuel to enter the crankcase. It will be covered by the 5/100 engine warranty, or your emmissions warranty, which vary state to state. If you are out of warranty, a fuel pump replacement isn't so bad if you do it yourself.

[AndyG]

Ok, so how much oil should I have expected to drain to go from the Full mark to halfway on the dipstick? (I suppose I should just go see how much from 1/2 to full). I might have overfilled to begin with, but I put 9.5 qts in for the oil change and part of that went into the filter before I spun it on.
The oil pressure has been ok for the last few days...so I reconnected the edge to see what happens. The ambient air temps around here have been a good bit lower these last few days, maybe the edge got hot and went snakey on me?

[DmaxMaverick]

Your crankcase is 10 qts. Drain it well, change the filter, and poor in 10 qts. Run it up to temp. and check your level, whichever way you normally do. That will be your benchmark for your oil level. Oil levels vary on the dipstick, but the sump is always the same size. You can't go by a "given" mark on the dipstick, so you need to set the mark.

Regardless of what you found/find, your situation still doesn't sound right.

[AndyG]

OK. drained and refilled. Only got 9 quarts in before the high mark on the dipstick and stopped there. Have to drive several hundred miles this weekend so we will see what happens. Unfortunately I didn't have Mobil 1 turbo diesel truck for the refill because nobody around here carries it...so in went the Delo dinosaur oil. I was trying to put in the good stuff and go with extended drain intervals, oh well.

[Kennedy]

Is there anything in your bypass plumbing that could restrict or dump too easily?

Another thought since it cycled is possibly a loose pickup. The pickup goes deep into the pan so you'd have to be WAY low for it to get air down low.

Then it could simply be a transducer or databus issue/erroneous reading...

[AndyG]

OK. I drove to Savannah, GA and back detouring through Aiken, SC. Approx 700 miles total and running from 55 to 75 mph almost the whole trip. Oil level stayed constant. Truck ran great. I even got 400 miles on one fill up (my truck seems to like B20 soy fuel!). Since that trip I've put about another 400 miles on it including one 8 mile trip off roading. No level changes, no oil pressure strangeness. Hmm. I think I will chalk it up to some computer glitch and continue to watch it.

[Mark Rinker]

My LLY oil pressure gauge reads much lower than the LB7s. Never had a zero reading, or alarm event, but a dealer looked at it, took a test of the pressure under the hood, and declared everything healthy.

Supposedly there is a TSB available on the topic for 2005 LLY trucks where customers are seeing <30lbs and bring the trucks in for service. GM states that 14psi (!!!) is the lowest acceptable operating oil pressure.

[68Nova]

On my new LBZ 07 with about 450 miles on it, took a highway cruise today and at 70 MPH it had about 50-55 (converted from kilopascals damn Canadian guages) psi oil pressure. This is reving only at about 1700 rpm. At idle it goes to about 30 psi. When I rev it over 2000 rpm it goes over 60 psi. I can understand that the oil pressure might be a concern because at highway speeds the oil pressure guage is below the half way point on the guage. How is other vehicles oil pressure at highway speeds in comparison? Is the guage showing under or over the halfway point at normal highway speeds?

[Mark Rinker]

Sounds about the same as my '05. Wait until a HOT day next summer, towing, with A/C on and you'll see what we are referring to. At idle, your needle will sit two or three needle widths from the low pressure 'red zone'. Well below 30psi. Enough to make you wonder...

[DmaxMaverick]

A minimum of 14 PSI is absolutely OK for the engine, according to GM. But at what RPM? I agree at idle, but at cruising RPM? The old standard was 10 PSI for every 1000 RPM. Like I said, the "old standard". Newer Diesel engines may be more or less tollerant of lower pressure.

That being said, that is NOT the problem. The problem is, the pressure dropped by 50% very quickly, without any changes to the oil components, fluid, or environment. Something happened to cause that, and THAT is what they should be diagnosing. NOT the acceptable oil pressures.

The high pressure relief for an LB7 is 64 PSI. I'm not sure what it is for the LLY, but should be similar. Could be the relief was "bumped", and it stuck open. That is where the dealer should start looking, along with the sender and gage. If all is normal now, keep a close eye on things. If it were the relief valve sticking open, it may happen again. Problem is, you (and the dealer) will have to catch it while it's happening.

My wife cooked a Mercedes 300D because of a failed oil pressure relief valve. Long and anecdotal story, but she waited 3 weeks before telling me the oil pressure gage wasn't working anymore, but the ECT was higher than normal (that gage must be broken, too). Synthetic oil kept the thing together for 3 weeks with just a dribble of oil flow.