Oil pressure dropping

[Musicars]

I'm still working on this low oil pressure issue on my '06 Denali. After several thousand miles I still have about 10 PSI of oil pressure at idle. Still no ticking or any other weird noise. I have been shopping around for a used lower mileage engine but would still like to figure out what is wrong with this one. It is just bugging me.

Had a thought. I was wondering if anyone knows if all of the oil passes through the oil cooler. In the only flow diagram I can find it appears to flow from the filter to the cooler and then back to the engine and up to the pressure sensor. There does not appear to be a bypass around the cooler. It that true?

I am exploring every possibility and was wondering what a restriction in the cooler could do.

 

[Chubbs]

Lubrication Description
Lubrication Description
Lubrication Flow Schematic




Click to Enlarge
Engine lubrication is supplied by a gerotor type oil pump assembly. The pump is mounted on the front of the engine block and driven directly by the crankshaft sprocket. The pump gears rotate and draw oil from the oil pan sump through a pick-up screen and pipe. The oil is pressurized as it passes through the pump and is sent through the engine block oil galleries. Contained within the oil pump assembly is a pressure relief valve that maintains oil pressure within a specified range. Pressurized oil is directed through the lower gallery to the full flow oil filter where harmful contaminants are removed. A bypass valve is incorporated into the oil pan, at the oil filter boss, which will permit oil flow in the event the filter becomes restricted. At the rear of the block, oil is then directed to the upper main oil galleries which are drilled just above the camshaft assembly. From there oil is then directed to the crankshaft and camshaft bearings. Oil that has entered the upper main oil galleries also pressurizes the valve lifter assemblies and is then pumped through the pushrods to lubricate the valve rocker arms and valve stems. Oil returning to the pan is directed by the crankshaft oil deflector. Oil pressure and crankcase level are each monitored by individual sensors.

An external oil cooler is available on certain applications, all 6.0L. Oil is directed from the oil pump, through the lower main oil gallery to the full flow oil filter. Oil is then directed through the oil pan outlet oil gallery, located in the left rear of the oil pan, and to the external oil cooler via a hose assembly. Oil flows through the oil cooler and returns to the engine at the oil pan inlet oil gallery, located in the left rear of the oil pan. Oil is then directed to the upper main oil galleries and the remainder of the engine assembly.

Oil Pump Assembly





Click to Enlarge
1 Driven Gear

2 Oil Pump Housing

3 Pressure Relief Valve

4 Pressure Relief Valve Spring

5 Plug

6 Drive Gear

7 Cover Bolt

8 Cover

 

[Musicars]

Thank you, That is kind of what I thought but I had only seen the flow diagram and did not have a description. I had been told by others that if I check pressure at the filter and it is lower than at the sensor port on top then it was a cam bearing issue. But it looks like the cam bearing and main bearings are on the same branch so I do not see how a pressure difference would indicate cam bearings. It is not like the mains get it first then it goes on to the cam.

It sounds like the only bypass is at the filter which would make me wonder if that bypass would be triggered or not if the cooler clogged since the cooler comes after the filter. Also, I wonder how much oil the bypass lets by. Would it be full pressure or just enough to keep the bearings from starving?

Anyway, I am looking at buying one of those spacers/adapters that goes between the engine and and oil cooler lines and check pressure there and comparing it to the sensor reading.

Maybe a long shot but I am curious as to where my pressure drop is.

 

[Rocket Man]

Thank you, That is kind of what I thought but I had only seen the flow diagram and did not have a description. I had been told by others that if I check pressure at the filter and it is lower than at the sensor port on top then it was a cam bearing issue. But it looks like the cam bearing and main bearings are on the same branch so I do not see how a pressure difference would indicate cam bearings. It is not like the mains get it first then it goes on to the cam.

It sounds like the only bypass is at the filter which would make me wonder if that bypass would be triggered or not if the cooler clogged since the cooler comes after the filter. Also, I wonder how much oil the bypass lets by. Would it be full pressure or just enough to keep the bearings from starving?

Anyway, I am looking at buying one of those spacers/adapters that goes between the engine and and oil cooler lines and check pressure there and comparing it to the sensor reading.

Maybe a long shot but I am curious as to where my pressure drop is.

There's a block off plate available for trucks without oil coolers. It might be possible to install it and just bypass the cooler to see if pressure increases.

 

[Musicars]

There's a block off plate available for trucks without oil coolers. It might be possible to install it and just bypass the cooler to see if pressure increases.

I considered that too and may go that route as it is cheaper. There are several versions. There is a plain block off, and one with tapped holes so I could put a pressure gauge on it. Then there are the ones that go between the the block and cooler lines that are tapped and those allow you to measure both in and out pressure. I suppose either route would tell me if the cooler is restricting. Cost is the biggest difference. Plain plates are $10 while the adapters run from $25 - $35 plus gaskets.

The idea of a restricted cooler is probably a long shot but I am trying everything to avoid yanking that engine out. Used motors with less than 150,000 miles are $1200 and up with installation at another $1200 if I don't do it myself, and unless I buy a whole running truck (which I do not have room for) I don't get to see it run and check pressures ahead of time.

 

[Musicars]

I installed a block off plate with a tapped hole so I could hook up a pressure gauge. The pressure was exactly the same at the port next to the filter as what shows on the dash gauge. It idles with 10 psi warm. Weird thing happened when I revved it up to 3,000 rpm. The pressure went to 40 psi but then I got a P0300 code. I cleared the code and it stayed gone.

At this point I can't think of anything else other than finding a replacement engine. The engine still runs great so I don't have to rush. I think I will keep this original engine and take it apart to see if I can find the problem. If I had the time and space I would probably take it out and fix it then reinstall. It stinks even more that this engine runs so well and does not have any of the noises I hear others have.

I have attached a pic of the block off plate installed.

 

[Musicars]

Thought I would give an update on my situation. It was suggested I send an oil sample to Blackstone Labs. I just got the results (the report went to the wrong email address at first). BTW, the oil pressure has remained low and not dropped any further and there are no new noises.

The report shows high iron (37), high lead (14), and high silicon (46). This was after 2,492 miles. The average should be 20, 5, and 10 respectively. I noticed Magnesium was high but some other things were low. They only highlighted the iron, lead, and silicon. Their comments as follows:

Indeed, we're seeing excess bearing wear in these results. Iron is from steel parts and lead is from the bearings. Together, they probably show excess wear at a bearing/shaft interface. Universal averages show typical wear after about 4,700 miles of oil use, so both metals should be lower after 2,492 miles. Silicon is high and may show abrasive dirt or harmless sealers from recent work. Check the air filter/intake for issues and listen for unusual noises. Continue to monitor oil pressure and use 2,500 miles or less until things improve. Check back to monitor wear levels.

Under the circumstances I guess I am not surprised. I don't know where the silicon came from. The air filter is clean and the only sealer I used (I assume they meant harmful, not harmless) was the dab you put where the front and rear covers hits the oil pan and that was not until the problems started but who knows what was done before. It was a quart and a half low when I got it and the oil was filthy.

I hate pulling out a motor that runs this well with no noises, no leaks, no other problems but I guess, one way or another, it has to be rebuilt or replaced. I better get back to looking for a replacement. Maybe I can rebuild this one for future use.

 

[swathdiver]

I hate pulling out a motor that runs this well with no noises, no leaks, no other problems but I guess, one way or another, it has to be rebuilt or replaced. I better get back to looking for a replacement. Maybe I can rebuild this one for future use.

You could probably put new rings and bearings in it and keep on truckin'.