Vehicle is a 2004 Escalade, 6.0 L with towing package. I purchased it with about 120K miles, now has 150K miles. Since I've had it, it's had regular oil changes with mobile 1, 5W or 10W only with mobile 1 filters. Last oil change was about 2 weeks ago.

Upon startup, oil pressure is about 15 PSI. Driving it averages about 1 PSI per 10 RPM (so about 20 PSI at 2000 RPM) but as the engine heats up, oil pressure drops slightly. So by the time you have been driving 10-20 minutes, when you stop at a light, engine idle is around 600 RPM and oil pressure drops just below 5 PSI. Warning light rings low oil pressure. Oil level is correct. There is no excessive valvetrain noise; the engine sounded fine so the first time it happened I gingerly drove it home (about 10 miles), carefully watching oil pressure gauge. Pressure was 10-20 PSI while driving home, dropped to about 4-5 PSI stopped at idle when I got stopped at two stop lights.

I replaced the oil pressure switch or sending unit with new AC Delco switch. Same results. I have HP Tuners, and the output from the sending unit matches that on the gauge cluster so I don't think it's gauge related.

Then I replaced the pickup tube 0-ring. Used Felpro, the one specific for the 6.0 L truck. My O-ring looked a bit deformed, so I thought this might solve the problem, but it didn't. Of possible note, there were a fair amount of iron shavings in the pan and on the magnetic drain plug. This is not usually the case during regular oil changes. Not sure if these are from my drive home, or whatever caused the initial loss of pressure. No sludge. Also cut open the 2 week old filter, and it was clean. Saw 1 or 2 very small iron shavings--these could have been from my cutting it open.

Then I removed the oil pump, hoping to find the oil pressure relief valve hung up. But, there is nothing obviously wrong with the oil pump, and the valve slides up and down the bore without too much trouble.

How can I evaluate the oil pump? Any ideas why I have low oil pressure? Is it reasonable to just purchase a new pump and bolt everything back together and just hope the problem has gone away without any specific evidence that I've found the problem?

Thanks in advance!!

 

I'm concerned about the iron filings you found.

I would suggest you get a mechanical pressure gauge and get it into the side galley seal. Then you can measure oil pressure at the pump. If it's "normal", there's a blockage in the galley leading to the oil pan ports and the barbell. This side galley seal is 16 x 1.5 straight thread.

If it's still low, maybe the barbell has an issue and oil is entering the rear cover. Pull the rear cover.

 

In for suggestions. I have a 03 2500 6.0L and it gives a low oil pressure warning on cold days. 167K mi, no start up noises out of the ordinary and will come up to 40psi when fairly warm and normal driving.

I have confirmed with a mechanical gauge placed at the OEM sending unit location that pressure is in fact "low" during initial 20seconds of start up then it will slowly rise.

I have actually put some THICK oil in for summer to alleviate this. But as this cold snap come upon us, the thicker oil is not helping...need to change back to regular weight oil.

OP, I have thought of doing the same about the pickup O-ring and to investigate the relief valve and even getting a new pump.

From what I have gathered, motors with high miles/worn bearings etc OR high performance motors set up with loose tolerances running thin oil can and would experience low "oil pressure". Pressure is a by-product of restriction in the system. So you could have "low pressure" but sufficient amounts of oil are lubricating key areas of the motor (someone correct me if I am wrong).

But IMO GM programmed the trucks to give a warning with anything under XX PSI, so I believe something may be going on.

 

I did some poking around:

I found this...http://www.jasperengines.com/pdf/GM60LOilPressureTB.pdf

Also that there has been some mention of a Lifter Valve Oil Filter which resides UNDER the Oil Pressure Sending Unit that can get clogged? That would be a cheap and easy check/replacement if in fact it is clogged up.

 

Thanks Paul and Smitty for the feedback/ideas.

I changed the oil pump, but have essentially the same issue. I put a mechanical gauge at the oil sending unit location, and see about 16 PSI at cold idle. After about 45 minutes of idle, pressure has dropped to 6 PSI at 600 RPM. Smitty, I had also found that technical bulletin that calls out the GM specification as a minimum of 6 PSI hot at 1,000. I have 10 PSI hot at 1,000 RPM, so that would seem OK. But when idling at a stoplight at 600 RPM, the low oil pressure warning light comes on and is pretty annoying.

I have not yet checked the oil pressure where you suggested Paul. I can also check it at the oil cooler inlet/outlet if I tap a spare fitting I picked up.

Smitty, I had heard the screen is only on 07 and up vehicles...I can barely see the top of the sensor with a mirror...not sure how the heck I could see down into the hole to find a screen! But if I see substantially higher pressure at the pump, that will be the next thing I look into.

I'll keep plugging away, but wanted to say thanks and update you guys. If you have any other ideas, please keep them coming.

thanks!
Paul

 

Paul, I can't even see the side galley plug without removing some stuff...front diff in the way. So I removed the lines for the oil cooler and measured pressure there. Same as at the sending unit, about 16 PSI on startup, and trending toward 6 PSI at hot idle (600 RPM). I think this is functionally the same as the side galley plug, right?

This makes me think it is not a screen under the sending unit issue. Either the pump isn't making pressure, or there is not enough resistance to the pressure downstream, so pump volume is there but no pressure.

The barbell forces oil into the filter and the cooler, correct? And also seals the high pressure line from the back cover?

I had the transmission worked on last year. I had them replace the rear main while the transmission was out. Maybe they didn't replace the barbell correctly? But why no warning bell until a year later? Any way to tell if it's the barbell without dropping the transmission?

Other ideas that fit my symptoms?

thanks!

Paul

 

Hey Paul, the barbell inside blocks the oil forcing it to go down into the pan, through the filter then it comes back up on the other side of the barbell block.

The barbell end that's flush with the back of the block blocks the oil from dumping in the rear cover forcing it up to the lifters.

 

The passages in the oil pan to and through the filter are tiny-like a 1/4 inch. And there's some tight turns. I hate it.

If there's any flashing, rubble, junk or anything blocking the pan passages, you'll get low pressure. You need to get a mechanical gauge on the galley running from the front to the barbell. This will take a reading before the pan/filter maze.

Here's where that plug is, it should be 16mm, the same as a LS1 OPSU.

 

Something that gets missed a lot is the rear cover and the can cover gaskets hold oil pressure and can loose oil pressure internally and be impossible to find. And with simply replacing those gaskets fix the problem. I've also seen bad pickup tube o rings and cracked pickup tubes. The screen is hard to see and get to. Patience a mirror flashlight and a o ring pick pull the screen out. I've seen it show low on the dash gauge and a mechanical guage. Replace screen and perfect again. The screen is only on engines with active fuel management.

 

Very true. If the rear cover seal was compromised or the bolts around the oil crossover section were loose, pressure across the entire oiling system could be lost to oil dumping into the rear cover.

If oil pressure is low before the oil pan, I'd pull the rear cover for a look.

 

These vehicles have been popping up in the local Pick Your Part type yards and we have noticed quite a few with spun cam bearings.

I have a neighbor that had the same issue with his 2500.

 

Take the pressure at the front oil galley plug. That way you only have pick up tube screen, pickup o ring and pump relief valve as possible issues.

Also what filter are you running? I had winter cold start issued in a 2500 HD 6.0l with 170K mi with a Fram filter (I know I know...I learned my lesson) and now it is a lot better with a Delco filter. I still only see 35psi cold idle where my 95 Z will see 40+ under same conditions.

 

If using thinner oil helps its most likely the pickup tube screen is partially blocked. I'll give you something to try that worked for me. I had slow oil pressure rise at start up, I started putting in 4ozs of ATF dex6 at every oil change. Now I get instant oil pressure readings AND the lifters got very quiet. I think the pickup tube screen had sludge built up in it. Car runs 100% better now too.

Also after using the ATF dex6 I noticed the oil turned jet black, so it cleaned up some kind of crap. I'm going to continue to use it every oil change long term. My car has 85k on it and I've always changed oil regularly but I bought the car with 36k and I don't think they did regular oil changes OR they let the dealer do it who knows?

 

You have a spun cam bearing time for a motor. It's usually the center one in the past couple of years we've changed probably 8 6.0s with the exact same failure pattern as yours and found cam bearings spun. I had a 06vmax that was my personal truck do the same thing just cruising down the highway. Theres no rhyme or reason doesn't matter how well you care or don't care for it it's just a problem those year models of motors had.

 

Ever find the issue or fix the problem?

 

I purchased a 150,000 mile 6.0 from a shop that I know. They replaced it with a newer unit. It had low oil pressure just like the O.P. I tore it apart and all of the bearings, crank and rod looked like brand new. Pulled the cam out and guess what? All of the top half of the bearings were showing solid copper.

 

wouldn't the pressure be the same here since the oil will flow to the least resistance worn parts etc. just asking

 

Welcome to LS1tech!

This spot is right after the oil pump before the filter and the small winding passages in & out of the filter. There will always be a pressure drop after the filter, more so if the filter has some mileage on it.

 

thank you for the fast reply, trying to help my son who has a 2003 sierra 6.0 , 165,000 miles pressure drops from 40psi when cold to 10 hot and sometimes so low the alarm goes off with no noises from engine , we just put some castrol 20w 50 and its better not much but keeps the alarm off ,sending unit is new and gauge cluster was rebuilt, tested with a mechanical gauge at oil filter housing using a "gearwrench" tool pressure confirms cluster gauge i'm old school and not into big repairs myself, so if i check pressure at the fitting near the oil pump you feel if its not the pump ,or oring or pickup tube/screen it should be reading normal psi there ?and if it is low it should be one of these . I look at water/plumbing as an example if i had a garden hose with a pressure gauge at the supply connection and another at the end of a lets say 10' hose it should read almost the same if i put a nozzle on the end to restrict the flow my pressure should go up but both gauges should read almost the same, i just don't want to go though the bs of changing the oil pump even with a mellings high pressure high volume for no reason thanks sorry for the long post lol

 

another question, if i have poor pressure due to bearings etc. and we change the pump to a high pressure/volume pump will this give the engine more time before a rebuild or exchange thanks again