Lower oil pressure mid OCI, PF48

[HawkeyeScott]

2008 Suburban with 5.3, 161K. Changed oil in November and used AC Delco PF48 filter and Napa 5W-30 full synthetic. Have about 1800 miles on the oil change at this point.

Late this week, I noticed somewhat lower oil pressure on the gauge and more fluctuation than usual. Maybe a little slower to build pressure on cold startup (in 45 degree garage), but really noticed it running about 15 PSI lower throughout my commute. High PSI wasn't as high and low PSI was lower than normal. Never alarming - it always stayed in the spec range - but certainly made me curious since I've never seen this before on this truck in 50K+ miles of ownership over 7 years.

So, I bought a ST10060 yesterday, prefilled it and installed on the truck in place of the PF48. I've only started and driven it once, but it appears the oil pressure is now back to normal.

I just cut the PF48 open and nothing appears out of the ordinary. Media is good, no crud/carbon/sludge to speak of. ADV looks good. To the eye, the filter looks healthy.

I know there are some threads about oil pressure diminishing mid OCI on some 5.3 motors and it is remedied by a new filter.

I will continue to monitor this week. But if this was, in fact, the filter but the filter looks good, any idea what was going on?

 

[BrendanC]

one major thing on these LS motors is the oil pump pickup O ring. it gets brittle over time and will crack allowing for the pump to suck air when it’s hot. i’ve replaced dozens of them.

 

[oldhp]

Doesn't make sense. But a new oil filter + 10ozs ( ? ) new oil fixed your problem. Maybe next oil change try a full synthetic oil filter. Royal Purple has full synthetic oil filters. Should be Royal Purple #10-48.

 

[twX]

You won't necessarily be able to tell if a filter is clogged just by looking at it. Filters clogged by dust during a capacity test still look like new when cut open. That said, it would be really unusual for a filter to clog in 1,800 miles. Maybe that filter was highly restrictive when new.

 

[twX]

Maybe next oil change try a full synthetic oil filter. Royal Purple has full synthetic oil filters. Should be Royal Purple #10-48.

A Royal Purple filter was the most restrictive filter tested by Ascent Filtration a few years ago.

For a filter with low restriction, I'd use a Purolator BOSS, PurolatorOne, Mobil 1, Wix XP, or NAPA Platinum, which have all done well in the dP tests I've seen. The Supertech that's on the engine right now is very similar to the PurolatorOne and Mobil 1, so I'd expect it to have low restriction as well.

 

[BrendanC]

A Royal Purple filter was the most restrictive filter tested by Ascent Filtration a few years ago.

For a filter with low restriction, I'd use a Purolator BOSS, PurolatorOne, Mobil 1, Wix XP, or NAPA Platinum, which have all done well in the dP tests I've seen. The Supertech that's on the engine right now is very similar to the PurolatorOne and Mobil 1, so I'd expect it to have low restriction as well.

the difference in Dp in that test were almost negligible. none of the oil filters that are specified for this application will have any noticeable difference in flow unless you get into a racing can.

 

[ZeeOSix]

For oil pressure to drop (assuming the oil pressure sensor is located after the filter) due to a more restrictive oil filter, the pump would have to be in very bad condition (ie, it slips like mad due to being excessively worn out), and/or the pump would have to be in pressure relief, which could also happen due to the pressure relief valve malfunctioning.

 

[ZeeOSix]

the difference in Dp in that test were almost negligible. none of the oil filters that are specified for this application will have any noticeable difference in flow unless you get into a racing can.

Yeah, a few PSI difference in dP due to an oil filter isn't going to make any healthy PD oil pump hit pressure relief (especially at low RPM) or make the pump slip so bad that oil flow is drastically cut back. If the pump was extremely worn out, maybe. A cut-back in oil flow would be indicated by lower pressure if the sensor is located after the filter.

 

[ZeeOSix]

A Royal Purple filter was the most restrictive filter tested by Ascent Filtration a few years ago.

For a filter with low restriction, I'd use a Purolator BOSS, PurolatorOne, Mobil 1, Wix XP, or NAPA Platinum, which have all done well in the dP tests I've seen. The Supertech that's on the engine right now is very similar to the PurolatorOne and Mobil 1, so I'd expect it to have low restriction as well.

At 40 L/min flow (10.6 GPM), there was only 4.5 PSI difference in dP between the least restrictive filter (Wix XP) to the most restrictive filter (Royal Purple). At much lower flow (ie, lower engine RPM), the difference in dP will be very small between all those filters that Ascent tested. That difference in dP isn't going to really matter to a healthy PD pump.

If for some reason, the filter was totally clogged from debris and the filter was flowing almost all the oil through its bypass valve (typically not really sized for full bypass flow), then a condition like that could put a lot more dP back pressure on the pump and cause it to slip way more if worn badly, and/or put the pump in pressure relief. But it seems really unlikely this filter was near being total clogged unless this engine is a big sludgier or the OP was doing some kind of cleaning process that loaded up the filter badly.

 

[jhellwig]

Oil pressure sensor problems are an issue on these.

 

[ZeeOSix]

Oil pressure sensor problems are an issue on these.

Yes, seems to always be on this engine - and half way through an OCI. If a few PSI difference in filter dP effect was a real impact on oil pressure, it would be reported on many other vehicles. But it's not.

 

[HawkeyeScott]

Oil pressure sensor problems are an issue on these.

I had an issue with zero pressure immediately after an oil change last year. Ended up installing a new OEM sensor to rectify. Everything was normal on the oil pressure front for 7500 miles until I noticed the changes mentioned above this past week. Hopefully the new sensor is still good.

 

[350Rocket]

I remember seeing this behaviour on my truck years ago (before it was mine). It was my company supplied work truck and got cheap conventional oil changes at a local place every 3k miles. Around 2k miles the oil pressure on the factory gauge would drop from the usual 40 psi at idle to something around 30 or less. It would always return after an oil change but was always a mystery to me. At some point before I bought it but after I became the sole driver, I started doing the oil changes myself... buying full synthetic and a fram ultra on sale and getting reimbursed and I stopped noticing the problem. It was likely the cheap Ecoguard filters it was getting. The oil pressure sending unit kept working for years after that and when it failed it just went from normal to well over 100psi randomly until it stayed there permanently.

 

[A_User55555]

I think the e-core filters can be a bit restrictive. On my old 1999 Deville 10 years ago, I installed a PF-61E filter. After 1000 miles, the oil light would flicker at idle sometimes

After that I only used the original AC Delco PF-61 and the oil light never came back on the rest of the time I had the car

However on my 2011 DTS, I tried using the PF-61E filter again and had no problems

 

[GMBoy]

I had the same issue with AC DELCO filters on 3 different occasions where at start up was zero pressure on a hot restart. Each time replacing the filter fixed it. There was nothing wrong with the truck. I stopped using them and every other oil filter I used since did not do it.

 

[ZeeOSix]

I think the e-core filters can be a bit restrictive.

How so, why? An eCore center tube will produce a hair less dP (like less than 0.5-1 psi less) than other center tube designs. But regardless, oil filter center tubes are low dP producers anyway regardless of their design, unless it's a louvered center tube with very choked down louvers. The media is by far the most restrictive part of any oil filter. And even then, the dP across a whole oil filter assembly is very small compared to the flow restriction of the engine oiling system - especially at idle with hot oil. These engines that supposedly lose oil pressure due to an oil filter must have borderline PD oil pumps, and/or the filters are getting near totally clogged up during use and putting the pump into pressure relief.

 

[Brian123]

redhat​

JoinedDec 7, 2012Messages3,359

• Jan 27, 2023
• 
  
• Add bookmark
• #12

The usual symptoms of an O-Ring that needs replacement is low oil pressure upon startup (20-30 PSI) and an oil pressure reading that DOES NOT increase much with RPM until the engine is warmed up. The failure that occurs is that the O-Ring gets hard and shrinks over time. With some heat in the engine/oil, the O-Ring swells back up and your pressure starts to look normal.

I know, I know, they say 8psi per 1,000 RPM on small-block Chevy's... but any Gen III LS I've ever driven, with a half-way decent shape motor has been 40-45+ PSI on cold start and 35/38-40 PSI at hot idle on a 5W-30. Maybe a little bit more on 15W-40. Gen III do not normally sit at 15-20-25 PSI.

Also, yes the oil pressure gauges are not NASA exact and do have some (maybe a lot) of margin for error, however, you get used to what they should look like regardless of their accuracy.

Drop the Oil Pan and check your O-Ring, this is not an Oil Filter issue.

 

[mt23]

Have a 2006 Express with the 4.8L that I will be dropping the pan to replace O ring and inspect pickup tube that does exactly the same thing. 20 psi cold oil pressure startup which will dip lower with more rpm. (Lifters will start clacking if driven too much, cold) and then 35psi idle builds up to 55 psi with rpm once oil is heated up fully. Halfway through oil change the hot oil pressure drops about 5psi and replacing the oil filter raises it back 5psi. Always carbon in filters on this 4.8 but I dont think it's a restriction issue as it isnt excessive carbon

 

[350Rocket]

How so, why? An eCore center tube will produce a hair less dP (like less than 0.5-1 psi less) than other center tube designs. But regardless, oil filter center tubes are low dP producers anyway regardless of their design, unless it's a louvered center tube with very choked down louvers. The media is by far the most restrictive part of any oil filter. And even then, the dP across a whole oil filter assembly is very small compared to the flow restriction of the engine oiling system - especially at idle with hot oil. These engines that supposedly lose oil pressure due to an oil filter must have borderline PD oil pumps, and/or the filters are getting near totally clogged up during use and putting the pump into pressure relief.

I think his comment was based on the personal experience he had as posted...but sounds like it was only one oil filter, so possibly a defect?

redhat​

JoinedDec 7, 2012Messages3,359

• Jan 27, 2023
• 
  
• Add bookmark
• #12

The usual symptoms of an O-Ring that needs replacement is low oil pressure upon startup (20-30 PSI) and an oil pressure reading that DOES NOT increase much with RPM until the engine is warmed up. The failure that occurs is that the O-Ring gets hard and shrinks over time. With some heat in the engine/oil, the O-Ring swells back up and your pressure starts to look normal.

I know, I know, they say 8psi per 1,000 RPM on small-block Chevy's... but any Gen III LS I've ever driven, with a half-way decent shape motor has been 40-45+ PSI on cold start and 35/38-40 PSI at hot idle on a 5W-30. Maybe a little bit more on 15W-40. Gen III do not normally sit at 15-20-25 PSI.

Also, yes the oil pressure gauges are not NASA exact and do have some (maybe a lot) of margin for error, however, you get used to what they should look like regardless of their accuracy.

Drop the Oil Pan and check your O-Ring, this is not an Oil Filter issue.

I am one of the people who has seen this oil pressure drop...but it was several years ago and around 170k miles (currently at 255k miles) and my oil pressure hits around 50 psi within a few seconds of cold start. It will also climb to over 60 at high RPM once warmed up but has last about 10 psi over the years for hot idle. Down from 40 to 30 although that includes a new oil pressure sending unit after it being broken almost a year. It was down to 32-34psi with the factory sender before jumping to 135 psi and being non functional for a year.

Doesn't sound like a bad o ring in this case right?

 

[ZeeOSix]

I think his comment was based on the personal experience he had as posted...but sounds like it was only one oil filter, so possibly a defect?

What I'm saying is that his theory that it was because the filter had an eCore center tube is off base. Like mentioned, the only time an oil filter could cause an oil pressure drop on a sensor located after the filter is if the filter was so clogged that it was causing an unhealthy worn oil pump to slip like mad, and/or cause the pump to hit pressure relief. A healthy PD oil pump will literally destroy something in the oiling system if it wasn't pressure regulated by its pressure relief valve.