Why does a UPF48r filter result in more engine oil pressure than a PF48e?

ZeeOSix

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I’m not certain, but what I’ve inferred is that the ECM knows what pressure to expect at certain conditions and when it is sufficiently outside of the expected value, the p0521 code triggers.

I’ve replaced the filter and screen twice - once in June and the second in November - each time with OEM. It seems unlikely to me that each of the new ones would have gone bad that fast.
It might be worth trying a new oil pressure sensor ... I don't think they cost much.

Did you also record and compare oil pressure with the mechanical gauge with different oil filters?
 
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I'm going to go out on a limb and assume this is a cylinder deactivation (AFM) engine. The engine oiling system on these is divided and regulated in two parts; the main oiling system, including crank mains, rods, and cam bearings are regulated at whatever the oil pump mechanical bypass is calibrated to. The AFM assembly under the intake, including the sensor, is regulated to 55-75 PSI by a separate mechanical regulator that screws into the oil pan. Symptoms when this second regulator goes bad usually are that oil pressure is fine cold, but as the engine warms up and the oil temp increases pressure continues to drop, eventually reaching the threshold at which the ECM sets the P0521 code. (It's around 15 PSI, can't remember for sure.) GM's test procedure to verify oil pressure actually includes 2 mechanical gauges; one in place of the oil filter and one in place of the sensor. Long story short, if you're checking pressure at the sensor with a mechanical gauge, you're not reading base engine oil pressure. Also, the different filter may contribute to differences in oil pressure readings, but in my experience likely isn't the root cause of your problem.
 

russellbailey

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It might be worth trying a new oil pressure sensor ... I don't think they cost much.

Did you also record and compare oil pressure with the mechanical gauge with different oil filters?
I misspoke - I meant that I replaced the sensor and screen twice.
 

ZeeOSix

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An oil filter shouldn't effect the oil pressure reading when the pressure sensor is located after the filter - as long as the pump in not in pressure relief. The PD oil pump is going to still put the same oil volume through the engine vs RPM regardless of the filter. The oil pressure is directly related to the oil volume flowing through the oiling system - higher the flow, higher the pressure when all other variables are held constant. And the filter's bypass valve has no effect on the engine oil pressure - the bypass valve operates independently, based only on the delta-p across the filter.
 

russellbailey

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I’ve got about a 500 mile drive today with the new filter during which I’ll gather more data. Below are the history data about p0521 on my car that I gave to the mechanic.

I’ve read about the pump o-ring potential problem and have not specifically tested for that. I’m going to keep gathering info and see what happens with this upf84r filter that GM recommends for this error code.
—————
Notes:
- Does use oil – 1 qt every 500-2000 miles
- Power has dropped in last couple of years – notable towing 7500 lb boat trailer up US220 from Greensboro
- No check engine light (CEL) ever until these p0521 codes started in June 2020

1. June 2020 – 1st p0521
a. 161,430 miles
b. CEL (check engine light) - P0521 error
c. Was pulling boat trailer on 220 N near Rocky Mount – engine working hard but have
done this route many times
d. Oil was about 0.75 qt low – still on a dipstick dot, added 1 qt
e. CEL turns off about 75 miles later
f. Local mechanic replaced oil pressure sensor and screen - did not blow out hole to my knowledge - screen was not clogged

2. November 2020 – 2nd p0521
a. No CEL in interim
b. 167,350 miles
c. Car had sat for 6 weeks after hitting a deer
d. Within 20 miles of around town easy driving after body repairs, CEL came on again – same p0521
e. Owner replaced sensor and screen - screen was not clogged
f. Owner also used compressed air to blow down the sensor hole and blew some bits of crud out into the
oil drain pan (hole connects to oil filter mount)

3. January 10, 2021 – 3rd p0521
a. 169,960 miles
b. Driving home from Snowshoe WV ( mountainous but no trailer), CEL came on after driving over some mountains –
again p0521
c. Oil about 0.5 qt low – two dots on dipstick were wet
d. Light smoke from dipstick port when dipstick pulled – common to see
e. Added oil
f. 170,020 miles and 2-3 days later – CEL light turns off

4. January 15, 2021 – 4th p0521
a. 170,100 miles
b. Towing 7500 lb trailer on US460 East towards Lynchburg
c. Oil level was full

5. January 18, 2021 – CEL light turns off – 170,715 miles
 

russellbailey

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Oil filter either has a lower bypass or free flowing media, or both

I would use the suspect filter with thicker oil and see what happens

Does the issue occur with aftermarket filters?
I’ve always used pf48e until yesterday when I swapped on the upf48r filter. . I’ve not tried any other filters. And I’ve been using the recommended Dexos spec and weight in a synthetic oil - I think it is 5w-30.
 

russellbailey

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I'm going to go out on a limb and assume this is a cylinder deactivation (AFM) engine. The engine oiling system on these is divided and regulated in two parts; the main oiling system, including crank mains, rods, and cam bearings are regulated at whatever the oil pump mechanical bypass is calibrated to. The AFM assembly under the intake, including the sensor, is regulated to 55-75 PSI by a separate mechanical regulator that screws into the oil pan. Symptoms when this second regulator goes bad usually are that oil pressure is fine cold, but as the engine warms up and the oil temp increases pressure continues to drop, eventually reaching the threshold at which the ECM sets the P0521 code. (It's around 15 PSI, can't remember for sure.) GM's test procedure to verify oil pressure actually includes 2 mechanical gauges; one in place of the oil filter and one in place of the sensor. Long story short, if you're checking pressure at the sensor with a mechanical gauge, you're not reading base engine oil pressure. Also, the different filter may contribute to differences in oil pressure readings, but in my experience likely isn't the root cause of your problem.
Yes, it does have AFM. That is interesting about the second regulator.

The mechanic who tested pressure only did it at the sensor location - I know he did not do it at the filter also.

I’m curious if you may know the answer - is the p0521 code triggered solely by the oil sensor at the top rear of the engine? Or does it also sense pressure somewhere else? My impression was the sole pressure reading location is that top rear oil sensor.

I agree that I don’t think the pf48e filter is the root cause of the problem, but somehow it appears that the upf48r filter acts as a band-aid of sorts to reduce the problem.
 

4WD

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I’ve always used pf48e until yesterday when I swapped on the upf48r filter. . I’ve not tried any other filters. And I’ve been using the recommended Dexos spec and weight in a synthetic oil - I think it is 5w-30.
I had a 2010 5.3L for 8 years… it saw various filters from AC Delco, Purolater, Fram, and Wix.
It ran various brands of 0w30, 5w30, 10w30, 5w40, and 15w40 …
Oil pressure was steady …
 
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I could be a combination of issues here. It's possible the OP has a leaking O ring and the system is sensitive to some light blockage in the oil filter. We have a lot of posts about LS engine O rings here. I'm trying to find one.
 
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4WD

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I’m not certain, but what I’ve inferred is that the ECM knows what pressure to expect at certain conditions and when it is sufficiently outside of the expected value, the p0521 code triggers.

I’ve replaced the sensor (had miswritten filter originally) and screen twice - once in June and the second in November - each time with OEM. It seems unlikely to me that each of the new ones would have gone bad that fast.
Snag: would that be done with the aforementioned screen ?
 

4WD

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I could be a combination of issues here. It's possible the OP has a leaking O ring and the system is sensitive to some light blockage in the oil filter. We have a lot of posts about LS engine O rings here. I'm trying to find one.
Yeah, was thinking Clinebarger would join in on that issue …
 
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Here is one of the links on the O ring issues. Also, I'd like to see the oil pressure at 60 mph now that the new filter is on.

 
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PD oil pump has pump slip. Any flow restriction after the pump can and will affect its ability to flow. Quit getting hung up thinking that a PD oil pump is something perfect because it isn't.

Lower bypass pressure, when all else is equal will reduce pump slip and load on pump, and could reduce pump bypass when reaching PSI limits.

I don't understand why some think that its OK to have an engine with blowby but refuse to accept "blowby" from an oil pump in relation to the flow restriction downstream from the pump.. I live in the real world and not in a textbook. Pump knowledge is definitely lacking in the world, along with filter expectations.

Higher PSI comes from less pump slip caused by the filter.

The OP can either use the fancy filter, or stick with the "failing" filter and adjust other variables. For example, if you go back to the CEL causing filter, skip the 5w30 dexos and use the 0w40 dexos and see if issue repeats. Thicker oil for a tired engine is nothing new.

0w40 + PF48E =
5w30 + UPF48r = GM solution... no CEL
5w30 + aftermarket filter =
5w30 + PF48E = CEL

So, get out there and start testing and post other issues/solutions.

If you use the 5w30 and PF48e and get the CEL, when low a pint, simply top off with STP synthetic(gold bottle) and see if the problem goes away.
 
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It’s true that restrictions will cause the oil pump on a LS engine to dump oil back in the pan even though it is a positive displacement pump. Here is a photo of a Melling oil pump showing the spring that is placed in the cylindrical section of the pump and regulates the oil pressure. This oil pressure is not actually measured, and instead, " oil pressure" is measured at the top of the engine near the fire wall. If it all works correctly the pump is creating enough flow to produce about 40 psi at the sensor at highway speeds but there is no feedback loop to tell the pump that.

LS Oil Pump.JPG
 
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Yes, it does have AFM. That is interesting about the second regulator.

The mechanic who tested pressure only did it at the sensor location - I know he did not do it at the filter also.

I’m curious if you may know the answer - is the p0521 code triggered solely by the oil sensor at the top rear of the engine? Or does it also sense pressure somewhere else? My impression was the sole pressure reading location is that top rear oil sensor.

I agree that I don’t think the pf48e filter is the root cause of the problem, but somehow it appears that the upf48r filter acts as a band-aid of sorts to reduce the problem.
It indeed only measures pressure at that one location. That's why GM tells you to check it in both places during diagnosis, as it's the only way to accurately see what each side of the system is doing. Pressure at the sensor should never be lower than pressure at the filter, if it is, then the AFM regulator is bad. If it's low in both places it's a base engine oiling problem.
 
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The mechanic was probably right. Oil pumps and engines do wear out, and faster when used hard. There are even lots of pictures of aftermarket oil pumps. They must be selling quite a few to keep making them. Your engine burns oil though and more when towing, so it probably is engine wear. But the new filter helped so you have more miles of engine life ahead.
 

ZeeOSix

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PD oil pump has pump slip. Any flow restriction after the pump can and will affect its ability to flow. Quit getting hung up thinking that a PD oil pump is something perfect because it isn't.
Sure PD oil pumps have some "pump slip" (ie, not 100% perfect at moving 100% their volume per RPM), but on a healthy pump it's not much and won't cause any problems. Pump slip gets worse as the engine RPM increases and the pump has to put out higher and higher output pressure. But IF the pump is in good health then it shouldn't be effected under any operating conditions by using different oil filters that probably only have a couple of PSI delta-p difference between them. If that was the case, there would be thousands of vehicles on the road that would have issues with different oil filters. If the filter became totally clogged, and the bypass valve opened and wasn't large enough to flow all the oil, then it could push the pump into pressure relief. But that isn't even close to what's going on with the OPs vehicle. I don't recall him saying he cut open any used oil filters, but it might be a good idea. And it sounds like it happens with filters with not many miles on them.

Lower bypass pressure, when all else is equal will reduce pump slip and load on pump, and could reduce pump bypass when reaching PSI limits.
The oil filter bypass valve isn't going to open until there is a lot of delta-p across the filter. Most engines won't even hit pump pressure relief near redline RPM when the oil if fully hot - it takes a huge GPM of hot oil flow to make a typical filter bypass valve to open when the filter is new. The OP isn't seeing this issue anywhere close to engine redline.

If it's cause by "pump slip", then his oil pump is too worn out to supply enough oil volume and pressure to the oiling system. But he has checked the oil pressure with a mechanical gauge and it seemed pretty close to normal. Maybe the pressure relief valve on the pump is flaking out if the pressure is erratic.
 
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russellbailey

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Here is one of the links on the O ring issues. Also, I'd like to see the oil pressure at 60 mph now that the new filter is on.

Driving tonight at about 60 mph - was slightly rolling terrain. This is a about 750 miles after the oil change and is clearly higher than with the pf48e filter.

The graph of oil pressure is for a 2-minute time period.
 

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