8.1 Oil Pressure and Filter

[BurbMan]

Last oil change I installed a Fram Ultra Guard since the Wal-Mart by me stopped carrying AC Delco filters. Local auto parts stores don't seem to carry the AC Delco filters either. Right after that I ordered some OEM PF-454 filters from Rock Auto so now I have a few on hand.

On a road trip to Chicago last week I noticed that the oil pressure was lower than normal....it was only running about 20 psi at idle and about 45 psi at 2500 RPM. I did an oil change yesterday with a little over 5k miles on the oil, and today I see the oil pressure is running about 10 psi higher, 30 psi at idle at about 55 psi at 2500 RPM with the AC Delco filter installed. This is where the oil pressure always was on this truck, so I consider this to be normal, so the oil pressure was running about 10 psi lower overall with the Fram filter.

The oil I am using is Mobil-1 5W30 Hi-Mileage formula.

I'm not sure if this is a function of having 5k miles on the filter or if the Fram filter is too restrictive vs. OEM. I never recall seeing a drop in oil pressure over the life of an oil filter. Does that mean the Fram is filtering better?

As an aside, I changed to synthetic at about 100k miles (160k on the truck now) and have noticed about 1 mpg improvement and I no longer get the infamous "piston slap" at startup...much quieter now. For the first 100k miles, I used regular dino oil with a 3k change interval, now I go 5k with synthetic.

Who makes the best oil filter these days anyway? The AC Delco's online were only $3.40 each, the Fram was $8+ at wally world, and I see they now have Bosch filters at $10+. Tempting to think that the more expensive filter is better, but as with anything else, that's more often marketing than actual quality.

I also did another Blackstone sample, and will post results when it comes back.

[GeoBoy]

K&N oil filters are all about filtration and FLOW. Chevrolet engines are about flow and not necessarily high oil pressure.

[Devocamper]

BurbMan wrote:
Last oil change I installed a Fram Ultra Guard since the Wal-Mart by me stopped carrying AC Delco filters. Local auto parts stores don't seem to carry the AC Delco filters either. Right after that I ordered some OEM PF-454 filters from Rock Auto so now I have a few on hand.

On a road trip to Chicago last week I noticed that the oil pressure was lower than normal....it was only running about 20 psi at idle and about 45 psi at 2500 RPM. I did an oil change yesterday with a little over 5k miles on the oil, and today I see the oil pressure is running about 10 psi higher, 30 psi at idle at about 55 psi at 2500 RPM with the AC Delco filter installed. This is where the oil pressure always was on this truck, so I consider this to be normal, so the oil pressure was running about 10 psi lower overall with the Fram filter.

The oil I am using is Mobil-1 5W30 Hi-Mileage formula.

I'm not sure if this is a function of having 5k miles on the filter or if the Fram filter is too restrictive vs. OEM. I never recall seeing a drop in oil pressure over the life of an oil filter. Does that mean the Fram is filtering better?

As an aside, I changed to synthetic at about 100k miles (160k on the truck now) and have noticed about 1 mpg improvement and I no longer get the infamous "piston slap" at startup...much quieter now. For the first 100k miles, I used regular dino oil with a 3k change interval, now I go 5k with synthetic.

Who makes the best oil filter these days anyway? The AC Delco's online were only $3.40 each, the Fram was $8+ at wally world, and I see they now have Bosch filters at $10+. Tempting to think that the more expensive filter is better, but as with anything else, that's more often marketing than actual quality.

I also did another Blackstone sample, and will post results when it comes back.

I used to use K&N oil filters on my 8.1 chevy and they seemed to work well, not sure if they are the best but they say they are . If your interested I have 4 or 5 left over (new in the box) from when I changed trucks PM me if you would like to learn more.

[ib516]

I did an experiment on oil filters a while ago. FRAM was included.

Here's a link OIL FILTER AUTOPSY

[AH64ID]

BurbMan wrote:
AH641, thanks for posting that, and making me feel lazy for not digging the service manual out of the garage and looking it up myself. But given that the 8.1 is not referenced tells me it may be different. I'll see if I can find it in my Helms manual and post.

It took a marine 8.1L mechanical service manual but I found it. There is a flow diagram with it, that looks very similar to what was already posted.

The oil is drawn from the oil pan through a pickup screen and tube, into the oil pump (7). Pressurized oil flows through the oil filter, into the oil cooler (5), back into the engine (6), up to the oil pressure gauge port (2) and rear crankshaft bearing, and is then distributed to the upper oil galleries.


I also found several sources that show min pressure as 5 at 1,000 and 10 at 2,000. I found a different min rating (2 ratings 1 manual) that says 6 at 1,000, 18 at 2,900 and 24 at 4,000.

[BurbMan]

AH641, thanks for posting that, and making me feel lazy for not digging the service manual out of the garage and looking it up myself. But given that the 8.1 is not referenced tells me it may be different. I'll see if I can find it in my Helms manual and post.

[GeoBoy]

You couldn't pay me to run Fram filters. I run Amsoil, K&N or OEM oil filters only.

[marquette]

hawkeye08 is correct. I meant flat tappet and roller cams. push rod was a bit of a generalization.

[BenK]

Don...old habits die hard... :B

Will continue to HEET my tank before each test...if I remember and why
I know mine all pass way below the average 'car' in the state. Bugs
me that they label all of my vehicles as 'high emitter profile'...so
gotta get my readings down LOW

As for the loss of the traditional lube additives...have been using
Molybdenum Disulphide since the 60's when designing stuff for military
contracts

Found a consistent reference to MolyB and searched out their #1 source.
Called them and found in Calif and bought through our PO with a line
item for my personal use

It is now common in lots of oils from their factory. Continue to use
and almost gone my one and last time buy from them when they closed

Now testing Tungsten Disulphide and see similar results. Mainly with
small displacement. Runs cooler is the key indicator for me.



Part of my stock and even my grease gun is loaded with MolyB filled
MolyB Molybdenum


MolyB Molybdenum


This is from my first buy back in the 60's....found this can after the
divorce and moving

[hawkeye-08]

marquette wrote:
At one time I did a lot of reading about oil and filers on the Bob The Oil Guy forum. After reading about Fram filters (that I has been using) I switched to the NAPA Gold filter. It didn't raise my oil pressure as much as it did hold my oil pressure at it's high range. Meaning when I come to a stop or slow down the oil pressure doesn't drop the way it did with the Fram filter. From what I understood it has something to do with better back flow valves in better filters. The NAPA Gold is not unique to that it's just readily available for me. I also learned that it is important to match your oil to your engine. Push rod engines need different oil that roller cam engines. For example my old 4.0 Jeep push rod engine needs more zinc for wear than synthetic oil provides but a 4.7 Jeep will do better with synthetic because of the cam design. Much like this forum there is a lot to learn over on the oil forum if interested.

I think what you meant with push rod engines is actually flat tappet (lifters) vs the roller lifters. The new oils have the zinc and phosphates removed for better emissions and you either need to use additives or special oil that is meant for flat tappet engines (such as my 454 in my 73 Chev). You can have push rods with flat tappets or roller cams.

[AH64ID]

Looking at where the filter is located, and where the sender is located it is most certainly post-filter. There is not one single reason to internally flow unfiltered oil up to the valley and back down to the filter, just to measure pressure pre-filter. Pre-filter and bypass pressure is really useless anyhow, it can potentially be very misleading to actual oil pressure, since a plugging filter will show high pressure and decrease pressure to the engine.

This is a SBC diagram, but how the 8.1L probably is plumbed as well. You can see the oil pressure sending unit in the top right of the diagram, post-filter.

[gijoecam]

Think of pressure as the resistance to flow. No resistance to flow (i.e. an open garden hose) = 0 pressure. High resistance to flow (a crimped garden hose) = high pressure.

The key is: Where is the pressure measured? Up-stream or downstream of the filter? My guess is that, since the Fram ran at a lower pressure, the pressure sensor on your engine is upstream of the filter. (Fram generally flows more oil, hence less restriction and lower pressure). Low pressure doesn't necessarily mean low flow or a bad oil pump. It may simply mean that the filter flows more oil.

At work, we measure pressure drop across the filter to determine when it's clogged and in need of a change. Engineers far more skilled than I am did the calculations and have determined that at XX GPM flow rate, the pressure drop across a new filter should be XX psi, when it's 75% clogged, it will be YYpsi, and when the filter is 'clogged' the pressure differential should be ZZ psi. Note that under all these conditions, the same amount of oil is actually flowing through the system.

It's a little tougher to make that sort of determination on an engine though... The flow is constantly changing with engine RPM and load. If your pressure gauge always shows the same pressure regardless of RPM (and I know the OP's doesn't but many do) it's not truly measuring the pressure.

[marquette]

At one time I did a lot of reading about oil and filers on the Bob The Oil Guy forum. After reading about Fram filters (that I has been using) I switched to the NAPA Gold filter. It didn't raise my oil pressure as much as it did hold my oil pressure at it's high range. Meaning when I come to a stop or slow down the oil pressure doesn't drop the way it did with the Fram filter. From what I understood it has something to do with better back flow valves in better filters. The NAPA Gold is not unique to that it's just readily available for me. I also learned that it is important to match your oil to your engine. Push rod engines need different oil that roller cam engines. For example my old 4.0 Jeep push rod engine needs more zinc for wear than synthetic oil provides but a 4.7 Jeep will do better with synthetic because of the cam design. Much like this forum there is a lot to learn over on the oil forum if interested.

[AH64ID]

BurbMan wrote:
The oil pressure sending unit on the 8.1 is on the back of the block just below the intake manifold. The oil filter hangs off the left side of the block lower down.

In this pic you can see the oil filter:

That's going to be post filter.

[BurbMan]

The oil pressure sending unit on the 8.1 is on the back of the block just below the intake manifold. The oil filter hangs off the left side of the block lower down.

In this pic you can see the oil filter: