My oil pressure is suddenly lower than usual

[cheesepuffs]

Hey guys. Background story: 1992 Chevy 5.0/305 TBI here. Previous OCIs by former owner were using whatever oil our local mechanics offer for cheap, i.e. CAM2 and other discount brand oils, except for the last previous oil that was Valvoline dino. There is noticeable sludge at least on the top-end when looking through the oil-filler cap/valve cover. I switched to PYB last week. Also, truck is a 5 speed manual.

My oil pressure for months since I got this truck has always been 30 psi. Start it up, it rises to 30, and maybe rises to 33 during driving/RPM increase, consistently. Yesterday night I noticed that at idle my oil pressure was dropping to about 16 psi, which is strange for this truck. Even when coasting downhill it was dropping from 30 to 16 as well. I have to tap the throttle (either at idle or while moving) to get the pressure to spike to 30 again, but then it drops back after a few seconds. Is that normal? Again, this truck has always held 30 psi regardless before last night.

Also last night I needed gas and went to Cumberland Farms instead of Mobil like I usually do. I noticed at the same time as my oil pressure issue that my truck was idling significantly rougher than usual. Idles with a vibration now similar to when a coil-pack fails. Bad gas? Maybe water contamination?

I had checked the oil yesterday too (it is completely full and no burning, leaking, or consumption issues here) and noticed that even after not even a whole week the oil is getting dirtier. Which means that it's doing it's job and dispersing contaminants and sludge - good. Could this Pennzoil already be removing some blockage in an oil passage or something thus causing my oil pressure fluctuation? Maybe this was just how it's actually supposed to be all along. Or maybe this seemingly bad gas is causing this rough idle, thus my idle isn't strong enough to keep the oil pump running fast enough to keep up?

Or maybe it's something completely different. Does anybody have any insight on this? I wanna hear any and all opinions because it seems really weird and sudden of a change for this vehicle.

Edit: Also I just thought of this... Could it be that my truck just got it's first dose of higher ethanol winter gas and just doesn't like it? It's an old engine after all, not really designed for that.

 

[nitehawk55]

You might want to have a look at your oil filter or just change it .

 

[cheesepuffs]

Originally Posted By: nitehawk55
You might want to have a look at your oil filter or just change it .


Interesting you say that because I had no idea what an ecore filter was until I bought it. Figured ACDelco would be fine (good enough for GM, good enough for me) but then I read how awful they are... Ugh, I wonder if this thing could have collapsed already.

 

[FL_Rob]

I think the PYB started to clean out the oil sender port allowing a better read.On my F150 (4.9),i took a real o/p gauge reading at the sender port..52 psi @idle.Upon cleaning the sender, the factory dummy gauge actually went a little higher not that it matters since i don't go by that anyway.

On the Chevy van with active gauge ,i can see the difference in
*cold start/hot start
*fresh oil vs sheared oil at the end of an oci
*idle fluctuation ..etc

 

[cheesepuffs]

Originally Posted By: FL_Rob
I think the PYB started to clean out the oil sender port allowing a better read.On my F150 (4.9),i took a real o/p gauge reading at the sender port..52 psi @idle.Upon cleaning the sender, the factory dummy gauge actually went a little higher not that it matters since i don't go by that anyway.

On the Chevy van with active gauge ,i can see the difference in
*cold start/hot start
*fresh oil vs sheared oil at the end of an oci
*idle fluctuation ..etc


I didn't think of that. Was actually thinking that maybe the sender came a little loose somehow. But you have a good point and I hope you're right.

 

[cheesepuffs]

What if the PYB is clearing the oil galleries and now things are the way they were supposed to be all along? If pressure is resistance than maybe sludge was causing resistance before causing my near-constant 30 psi when now my oil is flowing more freely and thus fluctuating with RPM more as it should be?

 

[OVERKILL]

Originally Posted By: cheesepuffs
What if the PYB is clearing the oil galleries and now things are the way they were supposed to be all along? If pressure is resistance than maybe sludge was causing resistance before causing my near-constant 30 psi when now my oil is flowing more freely and thus fluctuating with RPM more as it should be?


Sludge doesn't form in oil galleries and places of high flow, it forms in places where oil sits or runs across not under pressure. This is why it forms in the lifter valley, bottom of the pan, heads....etc.

 

[Zaedock]

PYB didn't clean much in a week. Just saying.


As far as Cumbie's gas goes, I use it all the time without issue.

 

[Fleetmon]

Any chance you may have excessive fuel dilution? That will clean the inside of an engine quick and will lower oil pressure due to decreased viscosity. That could, depending where its leaking, cause a rougher than normal idle, i.e. tbi leaking, etc.

 

[cheesepuffs]

Originally Posted By: Fleetmon
Any chance you may have excessive fuel dilution? That will clean the inside of an engine quick and will lower oil pressure due to decreased viscosity. That could, depending where its leaking, cause a rougher than normal idle, i.e. tbi leaking, etc.


I did just start idling my truck in the mornings this past week or so. Just because I want heat right away. But would it dilute that fast??

Also, regarding my filter, what if my ecore collapsed and there is a hole with a flap of ripped media that is opening and closing as I drive? When the hole is closed it would have normal resistance and maintain my normal 30 psi and then when that flap opens there would be less resistance thus my oil pressure reading would drop. And that would explain the quickly darkening oil if it isn't being filtered the whole time. Thoughts?

 

[OVERKILL]

Originally Posted By: cheesepuffs
Originally Posted By: Fleetmon
Any chance you may have excessive fuel dilution? That will clean the inside of an engine quick and will lower oil pressure due to decreased viscosity. That could, depending where its leaking, cause a rougher than normal idle, i.e. tbi leaking, etc.


I did just start idling my truck in the mornings this past week or so. Just because I want heat right away. But would it dilute that fast??

Also, regarding my filter, what if my ecore collapsed and there is a hole with a flap of ripped media that is opening and closing as I drive? When the hole is closed it would have normal resistance and maintain my normal 30 psi and then when that flap opens there would be less resistance thus my oil pressure reading would drop. And that would explain the quickly darkening oil if it isn't being filtered the whole time. Thoughts?


Nope. If there was a hole your engine would just be seeing unfiltered oil, it isn't going to have any sort of dramatic effect on oil pressure.

Regarding fuel dilution: Smell your oil, does it reek like gas? If an engine dilutes bad enough it can mask oil consumption/loss because there is fuel taking up the volume that used to be occupied by oil in the sump. The result is a sump full of a less viscous product that isn't able to lubricate as well as what it replaced.

 

[cheesepuffs]

Nope. If there was a hole your engine would just be seeing unfiltered oil, it isn't going to have any sort of dramatic effect on oil pressure.

Regarding fuel dilution: Smell your oil, does it reek like gas? If an engine dilutes bad enough it can mask oil consumption/loss because there is fuel taking up the volume that used to be occupied by oil in the sump. The result is a sump full of a less viscous product that isn't able to lubricate as well as what it replaced. [/quote]

No, the oil does not reek of gas. Even my old Valvoline had no presence of fuel odor. Just smelled like standard used motor oil.

Are you sure that a hole in the filter wouldn't effect oil pressure?

 

[OVERKILL]

Yes. Unless the filter completely collapsed inside itself and blocked the centre tube, or it has ingested some incredibly heavy sediment that has severely restricted the filter AND the in-block bypass, it should have no noticeable effect on oil pressure. A tear will just let oil through. Oil through, even when it is dirty, is flow.

Now another possibility is that something is blocking the oil pump pick-up, which has the potential to reduce observed oil pressure.

Are you able to verify the oil pressure with a mechanical gauge? Do you have access to a camera that you could use to take a look at the pick-up without pulling the pan?

 

[cheesepuffs]

Originally Posted By: OVERKILL
Yes. Unless the filter completely collapsed inside itself and blocked the centre tube, or it has ingested some incredibly heavy sediment that has severely restricted the filter AND the in-block bypass, it should have no noticeable effect on oil pressure. A tear will just let oil through. Oil through, even when it is dirty, is flow.

Now another possibility is that something is blocking the oil pump pick-up, which has the potential to reduce observed oil pressure.

Are you able to verify the oil pressure with a mechanical gauge? Do you have access to a camera that you could use to take a look at the pick-up without pulling the pan?


I'm not trying to be a pest here, just trying to get to the bottom of this. Doesn't higher/easier flow actually lower the psi reading? Meaning, if the oil was flowing through an open hole as opposed to the filter media, there would be less resistance and therefor a lower psi reading?

And no, I don't have a mechanical gauge or a camera unfortunately.

 

[OVERKILL]

Originally Posted By: cheesepuffs
Originally Posted By: OVERKILL
Yes. Unless the filter completely collapsed inside itself and blocked the centre tube, or it has ingested some incredibly heavy sediment that has severely restricted the filter AND the in-block bypass, it should have no noticeable effect on oil pressure. A tear will just let oil through. Oil through, even when it is dirty, is flow.

Now another possibility is that something is blocking the oil pump pick-up, which has the potential to reduce observed oil pressure.

Are you able to verify the oil pressure with a mechanical gauge? Do you have access to a camera that you could use to take a look at the pick-up without pulling the pan?


I'm not trying to be a pest here, just trying to get to the bottom of this. Doesn't higher/easier flow actually lower the psi reading? Meaning, if the oil was flowing through an open hole as opposed to the filter media, there would be less resistance and therefor a lower psi reading?

And no, I don't have a mechanical gauge or a camera unfortunately.

No, because the filter isn't the source of the oil pressure (pressure is resistance to flow), your ENGINE is the source of the resistance, which in turn, gives you your oil pressure.

You can reduce that pressure in a few ways:

1. Damage the pump. If the pump can't move the same volume of oil, pressure is going to be reduced.
2. Broken relief spring on the pump. Changes the observed pressure the pump needs to see to start bypassing oil back into the sump
3. A restriction in the system upstream of the pump, but downstream of the sender (if the filter imploded and blocked things)
4. A restriction in the inlet side of the pump reducing its ability to move an adequate volume of oil
5. Mechanical wear upstream of the sender that is resulting in the engine providing less resistance to oil flow. This can be through the form of worn bearings, a popped out oil gallery plug....etc.

 

[cheesepuffs]

Okay let's backtrack for a second. Before last night, my psi would always stay at 30-33. Even at idle, it was holding 30. Is that strange? For oil pressure to stay that constant regardless of idling or driving at different RPM?

 

[cheesepuffs]

I'm beginning to think that my oil pressure being reduced to half at idle is actually how it was supposed to be all along. That actually seems normal, no? Alarming to me because it's a change but it might not be bad afterall. ?

 

[OVERKILL]

It sounds like it was acting like a dummy gauge (maybe the sender was stuck?) before.

You can always verify with a new sender.

BTW, 16psi hot at idle is a bit low for an SBC.

 

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I'd verify with a mechanical gauge. Then I suspect the gauge itself or the oil pressure sending unit needs replacement.