I did some checking on this recently and found the oil pressure sensor/sender is getting its pressure reading from the clean, filtered oil side of the oil filter, between the filter and the oil galleries on the 4.0 engines. Under normal conditions as the filter gets plugged up the oil pressure, or GAUGE pressure will drop, until or unless the bypass valve on the filter opens allowing unfiltered oil to bypass the filter and go directly to the engine, or if the filter is defective or damaged, and it goes into a bypass mode due to the damage.
On a 4.0 engine the oil filter will not normally add pressure to the gauge pressure at any time, as it is on the wrong side of the plumbing.
I disagree with geeaea's claim that there is little or no pressure drop across the oil filter media. I do not have actual test data, but all my industrial filter experience tells me there is some pressure drop across the oil filter, even across a new oil filter, maybe as much as 5 psi. I have never seen a filter that did not create a measurable signiificant pressure drop in service.
As geeaea has pointed out with the blip at start up comment, there maybe a larger pressure drop across the filter as the oil galleries fill up, but once the flow is restricted by the engine itself there will be less flow through the filter, and thus less pressure drop across the filter.
So why would there be a substantial pressure drop (differential) across the filter when the oil pump is in the relief mode only? That happens at 75 PSI as you pointed out, so why would this happen (large diferential) at 75 psi and not at 60 psi (large differential)?
OH, and I found this comment real interesting!
geeaea said:
Most nitrile ADBV will decay/degrade within 3k ...maybe sooner. That's a Fram signature characteristic.
I knew that silicone ADBVs are better, far supperior to nitrile, but I did not know the nitrile in the Frams would fail that fast. I knew the Fram ADB valves were no good, sometimes don't even work right out of the box
, but that is most interesting to hear that nitrile seal material they use can fail that fast.
geeaea said:
I beg your pardon? In an otherwise functional engine with a viable oil pump, just how does a filter effect anything? A filter MAY add pressure elevations between it and the pump to a very minor degree ..virtually nothing. You may get a blip at startup ..but once the galleries are full ..the filter is as though it isn't even there. The only time that there is substantial differential across the filter is if the pump is in relief. I guess if you left it on too long, you may actually be able to load it enough to produce some measurable PSID.
Mikeforte said:
I'm with him unless you have a real high milage or this is a new development. If either is the case then the oil filter is your only answer to such a problem IMHO.
