How to tell if a filter is full?

[Patman]

I've heard that one way to tell if an oil filter is full and constantly going into bypass mode is to
feel the filter after a long drive, and if it's not hot, that means it's in bypass mode and is no
longer filtering. Is this true?

I emailed a tech rep from AC Delco Canada to find out how long the AC Delco PF35 filter that
I will be using will last before plugging up. I suspect that these filters can hold quite a bit of dirt,
and can easily go 15k or more before filling up. They would have to, I would think, since
GM now specifies 15k oil changes on the Vette, and that's with a super tiny PF44 filter,
which is considerably smaller than the PF35.

I'm definitely going back to extended oil change intervals this fall, and would rather not
change the filter during the duration if I don't have to. As the filter gets more dirt in it, it should
filter smaller particles too. So if it starts out filtering 98% of particles 25 microns and larger
(this is the AC Delco's rating) maybe after 5k it will start filtering 98% of particles 15 microns
or larger now?

As a side note, how long do you guys think a Mobil 1 filter (which filters out about 98% of 10 micron and
larger particles) would last before filling up? 5k?

 

[BOBISTHEOILGUY]

I've gone as long as 12,000 miles on my m1 filter before changing it and the oil. If my filter needs changing, Then I also change my oil.

 

[widman]

What you say about whether the filter is hot or not depends on the filter. If it is a Fram, or one of the others with the bypass valve built in to the retention valve in the base, that is TRUE. If it is one of the other filters - 80% of what I have cut open - the by-pass valve is on the far end of the filter, so oil still goes down the outer part of the filter, and if it hasn't been able to penetrate the paper element, it pushes thru the valve on the end, returning to the normal flow path with whatever oil has passed. The absolute best way woulld be to have two oil pressure guages, one before and one after the filter. But since that is not the normal setup, your best way to tell would be to know your oil pressure when the oil and filter are new. You will see it increase as the filter clogs.
But in reality, unless you are using the real bad ones, (I've cut "identical" filters that varied from 900 to 3600 sq.cm.) they can hold about as much as you want with a decent oil. I have test results of 3 CH-4 oils when they first came out. At 200 hours they all passed the API test of 11.45psi increase by a wide margin. But if extended to 400 hours, one increased by 79 psi, another by 19 psi, and the third by 10 psi.
Also, your Group I oils will hold a lot less soot than a Group II, III, or IV. Their graphs start separating immediately, and by 3% soot there is almost an 8 point difference in rotational viscosity. By 5% soot the group II, III, and IV have increased by 8 points, but the Group I's have increased by 50 to 60 depending on their Soluble and aromatic content.
Also depends on the original viscosity. I've seen people put SAE 40 in and start the engine at 50 degrees F, pegging the oil pressure needle. Obviously passing directly through the by-pass valve.

 

[Al]

One point-this is true (cold filter) on GM cars bc they have an internal bypass valve in the engine (none in the filter). I assume many Non-GM cars don't have internal bypass valve-but don't really know.

One question. An individual on another board indicated that he always sees metal marticles on filters he and his friends cut apart. When I told him I have never seen metal particles in any of my filters-he acted as though I came from another planet. Any experience in this area?? I'm thinking the guy and his friends just beat the crap out of their cars

(He is a younger person)

 

[VaderSS]

How is he cutting them apart?

 

[user151]

"your best way to tell would be to know your oil pressure when the oil and filter are new. You will see it increase as the filter clogs."

I thought the usual oil pressure reading was after the filter... and as the filter clogs, the pressure BEFORE the filter would increase, but that is not what is shown on the gage.

If I am right I would have to disagree, but feel free to correct me....

 

[Gary Allan]

In most cases, any restriction will increase pressure. If you're reading the pump side of the filter (as opposed to the engine side) ..you would still see a decreasing pressure as the visc decreased, but it should settle at a higher level.

That would be one loaded filter ..or one accurate gauge, imo.

 

[SuperBusa]

Originally Posted By: user151
"your best way to tell would be to know your oil pressure when the oil and filter are new. You will see it increase as the filter clogs."

I thought the usual oil pressure reading was after the filter... and as the filter clogs, the pressure BEFORE the filter would increase, but that is not what is shown on the gage.

If I am right I would have to disagree, but feel free to correct me....


Yeah, you are right.

If the oil pump is not in relief mode, then you won't be able to tell if a filter is becoming loaded or not if you are reading only the engine oil pressure (ie, pressure gauge located after the filter).

This is because when the pump in not in relief mode, 100% of it's output volume is going through the filter/engine circuit. As the filter loads up, it just takes a little more supply pressure to achieve the same pump positive displacement flow rate, so the PSID will increase across the filter but the engine oil pressure will remain the same because the same positive displacement flow volume is still going through the engine. Under constant viscosity and RPM conditions, the engine's oil pressure is basically an indication of how much flow rate is going through it.

If you had a pressure gauge before and after the filter, you would see the pressure increase above the filter as it loaded up and the engine pressure remain the same until the pump went into relief mode. In pump relief mode, the pressure is (ideally) held constant and the flow will be dependant on the filter/engine flow resistance. If the filter becomes loaded (ie, more flow resistance), then you will see the engine oil pressure drop under these conditions.

So, the bottom line is that you will not see if the filter is loaded (or just plain restrictive) unless the oil pump is in relief mode (ie, cold oil with some significant engine RPM) if you are just looking at the engine oil pressure sensor located after the filter. You would have to compare the cold running conditions/pressure with a used filter to a new same p/n filter to see the true delta due to difference in restriction. Once the pump is out of relief mode, the filter's PSID becomes transparent to a pressure sensor located after the filter. You would need a pressure sensor before the filter to see it's relative restrictiveness when the oil pump was out of relief mode.