I'll start with the story then ask the question. I have an 07 a4 Avant with the 2.0T. Normally I have the car serviced at the only place I trust down state (Michigan). Long story short I changed the oil and used a NAPA Gold filter instead of waiting. 4000 miles into that oil change my oil pressure light comes on (spring time, car warmed up and cruise set). By the time I could get off on the shoulder it was too late (the motor was knocking). I called my shop and he already new what the problem was, sure enough I had it towed there. They checked and the oil filter cartridge looked like a crushed beer can.

They said they see a lot of that in the "cheaper filters". Has anyone here heard of this potential problem? The findings by NAPA/WIX said it was a problem with the car and not the filter. I guess at a minimum at least it's a heads up. With the price of a new long block I will never make that mistake again.

Any knowledge in this area would be appreciated.

 

I have only seen that once before. A better mechanic then me told me that when the oil pump ran out of oil it started to suck air causing the filter to collaspe some. I think that might be what happened here as well.

 

I suppose it's possible, but with cruise set on a flat highway and oil level at the full mark I'm just looking to check out all the possibilities. After paying a little over $9000 for a new long block to be installed I just want to try and remove any possible external weak areas.... Love the car too much.

 

A couple points, this is mostly to address some other misinformation that I've seen on the internet.

Oil is pushed through the filter, not sucked

I've never seen a car with the filter "pre" oil pump. The pump "sucks" oil from the crankcase through the pickup/strainer. That's the only "filtration" it gets. Too much filtering on the suction line can lead to cavitation and a number of other problems, so suction line filtering is usually limited to mesh strainers or more porous filters than conventional oil filters.

Oil pumps create very little air pressure/suction

The gaps in oil pumps can be measured with feeler gauges and they are not "air tight". Gear pumps work by forcing a fixed amount of oil from the low pressure side into the high pressure side. Once there, it's easier for the oil to move forward than creep back through the imperfect seal.

Oil pumps are considered self-priming to a point, meaning they can create some "suction" to get oil flowing, but if no oil flows they won't create much more suction (and corresponding pressure). It's kind of like a rotary engine without apex seals, which basically have no compression - meaning the pump isn't really suited to making much pressure to begin with. To make matters worse air pressure is going back to the very place where the pump is trying to create suction - the sump. It's like a dog chasing it's own tail.

To overcome this dry sump (racing engine) oil pumps usually use 4+ "stages" of pumps. In other words four or more pumps in the row and housed together with some oil splashing through to keep things sealed are necessary to create the roughly "equivalent" of 4-6 PSI of vacuum (i.e. 8-10 inches HG (mercury)). They also have breathers to eliminate the dog-chasing-tail phenomenon.

In ordinary cars actual crankcase pressure is determined by PCV design and function. In a simple naturally aspirated engine, stuck open you have too much vacuum and stuck closed you have positive pressure from blow-by. Properly functioning, the crankcase is at a very slight vacuum, usually a few inches of water, "equivalent" to 1 PSI. I won't run the test, but I'd be surprised if that changed if you run an engine without oil and gave the oil pump a chance to pump some air (before the car eventually dies of course, which takes a surprisingly long time...).

The correct oil pressure is not regulated by the filter bypass valve

Fluids, for practical purposes, are virtually incompressible. This causes a problem, because the amount of oil that flows per revolution is fixed, while the number of revolutions varies. Yet oil can't compress to 'average' these differences. To have enough oil under idle, you necessarily have too much at high speeds.

To overcome this cars have oil pressure relief valves that are completely separate from the oil bypass valve found in the oil filter. For my old Subaru, for example, the pressure valve in the pump would open at ~ 73 PSI, resulting in the excess oil being directed back into the pan, in effect exiting the "pressurized" portion of the lubrication system. I mention the Subaru because it was not uncommon for them to experience stuck relief valves or have the return passage blocked with sealant upon reassembly in "built" engines. I also remember the Subaru values and can't be bothered to look them up for the B7 . The numbers would be similar and the concepts identical.(***As an aside, very new cars are beginning to deploy variable oil pumps to overcome this recirculating inefficiency - they work like variable vane turbos - but our Audi's do not have these. Also, vehicles can have multiple pressure valves too...)

The bypass valve in the Subaru oil filter would open once the pressure from the pump (pre-filter) was 23 PSI above the pressure after the filter. That is a relative measure. Meaning if the pressure regulating valve is designed to open at 73, then the filter bypass valve doesn't open to overcome excess pre-filter pressure, but rather to correct or overcome inadequate post-filter pressure caused by the filter itself. When the bypass opens, oil does not exit the pressurized system but merely bypasses the filter and moves on to the next stage unflitered. (This isn't a big deal and filters are not 100% efficient for smaller stuff anyway - the design relies on "getting it next time".)

So if the car is creating the full 73 PSI of pressure, the post-filter pressure would need to drop below 50 PSI for the filter bypass valve to do anything. If the pressure regulating valve stuck shut and the oil pressure spiked to 150 PSI, so long as the filter could handle the resulting flow of oil, the bypass valve, again, wouldn't do anything. In other words, pressure pre and post filter would be equal (less any drop from the resistance of filtering...). But what if the filter couldn't handle the flow? Once the resistance creates a pressure difference equal to the bypass setting, the valve will open up. While in bypass, it's as if the filter wasn't there.

In other words, the engine is designed to work as though the filter wasn't there. This, of course, is because unfiltered oil is far better than no oil. Just think about all the four stroke engines that use splash lubrication and no oil filter. They usually specify 50 hour intervals, which is equivalent to a few thousand highway miles. The horror!

Running an engine without a filter will not cause imminent engine failure.

You'lll find countless stories of people doing 5K+ on their cars after garages forget to install canister style oil filters. Hundreds if not thousands, not to mention all those that were never "discovered" by the customer. I've never heard of any engine failing as a result. Bob Winters (the "Bob" of bobistheoilguy) ran his Ford Escort on several OCIs without ANY filter: DIFFERENT OILS AND NO FILTER ON ENGINE | Used Oil Analysis - Gasoline | Bob Is The Oil Guy .

Now I don't want to get into the validity of the test, etc. but the point is that the chances of killing your engine by driving without a filter for a few thousands miles are remote if everything else is in order. Drive through the desert without an air filter AND oil filter, sure, you'll run into problems. But think about all the people with crappy Fram filters that tear if you sneeze on them. The oil filter will kill an engine if it blocks the oil (i.e. self destructs and clogs bypass valve, oil pressure builds but the pressure relieve valve just dumps it all back into the pan). But the canister filter design makes that more difficult have have happen, and doesn't appear to have happened here.

I've already gone on WAY too long here, but one last thing. If you tear down an engine you'll see all the crap the bearings collect. One of several bearing properties is called "embeddability", or the ability to embed contaminant in the bearing material. It is eventually pushed below the bearing surface to prevent scarring. Basically part of the bearing takes one for the team. My point is that between detergents in the oil for the really small stuff, gravity for the heavy stuff, the oil strainer for the big stuff and bearing emdeddability for the in betweens, your engine should not have failed.

How did your engine fail?


Hopefully your mechanic can provide a better answer than blaming the filter.
What is the actual hypothesis for how it caused the engine to fail? Did they drop the pan and open the top before replacing the engine? What if the chain driving the oil pump and balance assembly failed? You said the engine was knocking. Do you mean like ignition knocking? Rod knocking? Engines that fail usually have oil filters jammed full of metal shards. If unfiltered oil killed your engine, the aftermath would be all over that filter. It's not.

Did you start the engine again afterwords? The intake cam timing is adjusted with oil pressure. When you turn off the vehicle it locks into the position needed for starting. Once you start it up it's supposed to pop out of that above 10 PSI ish of oil pressure. If you've got an oil pressure problem, you sometimes see those errors pop up first.

I'm sure there were plenty of stored codes along with whatever was going on. If I was you I would have wanted to get a good look inside that engine!

If you want to see what happens when the oil pump fails (not all results are the same...) look at this thread: https://www.audiforums.com/forum/b7-...-143922/page9/

Cheers and best of luck with your new engine!

 

Honestly, WIX filters are among the best out there. With that said, I can say Napa filters are the best too, because wix makes them for napa. My belief is that the filter was not at fault, something else caused it to crush. Hopefully you won't have that problem again though.

 

No doubt Wix makes a good filter. Just like Snap-on makes a great wrench. But just because it's Snap-on doesn't mean you can use your 3/8" on 9mm bleeder without making a mess of it.

In my mind if the OEM filter is good and cheap, use it. The Mann filter (OEM) is under $10. Why experiment? On my Kubota Wix filters were more money than OEM! And the Kubota filters are some of the best I've seen (whoever makes them...).

This is especially true with canister filters, because the filter has to work perfectly with the existing design. At least a screw-on filter is self contained and as long as it threads on and seals it should work as designed. Whether or not it is designed exactly to factory specs is less of an issue, as long as it IS working.

I remember some Ford powerstrokes had issues because certain aftermarket canister filters came with their own screw on cap that was a different size. I believe they were actually Napa (i.e. Wix!). If you put an OEM filter on with the non-oem cap, it wouldn't actually secure the filter - just like having no oil filter! Much easier to get the right part to begin with.

All that said, the 'right' part won't always be the best part. I use Mobil 1 filters on my diesel Jeep because the OEM filter was way overpriced and poorly constructed. I buy three or four when they go on sale. I used to use Quaker State (made by Purolator) on my Subaru after the OEM filter changed to the crappy blue ones. Either way, I'll always need a reason to buy non-oem, beyond saving 5 minutes or $3.

If in doubt, I'd rather leave the right filter in for two OCI's than use the wrong filter. Many industrial engines call for changing the engine oil before the filter. I think Honda did this for a while as well. Most good filters work better after a few thousand miles than new (both air and oil). If you don't have the right part, leave it be!

True story - my B7 had the engine replaced for free outside of warranty. Without going into details, it helped a lot that the dealer had done every oil change on the car since new (1 owner, same dealer). This wasn't completely intentional but it worked out that way. When the engine failed, it had an OEM filter and oil they had installed a couple months earlier. Would they have denied the claim if I'd used Wix/Mobil 1/Etc.? Possibly. I work on all my cars extensively, but dealer oil changes were very cheap insurance in this case.

I guess the point is that using OEM parts/dealer services just eliminates the finger pointing. The OP wouldn't have made this post if the engine failed with an OEM filter, even if the underlying cause was the same. In my experience they'll often look for the first plausible excuse for why something failed. As an owner my goal is to eliminate any reasonable excuses possible without being robbed by the dealer.

Happy motoring, whichever filters you choose!

 

I agree with what you said above, use OEM when you can because the car was engineered for that filter to be used on it, but if you or they choose to use a different filter, there are crappy ones out there and there are good ones too. As picky as Audis are, I use nothing but OEM stuff. On my truck, I'll use wix. But to each their own!