Five sided w123 300D oil filter!!! Why??? - PeachParts Mercedes-Benz Forum

unkl300d · #1 05-10-2002, 01:20 AM

After changing the oil on my '79 300D, I observed the
old Hengst oil filter had undergone a transformation of shape!!

Normally the filter is cylindrical in shape.

This one's top half, the screen mesh half, had five flat sides.

Apparently the filter had undergone some type of extreme
vacuum like force which pulled in the sides to almost flat
sides. Five sides. (pentahedron?)

Any ideas on how this happened?
approx. 3500 miles on the filter.

Thanks!!

unkl300d · #2 05-10-2002, 02:06 AM

Well, I was not aware of that, but I replaced it with a Mann filter.

I have one other Hengst on the shelf.

I am curious also.

X Files???

can-do · #3 05-10-2002, 02:17 AM

Greetings UNK,

I just posted that same topic not more than a few days ago about the very same filter and I had the same results with it when I changed it out. I had one Mann on hand and used it as my replacement but I also have to more of the collapable types as well and had an order in for two more that arrived the other day. Hope there isn't a defect in the filter design otherwise several of us that buy four to six at a time are out some cash. I intend to pull the filter cover in the next couple of days and see what the Mann looks like after about 500 miles. Someone had mentioned the check valve in the stem perhaps sticking, but I can hold a lot of credability to that just yet as I'd think oil would be a sufficient lubrication to deter the check valve from sticking. Will try to keep you posted.

Charles

JimSmith · #4 05-10-2002, 10:03 AM

unkl300d and can-do,

After reading this and kind of having a hard time understanding how the problem could be associated with the filter brand, I got the manual out and studied the flow paths into and out of the filter and filter housing.

The only thing that can cause the deformation you describe is a pressure differential across the thin perforated metal "can" on the outside of the very fine filtering segment (upper 2/3 or more) of the filter where the outside pressure is substantially higher than the inside pressure. Since the can is perforated, there can be no static pressure differential across this can. So the only way to get a significant differential pressure is with a low flow resistance on the part of the flow path on the inside of the can. Flow in this path is controlled by a solid sheet metal disc at the bottom of the fine filter volume, separating it from the bulk filter volume below it, the seals on the center tube, dubbed the return flow tube in the manual figure, the small orifice admitting flow to the center return flow tube channel, and a check valve inside the tube about 25% of the way up from the very bottom of the tube.

There is a similar inner can shown in the manual figure, along the inside diameter of the filter. Maybe one of you guys can look to see if this is also deformed.

The check valve allows flow down the center return flow tube, where the flow is returned to the oil sump and apparently not in the other direction. While it may be possible for this check valve to be defective, I doubt it can just fall out, and if it is stuck open, the flow in the normal direction will not be increased enough to cause the pressure difference necessary to deform the filter's outer can (and possibly inner can). This is because the flow path with the valve hung up in the open position is nearly identical to the flow path with the valve operating normally and the flow losses will be about the same for this path as they are controlled not by the check valve but by the little orifice in the side of the flow return tube. Additionally, the check valve cannot determine the brand of filter, so if Hengst filters are doing this and Mann ones are not, the check valve cannot be the issue.

The other two flow path controls are very likely the source of the problem. The upper filter section is intended to provide a flow rate that is lower than the bottom portion, as it is essentially a bypass filter built into the same housing as the main filter. So, the discharge side of the main filter, a relatively low flow resistance path, is isolated from the relatively high resistance path of the bypass filter discharge. This high resistance path is what limits flow so the bypass filter structure can be inexpensive and light so it does not crush - otherwise it would have to be made of substantially more robust materials, including the filter element inside the can (usually a low resistance path, especially when new, but with next to no structural integrity to withstand high differential pressure) or a separate item altogether.

So, there is a rubber grommet like seal on the top and bottom of the bypass section that seals against the center return flow tube, preventing dirty oil from going around the whole filter at the top, and keeping the very finely filtered oil that passed through the top section on its intended path to the little orifice on the center return flow tube and down through the check valve to the sump. If this lower grommet seal is either not there or sized wrong, or coming off at installation for some reason, the bypass filter flow will join the main flow down a low resistance path. A new Hengst bypass filter element, nice and clean with lots of surface area, will try to pass lots of oil flow. That flow will create a differential pressure that likely could deform the outer, and possibly inner, cans.

If the bottom sheetmetal separator between the bypass and main filter segments is damaged, or missing, the bypass filter discharge will also access the low flow resistance path and cause the same effect, except the inner can will likely not be damaged.

So, I think one of the bent filters should be visually examined and possibly cut in half to see what the problem is. If more than one of these is like this, there is a manufacturing problem that Hengst should be willing to fix for free. Otherwise we should all avoid these filters. I doubt the condition damaged anyone's engine, but it is not what the Mercedes-Benz engineers designed, so it is not something that should be tolerated.

If the grommet is coming off when you put the filter housing cap, with the return flow tube attached, on with the filter in the housing, maybe this part needs to be lubricated with engine oil as part of the procedure. This should be apparent by feel, comparing a Mann installation to a Hengst one, the Mann assembly should be less effort. I usually lube the o-rings at the bottom and top, but do not go out of my way to slather the return tube with oil at assembly. I have never seen this deformed can situation either.

I hope this helps, and good luck. I will avoid Hengst filters for the time being. Jim

unkl300d · #5 05-10-2002, 11:59 AM

I will attempt to take pictures and then dissect.

I've never posted pics here before , so it may take a week.

Thanks Jim and Can Do.

I think I'll check my new Mann filter as well after a month.

Denis

leathermang · #6 05-10-2002, 12:09 PM

GEE , JIM, I was going to go for " your car has five cylinders so obviously it would get sucked into a pentagon ".....

Greg

JimSmith · #7 05-10-2002, 12:48 PM

Greg,

Hmmmm, I hadn't thought about why it is five sided (pentagon?). Adding that to the problem to be solved makes the five cylinder theory sound pretty good, I mean, none of us can ponder these issues endlessly and five sides with five cylinders - does anyone really think that is merely coincidental? (LOL)

Lets see if the inner cans are five sided, and if so, that should be proof enough, right?

Sometimes you just have to take things at face value. Jim

leathermang · #8 05-10-2002, 02:14 PM

I have a friend that knows that 'contrails' behind jet planes are composed of chemicals the government is spraying on us...Given his other theories I am more inclined to believe that the chemicals are landing on him, but that may also explain these filters compressing into themselves imitating black holes....and it is black in there when they do this if it is diesel oil they are swimming in...Are any of our Chemist forum members involved in mixing these chemicals the government is spraying on us ? I know, Iknow,,you could tell us but then you would have to kill us.....

Greg

#9 05-10-2002, 02:59 PM

I've just (in the last 2 weeks) changed out two Hengst filters--no problems of deformation.

Changing filters, you're supposed to blow compressed air through the center tube, to make sure it isn't plugged. I suspect most people don't do this. The first time I did, it took me a half hour to clean the tube out.

Jim's analysis could well be right (too complicated for me), but the first thing I'd do is make sure the center tube is clear.

jcd · #10 05-10-2002, 03:02 PM

Your buddy's theory sounds about as plausible as the "Russian Crude Oil" based diesel is causing the idle surging problem.

BTW, although I did have the mysterious idle surging symptom this winter, it has gone away. Maybe the Russian Crude left the market.

JCD

JimSmith · #11 05-10-2002, 06:18 PM

dweller and unkl300d,

I am sure the little spring loaded check valve in the return flow tube is important to proper functioning of the filter. For example, if the valve fails to open the whole top two thirds of the filter becomes inert, as no oil can flow through it. All the oil has to pass through the bottom, less restrictive part, which means the oil does not get cleaned as intended. That will eventually lead to accelerated wear of the engine's bearings and other critical parts.

However, if the check valve is plugged there is no mechanism to generate a force to collapse the upper can. Remember, it is perforated to allow oil to pass into the filtering media, so if there is no flow, the pressure on both sides of the can will be equal and there is no reason for it to deform. Also, the restriction of the orifice in the side of the return flow tube would normally make the pressure drop across the filter element very low, exposing the grommet seal to nearly the maximum oil pressure most of the time. So it is unlikely the plugged line will cause the grommet to fail either, but I guess it is possible. This would still not explain the Mann filter being immune to the issue.

I did not try to be confusing in my explanation, but apparently was. Please excuse me if I got too long winded and hard to follow.

By the way, I have never tracked the manufacturer of oil filters I have changed over the last two decades, and have never seen this problem myself. Without any data that adds another brand, I think it is likely an issue with a batch of these things from this vendor. I will stop here as I do not want to monopolize the forum on this topic. Good luck and I am waiting for those photos! Jim

can-do · #12 05-11-2002, 02:51 AM

Greetings Jim,

I wished I had saved the filter, but it's part of our future oil reserves in the making now. I did look on the interior of the filter before discarding it and the interior metal was not deformed in the least. Whatever the pressure was that was applied, it was most likely a vacuum from the interior of the filter assembly. Looking at the oil flow diagraphm in the manual, I still find it hard to believe that the pressure or vacuum could be that great to collapse a filter like that unless oil suction pressure became so great and the bypass valve didn't open forcing oil to be pulled from the top filter only and sheer volume of oil created the collapse. Hey, I'm open to ideas as I still have four Hengst filters to use up. I think I'll pull the lid off the filter assembly when I get a day I'm not at work and blow the center tube clean with air to see if that has an impact on operation.

Charles

The Warden · #13 05-11-2002, 03:44 AM

Just my opinion, but, to me, it sounds a lot like Hengst got a bad batch of filters made. Maybe one of the workers got mad and did substandard work.

IMHO it'd be best to see if this is happening with other filters...

JimSmith · #14 05-11-2002, 02:27 PM

Going to try once more to make the point. There has to be a mechanism to develop the force necessary to crush the outer can on the bypass section of the oil filter.

This force can not be generated by static conditions as under static conditions (no flow) the pressure on the outside and inside of the can are equal. This is because the can has holes in it (90 of them on a MANN filter as I just counted them on one I have on my desk waiting for the 240D to come back from Troy, NY for a service) which cannot sustain a static differential pressure (the pressure will equalize through the holes). Since all the flow through the upper portion of the filter goes in the little hole in the return flow tube at the center of the oil filter housing cover, and down to the check valve, a blocked check valve will generate a static flow condition and no chance for deforming the outer can on the bypass filter section.

Consequently, the force must be generated by some other conditions. At very low flow rates the situation is much like a static pressure situation. As the flow through the 90 holes is increased by lowering the pressure on the downstream side, the resistance to this flow increases (like drag on your car - at 5 mph it is hard to measure the air resistance but at 80 mph most of your engine's output is devoted to overcoming air resistance to the car's movement). This increasing resistance can sustain a differential pressure across the perforated surface of the can.

Under normal flow conditions the flow rate in the upper, bypass section of the filter is kept low by the size of the hole all the flow must travel through in the side of the return flow tube, and the resistance of the check valve mechanism. At the normal conditions there is very little resistance at the 90 holes in the outer can, as they have about 90 times the flow area of the single hole in the return flow tube.

So, to make conditions that will develop the necessary forces, there needs to be substantially higher flow through the upper, bypass portion of the filter and its outer can. A plugged return flow tube check valve will not generate this condition unless the pressure across the rubber grommet seal at the bottom of the bypass filter section (about one third of the way in the filter looking from the bottom) that results is enough to pop the grommet off. I doubt this can happen, but it is a possiblility. The grommet seal failure would allow the bypass filter flow to access the low resistance flow path of the main filter element.

So, a scenario where high flow in the upper section of the filter is needed, and any one that happens is good enough for me. I think the inner can is much less likely to deform than the outer can, just by the fact that it is much smaller in diameter (less surface area). Suggesting it might have been deformed could have been a red herring and added to the confusion.

I hope this helps, Jim

leathermang · #15 05-11-2002, 04:19 PM

GEE, JIM, you remember the story of the poor cobler and his wife where Gnomes came into the shop at night and made the shoes for him ? That was going to be MY next theory.... Gnomes hammer these things into pentagons as part of a satanic ritual....

Only on nights immediately following being sprayed by 'Contrails' of course..... Greg