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1950Dodge

By-Pass Oil Filters: How Effective?

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I’m tired of reading on internet blogs and forums about how “ineffective” a by-pass filter system is on our old cars. I’ve even seen posts and comments from supposed knowledgeable mechanics that advise against adding back the by-pass circuit when doing rebuilds of engines that have them.<o:p></o:p>

I’ve got one of these systems on my 1950 Dodge Coronet, and all this “ineffective filter” commentary was counter-intuitive. Why did manufacturers add them? Cadillac, known for its superior engineering, used a by-pass filter on its new 1949 OV design, and did not change to full-flow filtration until 1962. Nevertheless, I wondered, “Is the filter on my car just an “appendage” that was added for marketing purposes, or does it really help to keep my oil cleaner?” After doing some research, I’ve come to the conclusion that not only is the by-pass system NOT ineffective, it actually is pretty effective, even if not as “good” as the full-flow systems that are standard issue today. Here is some good information on this Forum, from people who appear to be knowledgeable:<o:p></o:p>

http://forum.studebakerdriversclub.com/showthread.php?46568-62-64-Studebaker-V8-full-flow-blocks-versus-51-62-by-pass-filter-blocks-a-discussion<o:p></o:p>

An engineering friend came up with what I think is a good, non-technical common sense way to explain the effectiveness of by-pass filtering. He says to think of swimming pool filtration. That is essentially a by-pass situation, where a small portion of the pool water is drawn into the filter and then returned to the main (dirty) body of water. I’ve observed many times absolutely filthy black pool water, after having sat all winter, become crystal-clear and sparkling after 2 or3 days of by-pass filtering. I’d say that’s pretty effective filtration.<o:p></o:p>

So, IMHO, if your oil supply starts out clean and you have a by-pass filter, you will come out OK in the clean engine dept. The only time a by-pass filter may not be effective is if the oil becomes suddenly contaminated, such as if you were driving in a severe dust storm with an open-crankcase ventilation system. A full flow would get 99% of the immediate contamination on a single pass whereas a by-pass might take 30-45 minutes to remove it. A lot of damage could result in that time. But, under normal circumstances where we drive on paved roads, the chance of the immediate contamination is remote. <o:p></o:p>

I’ll stick with my by-pass filter, and I will continue to advise people who have no filters on their classic cars to add the by-pass circuit. Very easy to do, as opposed to trying to plumb a full-flow into a block not originally designed for it.<o:p></o:p>

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A bypass filter is MORE effective than a full flow filter, because it removes smaller particles of dirt. It also filters ALL the oil, contrary to rumor, it just doesn't filter it all at once.

It takes 10 or 15 minutes for all the oil to go through a bypass filter, in other words, all the oil gets filtered every 10 or 15 minutes.

The one drawback is, that it is theoretically possible for a speck of dirt to go round and round, through the bearings, and never happen to pass through the filter. This is the reason the full flow filter was invented. If you have hydraulic valve lifts, one spec of dirt in the wrong place can bung up a lifter. Old cars that never had their oil changed, often have clacky lifters not because they are worn out but because they are dirty and sludged up.

This is why they developed the full flow filter, not in the early days of cars, but 50 years later - after using bypass filters for years - right after they started using hydraulic lifters in everything.

The ideal would be to have a full flow for safety and a bypass for complete filtration. I saw a thread on the net about Frantz bypass filters that use toilet paper as a filter medium. The oil travels lengthways through the roll for depth filtration. One owner who drives a Dodge diesel Cummins engine truck, has his oil analysed every 5000 miles but NEVER changes it. The company that analyses the oil, advised him to stop wasting his money on analysis because the oil is always the same. They suggested he change the oil at 50,000 mile intervals. Every 1000 miles he changes the (paper roll) filter and tops up the oil, that's it.

ANY filter must be better than no filter at all, even if you don't like bypass filters, might as well keep it because it is doing something. If there is any difference in engine life between a bypass and full flow filter, given regular oil and filter changes, I think it would be very minor or none at all.

Edited by Rusty_OToole (see edit history)

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I’m tired of reading on internet blogs and forums about how “ineffective” a by-pass filter system is on our old cars. I’ve even seen posts and comments from supposed knowledgeable mechanics that advise against adding back the by-pass circuit when doing rebuilds of engines that have them.<o:p></o

I’ve got one of these systems on my 1950 Dodge Coronet, and all this “ineffective filter” commentary was counter-intuitive. Why did manufacturers add them? Cadillac, known for its superior engineering, used a by-pass filter on its new 1949 OV design, and did not change to full-flow filtration until 1962. Nevertheless, I wondered, “Is the filter on my car just an “appendage” that was added for marketing purposes, or does it really help to keep my oil cleaner?” After doing some research, I’ve come to the conclusion that not only is the by-pass system NOT ineffective, it actually is pretty effective, even if not as “good” as the full-flow systems that are standard issue today. Here is some good information on this Forum, from people who appear to be knowledgeable:<o:p></o

http://forum.studebakerdriversclub.com/showthread.php?46568-62-64-Studebaker-V8-full-flow-blocks-versus-51-62-by-pass-filter-blocks-a-discussion<o:p>

An engineering friend came up with what I think is a good, non-technical common sense way to explain the effectiveness of by-pass filtering. He says to think of swimming pool filtration. That is essentially a by-pass situation, where a small portion of the pool water is drawn into the filter and then returned to the main (dirty) body of water. I’ve observed many times absolutely filthy black pool water, after having sat all winter, become crystal-clear and sparkling after 2 or3 days of by-pass filtering. I’d say that’s pretty effective filtration.<o:p></o

So, IMHO, if your oil supply starts out clean and you have a by-pass filter, you will come out OK in the clean engine dept. The only time a by-pass filter may not be effective is if the oil becomes suddenly contaminated, such as if you were driving in a severe dust storm with an open-crankcase ventilation system. A full flow would get 99% of the immediate contamination on a single pass whereas a by-pass might take 30-45 minutes to remove it. A lot of damage could result in that time. But, under normal circumstances where we drive on paved roads, the chance of the immediate contamination is remote. <o:p></o

I’ll stick with my by-pass filter, and I will continue to advise people who have no filters on their classic cars to add the by-pass circuit. Very easy to do, as opposed to trying to plumb a full-flow into a block not originally designed for it.<o:p></o

Cadillac used a by-pass oil filter in 1957 on standard Cadillac, while 57 Eldorado gets the can type full flow type...the kind Pontiac used from 1955-1960. see the link of a 57 Eldo full flow 365 engine;

http://lh3.ggpht.com/_SuHaRG4eFas/SPZrVqRCCZI/AAAAAAAAAQs/ij-vHHAU-kI/s640/DSCN8453.JPG

I believe all GM went to the spin on full flow type in 1961 and I know for a fact Pontiac did.

FYI the can type shown in the picture in the link is the best type of filter, certainly the less messy because the can has a drain plug to first drain the oil and the filters in them have a much larger area than the short stubby spin on type.</o

Edited by helfen (see edit history)

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Cadillac had them as early as 1931, and probably a few years prior to that. They were sealed canister types. The owner's and service manuals show them and describe replacement intervals. Mine has been changed to a replaceable canister type. Although not correct, it is much cheaper. I see original NOS sealed Purolater units for sale on ebay from time to time for around $150. There is also a setup that hides a new type filter in an original looking can.

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Question: did Fram and Purolator use reinforced "rubber" flex hose to the filter canister? OR, is it correct to use a steal or copper line . My car has the Fram filter assembly mounted on the engine not firewall. I always thought that the flex rubber lines will fail with catastrophic results and these lines should be ridged, for durability. But, I see units sold new and NOS use flex lines. Which is correct?

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metal seems to be correct up to the fifties or sixties. I have seen remote filters on fork lifts that came from the factory with rubber. They were built in the eighties.

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Question: did Fram and Purolator use reinforced "rubber" flex hose to the filter canister? OR, is it correct to use a steal or copper line . My car has the Fram filter assembly mounted on the engine not firewall. I always thought that the flex rubber lines will fail with catastrophic results and these lines should be ridged, for durability. But, I see units sold new and NOS use flex lines. Which is correct?

Pontiac, because of it's unique oiling system on straight eight (1933-1954 and derivative flathead six (1935-1954 never had a bypass oil filter, but dealer installed units were available. The ones I have seen on those Pontiac's had reinforced rubber hose...see the link;

http://assets.hemmings.com/story_image/482431-500-0.jpg?rev=2

Porsche used a bypass system on the 356 series and 912 series and used a braided metal over rubber hose lines. Okrasa, which made high performance VW kits used the same type of bypass filter and the same type of oil line as Porsche. See the links;

Porsche engine; http://images.thesamba.com/vw/gallery/pix/894866.jpg

VW Okrasa;http://photos.imageevent.com/mrokrasa/porscheenginebuilds/mike195436hpokrasa/websize/Okrasa%20Mike%20Chapman%204.jpg

None of these systems were ridged even though they were fixed to the engines. If you had a filter on the firewall I would think you would really want a flexible line for sure!

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I’m tired of reading on internet blogs and forums about how “ineffective” a by-pass filter system is on our old cars. I’ve even seen posts and comments from supposed knowledgeable mechanics that advise against adding back the by-pass circuit when doing rebuilds of engines that have them.<o:p></o>

I’ve got one of these systems on my 1950 Dodge Coronet, and all this “ineffective filter” commentary was counter-intuitive. Why did manufacturers add them? Cadillac, known for its superior engineering, used a by-pass filter on its new 1949 OV design, and did not change to full-flow filtration until 1962. Nevertheless, I wondered, “Is the filter on my car just an “appendage” that was added for marketing purposes, or does it really help to keep my oil cleaner?” After doing some research, I’ve come to the conclusion that not only is the by-pass system NOT ineffective, it actually is pretty effective, even if not as “good” as the full-flow systems that are standard issue today. Here is some good information on this Forum, from people who appear to be knowledgeable:<o:p></o>

http://forum.studebakerdriversclub.com/showthread.php?46568-62-64-Studebaker-V8-full-flow-blocks-versus-51-62-by-pass-filter-blocks-a-discussion<o:p></o>

An engineering friend came up with what I think is a good, non-technical common sense way to explain the effectiveness of by-pass filtering. He says to think of swimming pool filtration. That is essentially a by-pass situation, where a small portion of the pool water is drawn into the filter and then returned to the main (dirty) body of water. I’ve observed many times absolutely filthy black pool water, after having sat all winter, become crystal-clear and sparkling after 2 or3 days of by-pass filtering. I’d say that’s pretty effective filtration.<o:p></o>

So, IMHO, if your oil supply starts out clean and you have a by-pass filter, you will come out OK in the clean engine dept. The only time a by-pass filter may not be effective is if the oil becomes suddenly contaminated, such as if you were driving in a severe dust storm with an open-crankcase ventilation system. A full flow would get 99% of the immediate contamination on a single pass whereas a by-pass might take 30-45 minutes to remove it. A lot of damage could result in that time. But, under normal circumstances where we drive on paved roads, the chance of the immediate contamination is remote. <o:p></o>

I’ll stick with my by-pass filter, and I will continue to advise people who have no filters on their classic cars to add the by-pass circuit. Very easy to do, as opposed to trying to plumb a full-flow into a block not originally designed for it.<o:p></o>

By Pass filters are effective but full flow filters are more effective. The change over to full flow oil filters I believe coincided with advances in oil technology and the addition of detergents and modifiers. I've modified my 1929 Chrysler to a full flow oil filter and I use Castrol GTX oil. Now I know some of you have just rolled over in your grave, but the car has been on the road (the second time)for thirty years with no measurable wear in the engine.

Back in the late 1970s during my uni days I did some testing on the bypass filter and found that after 60 minutes of running time less than 50% of the oil had passed through the filter. That's why I changed over. Plus zero detergent oils were getting harder to obtain and more expensive. But that aside an engine doing 2000rpm goes through 60 000 revolutions in 30 minutes and that's a lot of chances for that little piece of contaminant to do some damage or get caught in the wrong place.

The other interesting point that gets brought up is "How do you know if oil is actually going through the by pass filter?"

The answer " You don't"

You could potentially drive your car for years with a blocked filter and have absolutely no idea.

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Studebaker offered bypass oil filters as an option in the 1920's. I'm sure other companies did, too. On my Dictator there are two places where a filter could be mounted. There are four evenly spaced holes in the firewall directly above the cylinder head for a rectangular filter as well as four threaded bosses on the right front side of the cylinder block. Mounting instructions were provided in the service manual. A sight glass was part of the filter piping. The pipes for the firewall mounted filter were rigid steel.

Terry

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"How do you know if oil is actually going through the bypass filter?"

Easy. After the engine is warm, feel the outside of the canister (side away from the engine block). If it is warm, oil is flowing through the canister.

I would question the 50% in 60 minutes result. If you look at the link I provided in the original post, you will see that a filtration engineer did some tests, and his results showed a much better turn than that. My own observation is that the oil flows through pretty quickly, a sad lesson I learned when I did my first filter change on my old Dodge and the gasket did not seat properly. Within about 20 seconds, I had about a 1/2 quart of oil on my garage floor.

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Bypass filters bleed off engine oil pressure. I think of a bypass filter as a loose or worn main bearing. In order to get a 15 minute 'full filtration' of the engine's oil, I believe you would see a slight drop in indicated oil pressure. If an engine has worn bearings, and excessive oil clearances, then a bypass filter might create a noticeable pressure drop.

As mentioned above, the best setup would be full filtration for 'the big stuff' and bypass for the smaller contaminants. Providing the engine has plenty of oil supply, that is a healthy oil pump, the amount of pressure drop should be minimal.

I certainly like the idea of all the oil being filtered, all the time. As opposed to some of the oil an any one time. The additional fine filtration from a bypass system will result in very clean oil, I had a bypass system [NOT toilet paper] in a Cummins-powered truck, and it had clean oil instead of black oil at 10,000 mile change intervals.

On so many old engines without full flow filtration, I see scored bearings, and see some rather amazing accumulations of grit and abrasive crud in the oil journals of the crankshafts. Engines that are full filtered usually don't have scored, damaged bearings, they have smoothly worn out bearings.

GLong

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I have a 32 PA plymouth no filter,,,the next model PB had a buypass,,,,,,in early 30s,, there was no detergent oil,,,,if there was any thing in oil it would fall to bottom of pan so instant filtering was not as imprrtant,,,,,,with the use of detergent oil all the crap is held in suspention,,,,the buy pass filters only a small amount at a time so any foreign thing in suspention will go to the bearings-----could cause trouble-------just had my motor rebuilt and the shop recomends no detergent oil-----------though the modern viscosity oil holds presure more evenly-------

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