Jump to content
  • entries
  • comments
  • views

Old Technology Doesn't Always Mean Obsolete Technology!



Many site visitors appear to arrive with the pre-conceived opinion that some technologies because they are old, are outdated, obsolete and functionally replaced by newer technology. Case in point are two common forum topics, oil bath air cleaners and bypass oil filters. Both these technologies have been around for many decades and in fact perform better than the "newer" technologies of full flow spin-on oil filters and paper air filters. Let take a closer look at both. 

I ride and wrench on dirt bikes and quads for fun. I mostly ride in the California coastal mountains, noted for dry, hot and very dusty conditions. All my machines use oil soaked foam air filters because they are more effective than paper filters. When our cars and trucks were first sold dirt roads were the norm, not the exception. Chrysler used the most cost effective solution of the day, oil bath air cleaners. They provide very effective cleaning and unrestricted air flow. They are easy and cheap to maintain. So why would you want to change to a less effective and more expensive paper air filter? Most common reason is they are a lot of maintenance and the oil spills out of the pan and into the carb. Both reasons are not very good! Back in the 40's and 50's vehicle owners drove on a lot (including the occasional oil/pcp waste oil covered) on dirt roads and you needed to maintain oil bath air filters on a regular basis. Today we just drive on pavement. I personally have seen the air filter oil go two years in service and still have clear clean oil in the filter pan. The extra maintenance argument doesn’t hold for today’s use. I have driven mopar flatheads since 1968. I have never seen a properly serviced oil bath air cleaner leak oil into the carb or on the engine. If yours puked oil over the engine then you overfilled the air cleaner oil pan. Pretty simple solution to that problem! And don't forget oil bath air cleaners do a better job of feeding your engine clean filter air than a paper filter while being cheaper to maintain. One for old tech!

Now lets move to often maligned bypass filter. This is the source of so many incorrect internet myths the conversation becomes funny. "They only filter part of your engine oil..." or "Look at how small the piping is, how can it clean all the oil" and "It take forever for all your oil to go through a bypass filter". The best myth is full flow spin on filters do a better job of filtering than bypass filters. None of the above statement are true. First a brief explanation of how a bypass filter works. Your oil system is a closed system under pressure created by the oil pump. Oil circulates through the engine in the oil gallery. You can see the galley running along the driver’s side of the engine. This pressurized oil flow provides lubrication to main, rod and cam bearing so the journals actually "float" on a thin film of oil so they don't overheat and fail. This pressurized oil system also has a safety valve in case oil pressure gets too high, the oil pressure relief valve. The bypass oil filter taps into the oil gallery and dirty oil is piped to the bypass filter under pressure. (The same pressure your see on your oil pressure gauge). It is then filtered and readied for return to the oil pan. Bypass filters actually filter much smaller particles than full flow spin-on filters. Full flow filters are plumbed to directly feed oil to the mains and they have to pass high volumes of oil or the bearing will fail. As a result they can't filter to the same degree as a bypass filter. When the clean oil exits a bypass filter it goes back to the oil pan via the pressure relief valve. The pressure relief valve acts as an oil traffic cop, that is, if the engine oil pressure is high enough the pressure relief valve opens and clean oil flows back to the oil pan. If oil pressure is low, like at idle, the valve stays shut maintaining minimum safe engine oil pressure bypassing clean oil return from the bypass filter setup. Now lets address a couple of the myths. Think about how often your engine runs with minimum oil pressure. That is the only time clean oil is not returning to the oil pan from the filter. Basically anytime above idle and your bypass filter is working. What about those skinny oil lines, they can't move much oil, right? Wrong! The oil in moving under 20-60 pounds of pressure. On my B1 I once had a cracked (not broken) oil return line. I lost over 3 quarts in about 45 seconds. Based on that measure I thing it is safe to say all engine oil is being filtered every couple minutes the engine is above idle.

Modern full flow filters for modern engines must be able to pass large volumes of oil to provide full lubrication for mains and rods, plus have a bypass when the filters are dirty and clogged. They just don't filter dirty oil as well as a bypass filter. Bypass filters are still used extensively on long haul trucks, plus their are many aftermarket kits to add a functional bypass filter setup to modern engines. Why? They do a better job of filtering then a full flow filter!

Lastly, what about those remote mount kits for using a spin-on filter instead of the stock bypass system? They basically replace the bypass filter with an easier to change spin-on filter. My question is why would you want to replace a very efficient bypass filter with a spin on that typically allows particles 3 times larger to be returned to the oil pan? 

Like I said, old technology doesn't always mean obsolete technology! And if your engine doesn't have a bypass filter setup we have used units for sale in the P15-D24 Store. They also show up on eBay all the time.


Recommended Comments

The filtering system for air might better be called the oil trap filter rather than the oil bath. Most folks are probably under the impression that the air traveling into the engine passes through the oil, and the air is bathed of dirt as it passes through.  This is not the case.  The air flows into the cleaner assembly and passes through an oiled filter media.  What particles that are not trapped by this media travel at a high speed through the filter air path.  The air traveling at speed is forced to make a 180 degree turn changing direction from downward to upward over the oil reservoir.  As the impurities are heavier than the air they are suspended in, they can not make the turn and fall into and are trapped by the oil.  Engine heat and air flow keeps the upper media element moist with oil.  The major reason for maintenance other than cleaning out the accumulated entrapped particles, is to keep the oil at the level necessary to to supply the mist to the upper filter element.  If the system doesn't work well why is it still in place in most heavy duty construction vehicles, stationary diesel installations, and other equipment meant to operate in dusty environments?

Link to comment

As a result of this blog: I'm going to put my oil filter back on my truck and keep the oil air filter for the car. My truck air filter was left in the bed for 17 years and rusted out, so it has a filter in it now. With our dustless roads in CA, maybe I don't need an air filter. . .

Thank you for this information.

Link to comment

I think it was the lower hood lines of the late 50's and early 60's and larger displacement engines that killed the oil bath air cleaner, there simply wasn't enough room for a big tall filter on top of the big v8's that were being produced at the time. It wasn't a matter of replacing old technology with new but an example of form over function.

Link to comment

Well there were changes in the manifold casting on the L6, from earlier till later that big lump of cast iron under the car got shorter and shorter.  Probably why the later ones, 52-56 or so all have trouble with gas percolation.  So you are correct about lower hood lines and the change over to disposable paper elements.

Link to comment

I'm still trying to find the factory option oil bath air filter for my Sweptline. They work just fine, and the "what the heck is that???" factor is priceless... Car show folks who've never seen a stock engine...


Want a good debate? Alternator versus generator -or- 6v versus 12v...I was going to go whole hog 12v with alternator and power everything... Probably going to stay 6v and just replace the cracked door glass and add a screen to the cowl vent. There's another good argument, keep the cowl vent as issued, add a screen to keep out critters, or weld the sucker up solid...

Link to comment

Srcreen.  I was out and about yesterday with the temps in the low 90's.  That vent moves a lot of air around, and air that's moving is better than air that ain't when its that warm.



We could get the whole points versus electronic thing and just what do those letter" HEI" really  stand for??  I bet some folks are gonna a be surprised..............

Link to comment

Definitely keeping the cowl vent, always chuckle at the owners who let the shop "shave" it during the build process.


Points are better, all you need is a dime and a matchbook to reset them in a pinch.


HEI? Pretty sure it stands for "bad engineering" with fragile connections and a horrible, almost impossible to set attachment method of cap to dizzy. Could just be the V6 on our C10 though...

Link to comment

In 10 yrs, I put 10k on the odometer on my '48 B1B...recently I emptied the original oil bath air cleaner and put the oil in a glass pickle jar to observe what might be floating in there.  The oil was a little darker than fresh oil, and there was some crud at the bottom of the oil bath, but that was it.  And I drive on a fair share of dusty back roads and cattle pastures.  On a couple of occasions, I misjudged the pasture I was driving thru & caught a li'l air, so the oil bath sloshed a tad, and on one occasion, I forgot to tighten the ring clamp and that first right turn spilled most of the contents onto the engine.  I like the idea of the paper element conversion cuz it would not have been as messy as these spills, but I'm gonna stick with the oil baths on the flatheads...I've even got a conversion I'm testing that routes PCV gases into the original oil bath air cleaner housing :cool:

Edited by JBNeal
Link to comment

Lets add some more old technology that has seen a comeback


P 15 style Starter button on dash recently reintroduced as push to start key less ignition


trunk mounted brake light comes back as high center mounted stop light


Vacuum wipers come back as intermittent and infinitely variable wiper switch.


Old Lockheed brakes and wider modern all season radials DBA anti lock brakes


And one that is missing that should definitely come back adjustable front vent windows.............

Link to comment
Add a comment...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.

Terms of Use