Many site visitors appear to arrive with the pre-conceived opinion that some technologies because they are old, are outdated, obsolete and functionally replaced by newer technology.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.