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Bypass oil filters

by Ron Marabito

Editor's note: This topic ran as a Topic Of The Week (TOW) in the RV Forum. Tow leader Ron Marabito introduced the subject with an explanation of how bypass oil filters work and how they can be used to extend the interval between oil changes. Other forum members joined the discussion with their own experiences.

First I want to define what a By-Pass Filter is: It is a depth type filter that removes the smaller particles of contaminates that cause the normal wear within the engine.

Often the first question asked by the neophyte is: I already have a filter, so why do I need another one. The answer to that question is simple. Because the primary, or full flow filter, must filter all the oil passing through the engine on a full cycle and in order to do that, it can only filter down to about 10 micron size particles at best and not completely shut down the flow of oil due to being too restrictive. The By-Pass filter on the other hand is added into the system to filter particles down usually to about 1 to 5 microns in size to minimize wear on the engine. Some companies advertize down to 1/10 micron, but they get away with that only because they have managed to trap a few particles that size.

The reason the By-Pass filter is able to do this finer filtration is: It only passes a small percentage of the oil from the engine at any given time, at a much slower rate and in no way takes away any lubrication from the engine.

Put in its simplest terms, the By-Pass Filter is a on-board oil system cleaning tool. It is constantly removing contaminants from the oil. A good one eliminates Solid Contamination, Moisture Contamination and Condition Caused Contamination which includes: Oxidation, Nitration and Acid Formation.

I personnaly believe in them and have used them for many years. Unfortunately, I do not have one on my coach at this time due to lack of space anywhere near the engine. If I go ahead and install one, it will have to be located in a compartment at least 10 feet away from the engine. It will work fine during the running cyle but will have difficulty draining down to the sump when the engine is shut down. This causes difficulty when trying to change the filter. This filter must be installed higher than the oil level in the sump to drain by gravity.

The single most significant benefit of the use of the filter, coupled with a proper preventative maintenance program, including oil analysis, can allow you to run your equipment for life without ever changing oil again. I went 50,000 miles without an oil change on my last coach. The current owner has put 30K to 40K on it since and it had more than a quarter million miles on it when I sold it. Now I know this will get some action from the doubters.

Experiences of forum members

Bruce Alter
I have a dual filter system from bypass filter and one regular filter. Installed it on my 2002 F250 diesel about 3000 miles ago when the truck had 30000 miles. Also switched to AMSOIL synthetic at that time. Just replaced the normal filter and took an oil sample for analysis today. All I did was replace the quart I lost when I changed the filter. As long as the oil analysis comes in OK, I intend to go extended range on the oil without changing it. The standard oil analysis is $20 with an additional $10 charge for another TDN test for extended use. With both filters, the oil is filtered to less than 1/10 microns....much more than the standard filter of approx 4 microns. The info is available on the AMSOIL website . The lab I am using for the oil analysis is Blackstone Labs

Ron Ruward
Oil analysis is a very good practice even if not doing extended oil changes. With a good synthetic oil the bypass filters are great. We had a car we bought used while living in Montreal with 40K miles on it. I installed Amsoil and at the next oil change I installed bypass filter and new Amsoil. for the next 120K I changed the Bypass filter twice a year. WHen we sold the car it had 180+K. The car was driven another 60 or 70 K by the folks I sold it to before they sold it. The car may be still running for all I know. The only problems we had with that car was related to the rust caused by all the salt they use on the road in Montreal area.

I wonder how many folks are aware that the Fleetgauard 900x series oil filters used on Cummins engines have a baypass filter built in. The lower approx 1/4 part of the filter is a bypass filter. I have only seen a cutaway filter. It may not be as effective as some of the systems using a separate bypass filter but should be bettter than just a plain full flow filter. As I understand it the bypass portion is not full flow but just passes a portion of the oil going through the filter through the bypass section.