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Flathead six oil filter system

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  • Engine: Flathead six oil filter system

    My flathead 170 has the optional oil filter with a replaceable cartridge inside a housing that is bolted to the engine's cylinder head on the distributor side of the block. A small diameter steel line carries oil to the filter housing from the intake/exhaust side of the block; another line from the bottom of the filter housing returns the oil to the engine on the distributor side of the block. I assume the oil going to the filter is being diverted from one of the oil galleys, perhaps the one carrying oil to the cam bearings.

    Obviously, only a small fraction of the engine's oil is being sent to the filter through that tiny steel line, and what is being sent is a totally random sample. I'm wondering what the current opinion is on the usefulness of that stock filter and if there is a good option for a filtration system that filters much more of the engine oil.

    I know some people are going to say that any oil that gets filtered is better than none, but I have a feeling that None is just about the amount the stock system is actually filtering. Does anyone have any good information on the effectiveness of the stock filter system? Or does anyone have any good options for getting more of the engine oil filtered more of the time? Thanks.
    Last edited by dstude; 01-20-2019, 10:34 PM. Reason: typo

  • #2
    Search the site. This has been discussed several times before. But you are incorrect, all the oil gets filtered, just not every time though the engine. If you doubt the flow though the filter try forgetting to tighten the lid sometime...


    • #3
      The bypass oil filter filters about 10% of the oil at any given time. That being said, all of the oil does go through the filter and I agree with nvonada, don't get the cover on the filter tight enough or crimp the gasket and then you will see just how much oil does go through the filter at any given time. Ask me how I know about that. Bud


      • #4
        I removed a bypass oil filter unit from a 259 V8 to paint it and failed to tighten one of the ends of the flexible rubber oil line when re-installing. It came loose when I started the engine and almost emptied the crankcase before I got to the ignition switch to turn it off. The oil sprayed out at least 10 feet. The stains are still on the brick.
        Skip Lackie


        • #5
          All that you can do to improve your Filtering and Oil Condition is, change the Oil and Filter at 1-2,000 Miles or 6 Months.

          No one has tried to jury-rig a Full Flow Filter setup on a '39 to early '62 Six, but remember they only catch the "Rocks", if they did an efficient job of fine filtering like the Partial Flow Filter, the Bearings would be destroyed when they plug up.
          Second Generation Stude Driver,
          Proud '54 Starliner Owner


          • #6
            I remember my father talking about bypass oil filters years ago. He said that the bypass oil filter only needed to be replaced when after running the engine for a while, if the filter was only warm to the touch or cold, then the filter should be replaced. I still do that to this day because if a bypass filter is partially or fully plugged, the worst that can happen is there is no oil filtration. Full flow filters also have pressure by pass systems for the same reason. I agree with Rich, there is no reliable way to make a full flow oiling system work on an engine that is not designed for it. Bud


            • #7
              I continue to be amazed at the misinformation about bypass oil filters. They do work, and can work very well. While full flow filters do start to catch particles as soon as the engine starts up from the 100% flow of oil, you need to think about how well the filter had worked when the engine was last shut off. An engine that has been running for 15-30 minutes on a partial flow filter has very clean oil due to the continuous circulation. There should not be big chunks or many small particles when the engine starts up again.

              You can choose how efficient you want the cartridge to be by selecting the brand and type. What happens with a bypass filter is that some significant fraction of the oil always goes through the filter. Modern filters are 90-95% efficient at removing small particles down to a few microns in size. [5 microns = .0002 inches]. The filter that you want would be 95% efficient at capturing particles of 10 microns or greater. Unfortunately, oil filter manufacturers don't usually publish those performance numbers so you have to look for independent test data. You will have to pay more for a very efficient filter, but that is true for full flow or partial flow filters.

              Here's an example that might resonate with you. Think about a swimming pool with 10,000 gallon capacity, about 15 x 30 feet oval, 4 ft deep. The filter system pumps 25-50 gallons a minute through the filter, but it clearly takes hours to average even one pass for the contents to go through the filter, as some water is filtered and put back in the pool. If you start up the pool in the spring, the water could be dark and green. In some hours or maybe a day or so, it's crystal clear. If you run the filter every day for a few hours, the water stays clear. Don't turn the filter on and the water gets cloudy and green again. This is a partial flow system that works.

              Here are some graphs for an oil filter assumed to be 90% efficient (an average filter) is a partial flow system.

              Click image for larger version

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              Last edited by garyash; 01-21-2019, 06:54 PM.
              Gary Ash
              Dartmouth, Mass.

              '32 Indy car replica (in progress)
              ’41 Commander Land Cruiser
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              web site at


              • #8
                When I was involved with high performance Volkswagen engines years ago, one of the aftermarket companies that made high volume oil pumps for the air-cooled engines added another plate to the stack of machined plates that formed the stock pump body. (If you don't already know, air-cooled VWs have an oil pump that is accessible from the outside of the engine, much like a Studebaker six or a big-block Chrysler V8.) The newly added plate was installed next to the pump's gears and it redirected the pressurized oil through passages in the plate to a built-in horizontal boss that had been cast as part of the new plate. That boss was machined to accept a modern screw-on, full-flow oil filter (Fram, Wix, etc.). Once the oil had been pumped through the filter, it re-entered the oil pump to be distributed to the engine in the normal way. Nothing about the engine's internal oiling system was changed, yet the engine now had a full-flow oil filtration system on an engine that formerly had no oil filtration at all, other than a piece of window screen in the oil sump to keep rocks out of the pickup tube. All that was different was that all the oil that was being pumped was now being momentarily diverted to a filter, then returned to the pump. And all the oil got filtered every time before it re-entered the engine's oil passages.

                So anything is possible. I often think how nice it would be to have a similar plate added to a Studebaker pump, one that held a full-flow filter, just as an upgrade to help insure a longer engine life. It's just a thought.


                • #9
                  Gary, Skip and others commenting on this particular topic. My 59 Lark flathead also has a steel line from an oil gallery on the passenger side to the optional filter mounted on the driver side and another steel line from the filter assembly to the base of the oil filler tube. I am using a Baldwin B50 filter that has a spin on mount. Though I have not mounted a mechanical oil pressure gauge into this orfice it seems recently that the oil pressure is very low. From reading the manual it indicates that the clearance between the end of the oil pump gears and the cover plate is critical. I have changed the gaskets of this pump as the engine was rebuilt a number of years ago and was never started until recently but was continually turned over and the cylinders were lubricated. I don't believe that you can only assemble the oil pump one way so I cannot surmise that this has affected the oil pressure. The car has sat so very long that most of the gaskets were weeping. For a novice such as myself is there a method of pressuring this flathead? I don't believe that you can spin the oil pump like you can in a Chevrolet for example. Regards, Mark


                  • #10
                    I have a couple of flat head 6s and the oil pressure line is from the cam oil galley and the filter is supplied directly from the fitting on the oil pump. The oil pressure gage is dead ended so there is no risk of robbing oil from the cam bearings. With the appropriate restrictive fittings for the filter there is no risk of robbing oil pressure and volume.


                    • #11
                      Hello Altair I am also from BC. On my engine there are no fittings on the oil pump, it is plumbed just as I wrote above. Do I understand your reply that some of your flathead engines are fed to the filter from the cam gallery and another is fed from a fitting on the oil pump?


                      • #12
                        007 I am in Coquitlam 604 942 0490 On both of my flat head engines a 52 and 53 the oil filter is fed from the oil pump and the oil pressure gage is plumbed into the oil galley. I guess if your pump does not have an external fitting it would not be difficult to drill and tap one or get a later pump with the fitting. Dave


                        • #13
                          Click image for larger version

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ID:	1725186This is what it looks like, from the pump to the filter and from the galley to the gage.


                          • #14
                            What was the reason for filter placement on the head, rather than mounted to an inner fender? I would really like to move mine, thus improving distributor access. Is there any reason not to do this?


                            • #15
                              The engineers probably chose the cylinder head for the placement of the oil filter canister because it would be easy for gravity to drain the oil back into the pan through that fitting at the base of the oil filler tube. But certainly you could put the canister on the fender -- you would just have to deal with a long return line to the filler tube (or the side of the oil pan). If you do that, make sure the canister is mounted high enough, and the return line runs downhill enough, that gravity can do its job.