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Fuel filter: Before or after the fuel pump??

Discussion in 'The Hokey Ass Message Board' started by Tugmaster, Aug 22, 2010.

  1. Tugmaster
    Joined: Jul 20, 2005
    Posts: 2,824


    I ordered my new carbs from Tom Langdon for my 250 straight six last week. While I was talking to Tom on the phone the topic of fuel filters came up. I mention that I had mine mounted on the frame rail just before the fuel pump. He said having a filter mounted before the fuel pump was a very bad idea and that I was asking for trouble. He explained that the way a fuel pump works that it will cause vapor lock.
    I've ran my car in some very hot weather and have not had any problems. If it aint broke it doesn't need fixin. But.... Could I at some point have problems.
    Where are you guys running your filters? Before or after the fuel pump? Thanks, Todd
  2. pitman
    Joined: May 14, 2006
    Posts: 3,334

    from Hampsha

    Maybe run a screen before, and a filter after the pump?
    Keep them cowl-tank born rust flakes at bay?
  3. Gotgas
    Joined: Jul 22, 2004
    Posts: 5,723

    from DFW USA

    I prefer to have at least a screen to keep large debris like tank rust out of the fuel pump. If you have a clogged filter before your pump, I suppose you could have issues with vapor lock or fuel starvation, but at least you didn't run a bunch of trash through your pump. :)
  4. J.Fishbeck
    Joined: Nov 6, 2009
    Posts: 2,946


    I have always used Fram G3 filters, before my pumps. I haven't ever had any problems with vapor lock. Kept away from any heat, I don't see how that could cause any problems.
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  5. sixinarowjoe
    Joined: Aug 10, 2002
    Posts: 337

    from eastcoast

    no probs here -i run them before and after the fuel pump -keeps my holley webers nice and clean
  6. 1941ihkb5
    Joined: Feb 19, 2009
    Posts: 339


    Most of mine have filters before the pump. No problems so far...
  7. sixinarowjoe
    Joined: Aug 10, 2002
    Posts: 337

    from eastcoast

    dont think your gonna have a prob with your 6 seeing as the fuel line is on the opposite side of the exhaust manifold
  8. tommy
    Joined: Mar 3, 2001
    Posts: 14,738


    Mechanical pump on the pre-filter.
    Electric fuel pusher pump at the rear...a filter to protect the pump.
    It's worked for me for all these years. That's the way the factories did it.
  9. TexasHardcore
    Joined: May 30, 2003
    Posts: 4,724


    I always use two filters, one before the pump, one after. I change them everytime I do an oil change. Cheap insurance I guess. Never had a problem mechanical or electrical. I always use the clear plastic Fram fuel filters.
  10. shortbed65
    Joined: Feb 20, 2009
    Posts: 204

    from ne Ill

    I've read more than once - suck with a screen - push with paper
  11. fleetside66
    Joined: Nov 20, 2006
    Posts: 1,791


    I have one before & one problems (sbc with a standard mechanical fuel pump).
  12. canman
    Joined: May 6, 2010
    Posts: 112


    Pressure differential is pressure differential. As long as the system is insulated from heat where the filter is should not matter. In this case atmospheric pressure is pushing the fuel to the pump,the filter is just part of the trip.
  13. superiorslots
    Joined: Jul 19, 2010
    Posts: 316


    I'm looking at my Holley Electric Fuel pump instructions and it say's before the pump.

    I think I will take Holley's advice...I think they may have some experience in the matter.
  14. 39 All Ford
    Joined: Sep 15, 2008
    Posts: 1,531

    39 All Ford
    from Benton AR

    When pressurized, a liquids boiling point is raised, (like a pressure radiator cap).

    It only stands to reason that when suction is placed on a liquid, the boiling point is reduced.

    Toms point is that a flow restriction imposed by a clogged, overly restrictive, or undersized filter would cause reduced pressure between the pump and the filter and make the car more susceptible to vapor lock.

    This may not ever play out in practice for some (or even most) cars, but in some instances I am sure it will ring true, especially with todays gas.

    IMO common sense says screen before pump, filter after, another reason for this is that pumps make pressure more effectively than they draw fuel.

    (Atmospheric pressure AND displacement apply to pump theory).
  15. 39 All Ford
    Joined: Sep 15, 2008
    Posts: 1,531

    39 All Ford
    from Benton AR

    Holley is trying to avoid warranty issues created when a piece of debris takes out their vane pump, this is "their problem", vapor lock is YOUR problem... things ain't always as they seem.

    Detroit uses a screen before the pump and a filter after, both a blown pump AND vapor lock issues are "their problem" under warranty.
  16. walrus
    Joined: Oct 3, 2005
    Posts: 512

    1. 1940 Ford
    2. HAMB Old Farts' Club
    3. shoe box hambers

    I have always run a filter before and after the pump , mechanical or electric , in addition to a manual electrical cut off for the electrical pump , Mainly for saftey in case of a mishap or accident and it also works secondly as an anti-theft device, thief can't go far on a carb bowl of fuel.
  17. fab32
    Joined: May 14, 2002
    Posts: 13,982


    Most cars have a sock filter in the tank to take care of the big stuff. If I'm building a project I always replace this "sock" filter. Then if I'm running an electic pump I install a high flow filter BEFORE the pump and a high flow inline after the mechanical pump/ before the carb/s. On a drag car use one of the large capacity Fram filters right out of the tank and before the electric pump.

  18. dirty old man
    Joined: Feb 2, 2008
    Posts: 2,502

    dirty old man

    Carter also voids the warranty on their electric pumps without a filter before pump. I've set mine up with an AFCO stainless prefilter capable of handling race cars on methanol, 100 GPH @100 micron, then carter pump, then Fram HP-1 with replaceable paper pack filter, 90 GP @ 5 microns,then Holley pressure regulator, and then 2-500cfm Edelbrock 4bbls.
  19. Deuce Roadster
    Joined: Sep 8, 2002
    Posts: 9,522

    Deuce Roadster
    Member Emeritus

    I bought a small 12 Volt Carter replacement electric fuel pump from Car Quest a few years back. Sort of a universal fit type. 5 or 6 pounds of pressure. It had a small fuel filter built into the pump. It was on the side the fuel entered. They sold replacements for the filter also. I replaced the filter about every 4 or 5 thousand miles ... because I had a 60 year old fuel tank that to my knowledge had NEVER been out of the vehicle.

    Never had a problem ... :D

    I also had a small A/C brand fuel filter at the carb.

  20. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 3,479

    from Union, NJ

    I've always run a filter before the pump, and generally one before the carb too. I have a Holley Blue mounted next to the tank, and a Fram canister style filter before it, then an in-line filter under the hood. Been thousands of thousands of miles with no fuel delivery issues with that configuration
  21. neverdun
    Joined: Oct 17, 2007
    Posts: 554


    Mount it before the pump. No pressure on the filter with a small inline filter befor the carb.
  22. 48 Poncho
    Joined: Jul 24, 2005
    Posts: 694

    48 Poncho
    from Tennessee

    I put a filter before and after the pump. Mechanical pump Chevrolet 350.

    48 Poncho
  23. carbking
    Joined: Dec 20, 2008
    Posts: 1,670


    When we used to sell Carter electric fuel pumps, the pumps came from the factory with a short piece of hose and an inline filter on the INLET side of the pump.

    Joined: Jun 3, 2005
    Posts: 4,982


    Those Fram canister types are easy on fuel flow and have a good sized cleaning volume. More volume = less flow problems. If you can gravity-feed the filter all the better. Always a small one on the carb side. Inline broze filters are nice too. Get big ones for hi perf systems and again gravity-feed and easier to hide.
  25. Steve-Cook
    Joined: Jul 22, 2007
    Posts: 488

    from Garner, NC

    If you had a filter before the pump and it got clogged could it cause the fuel pump to become starved for fuel and damage it?

    I can understand a screen before it but I would think you would want your filter after it.
    Last edited: Aug 22, 2010
  26. ironpile
    Joined: Jul 3, 2005
    Posts: 915


    Wouldn`t the engine quit running and prevent damage?
  27. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 3,479

    from Union, NJ

    All the crap from your tank getting ground up and run through the pump will cause damage to it, hence the filter before it. If the filter is so clogged as to prevent all flow through it, the engine will die soon thereafter
  28. Steve-Cook
    Joined: Jul 22, 2007
    Posts: 488

    from Garner, NC

    I was thinking electric fuel pump that would continue to run similar to newer vehicles with an electric pump in the tank with a screen and then a filter after it my mistake.

    What is everyone putting in their tank other than fuel to get so much "crap"?

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