Head Gasket Info

Discussion in 'General Motoring' started by mutant_dan, Jan 14, 2005.

  1. mutant_dan

    mutant_dan Guest


    From: Gene Goldenfeld <genegold@h...
    Date: Thu Jan 13, 2005 8:06 pm
    Subject: Re: [outback] Head Gasket failure info on Subaruvanagon
    mailing list

    dyerlytle wrote:

    There is an interesting discussion about head gasket failure in 2.5L
    Subaru engines over on the subaruvanagon mailing list. (This is a
    mailing list for people with VW Vanagons who have swapped in a Subaru
    engine to replace the VW water boxer.)

    Indeed. In the interest of getting the discussion over here (and
    providing me a copy to archive), I've copied Al Wick's posts on head
    gasket failure from the Subaruvanagon group. I let him know.


    I was in unusual situation where I was able to find the head warp
    "gasket fail" problem before the dealers were getting any failures.
    Many years ago I adapted a new 2.5 (10k miles) to my airplane. I have
    sensors galore on the plane, so when the head first started leaking, I
    was able to look at the data on my laptop and see that the head leaked
    pressure to coolant system 3 seconds after I hit full throttle. It then
    dissipated 5 seconds later. I really learned a lot and deliberately
    operated at full throttle for long periods (hour or two). All the time
    logging the pressures and temps every few milliseconds.

    So here's the deal. All failures are caused by air in the cooling
    system. No air, no problem. If you have air bubble AND you operate at
    high throttle settings, the head will warp. It takes a long time to
    show up. So if there was trapped air 6 months ago, then you might now
    start to see discolored coolant, overheating. Or it might only occur
    climbing a hill in hot weather. Only the 2.5 has this marginal
    condition. All other Subaru's bullet proof.

    My flying partner makes a living replacing gaskets on 2.5's these days.
    Number one repair item. It appears that the 2.5 has an area at center
    of block/head interface which doesn't have enough coolant flow. When a
    bubble passes by, it boils locally. This eventually causes head to
    warp, gasket to give out. Subaru has tried 3 different style gaskets,
    even adding coolant conditioner to improve heat transfer. Still a
    problem. But absolutely all failures caused by trapped air in system.
    All models of 2.5 liter the same.

    The solution is very simple. Just drill and tap your coolant crossover
    pipe and add a fitting that allows air to leave engine and rise to your
    swirl pot. You will never have a problem. I operate my engine full
    throttle for hours at a time. Fabulous engine.

    -al wick

    I got a couple other private messages regarding the same. I'll try to

    The crossover tube is the aluminum coolant tube that lives under the
    intake manifold. It's rectangular in shape and the main coolant hose
    attaches to one end of it. It's the one everyone reverses. I'm unable
    to say there is a "best place" to add a fitting to the tube. Likely it
    does not matter where you place the fitting. Just somewhere in the top
    of this tube. The fitting needs to be on this cross over tube because
    this is the highest point in the ENGINE cooling system. Your goal is to
    purge any air that happens to be in the engine. This is different than
    purging air from your radiator or from your heater core. Air in the
    engine causes head warp. Air in other components just reduce their
    efficiency. We imagine that air flows with the moving coolant, but
    actually it only does to small degree.

    Drill and tap this tube. Install a fitting, and run hose from that
    fitting to your swirl pot. No dips in hose, it must gradually rise to
    swirl pot. As long as the swirl pot is above the engine it will
    automatically purge all air from the engine. This results in a "robust"
    cooling design. Robust meaning it handles unusual conditions. If your
    brother in law borrows your vehicle, blows a hose, and doesn't realize
    he needs to bleed air, no problem. Because your system automatically
    purges all air from engine.
    mutant_dan, Jan 14, 2005
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  2. mutant_dan

    racerxman Guest

    What is the "swirl pot" device talked about in the repair post letter date
    Jan 14 2005 at 9:42am, "Head Gasket Info."?

    Am trying to repair the cooling system on my 2002 Subaru Outback. I ca
    tap the crossover tube and install a brass nipple, add a small diamete
    radiator hose, and connect it to the " swirl pot", but do not know wha
    this is.
    racerxman, Jun 12, 2008
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