Can someone help me wrap my head around how the frick these cooling systems work?

Can someone help me wrap my head around how the frick these cooling systems work? Why does coolant constantly flow *through* the expansion tank and what's the advantage of this system compared to a regular "hot coolant expands, spits into tank, cools down, sucks it back in" system?

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  1. 2 weeks ago
    Anonymous

    Overcomplicating relatively simple systems with proprietary electronic parts that are prone to failure with the marketing guise of techmology
    =
    Easy money in OEM part sales

    Just look at electronic power steering and a bunch of the garbage in modern vehicles

    • 2 weeks ago
      Anonymous

      They've been doing this shit since the fricking stone age, and many other European brands like Volvo have been doing it since the 90s

      • 2 weeks ago
        [PLEBSPOTTERS] BigC

        >90s
        my 85 Volvo 240 had it, I pulled over on the side of the highway in the middle of the Mojave desert to piss and I heard a hissing sound and thought it was my tires
        checked all my tires and they were all fine, opened the hood and the coolant reservoir was cracked and leaking out steam

  2. 2 weeks ago
    Anonymous

    because...because it just does! nah but really it's to be able to reverse the flow to warm up oil when the engine is cool

    • 2 weeks ago
      Anonymous

      As in because the coolant gets hot quicker it's used to help heat up the oil quicker than it otherwise would? Why would that not work in a typical open loop cooling system? Just needs a heat exchanger, no?

      • 2 weeks ago
        Anonymous

        I've only owned and worked on european cars, are most others able to reverse the flow of coolant?

        • 2 weeks ago
          Anonymous

          Reverse flow? please expleen

          >90s
          my 85 Volvo 240 had it, I pulled over on the side of the highway in the middle of the Mojave desert to piss and I heard a hissing sound and thought it was my tires
          checked all my tires and they were all fine, opened the hood and the coolant reservoir was cracked and leaking out steam

          Man even longer than I thought.

          > what's the advantage of this system compared to a regular "hot coolant expands, spits into tank, cools down, sucks it back in" system?
          Do you think the expansion tank is what cools down the coolant?

          >Do you think the expansion tank is what cools down the coolant?
          No, as the engine gets up to temp and the coolant expands and pressurizes, some of it goes into the expansion tank. When you shut it back off and the engine cools back down, the partial vacuum sucks it back out of the tank and into the cooling loop. It's nothing more than an overflow tank.

  3. 2 weeks ago
    Anonymous

    > what's the advantage of this system compared to a regular "hot coolant expands, spits into tank, cools down, sucks it back in" system?
    Do you think the expansion tank is what cools down the coolant?

  4. 2 weeks ago
    Anonymous

    VAG expansion tank is designed to fail to generate revenue for the dealers.
    they have yet to fix the design to reduce cracks/leaks.

    prove me wrong.

    • 2 weeks ago
      Anonymous

      As a vag tech I can't begin to tell you how accurate your post is. I've probably replaced hundreds of those shitty expansion tanks

    • 2 weeks ago
      Anonymous

      As a vag tech I can't begin to tell you how accurate your post is. I've probably replaced hundreds of those shitty expansion tanks

      i believe it is also known as "the VAG orb of death"

      • 2 weeks ago
        Anonymous

        This one leaks more than the orb of death. I frequently tell my customers, hey, this one's got a crack starting to form, let's get this replaced, the ones that listen avoid the trouble. The ones that don't come back not too long after with coolant warning lights. When I was being trained I was initially trying to sell coolant changes but the guy training me was like: don't bother, you change the coolant when it leaks. I thought he was being cynical but he's right. They all fricking leak

        • 2 weeks ago
          Anonymous

          Is it just VW using garbage plastic or do all these closed loops have this?

          • 2 weeks ago
            Anonymous

            It's related to thermal cycling stresses due to distance to the engine, most cars don't have a problem because the tank isn't 8 centimeter from the cylinder head so no and no.

          • 2 weeks ago
            Anonymous

            Nah, it's just the Germans. I rarely of ever see issues with other manufacturer's expansion tanks

          • 2 weeks ago
            Anonymous

            i wonder if it's because of what

            It's related to thermal cycling stresses due to distance to the engine, most cars don't have a problem because the tank isn't 8 centimeter from the cylinder head so no and no.

            says with the coolant overflow being so close to the exhaust side of the engine. i only just saw in my toyotas that the coolant bottles are quite far from the hottest parts of the engine.

          • 2 weeks ago
            Anonymous

            Nah, it's just the Germans. I rarely of ever see issues with other manufacturer's expansion tanks

            The NC miata also has an expansion tank that becomes yellow and brittle in 10+ years and should be changed. I grabbed a new OEM one for $70 and changed it myself. Should be good for another 10 years at least.

            So yeah, other cars have this issue too.

          • 2 weeks ago
            Anonymous

            so it seems like it's dependent on what the manufacturer specifies in regards to the type of plastic used. pretty sure my overflow bottle has been in thee car for at least 30 years, it's a bit yellow, but still going strong, not brittle at all. i'm tempted to buy a new one though because DAtism.

  5. 2 weeks ago
    Anonymous

    Modern coolants turn acidic when exposed to the air, with an expansion tank the idea is to keep the coolant a sealed system

  6. 2 weeks ago
    Anonymous

    Old style coolant reservoirs are just a simple overflow/fill access point, they were not properly sealed units (most had absurdly simple plastic caps, the same part used on the windshield washer tank) and the water in the coolant would evaporate over time through them, which required filling up as much as two quarts a year (depends on use, age and your area's temps) with distilled to keep it balanced and full.

    "Modern" coolant systems, the tank is now the pressure-cap sealed, regulated part of the system, there is practically no evaporation over time, which makes it easier to maintain.
    >wahh my plastic bottle cracked
    99.98% of the time that's an issue caused by the owner or some idiot mech overtightening the bolts or being a total hamfist when doing other work.

    My buddy at work has an '02 imapal 3800. Old style coolant reservoir. He didn't know these cars need to be checked at least twice a year. Now he has air in his coolant system (sloshing sound when starting up and sometimes turning).
    The "new" type of pressurized flow/return reservoir prevents this from happening compared to the old simple overflow tank.

    threads over OP you've been answered let's all move on.

    • 2 weeks ago
      Anonymous

      I did assume it had something to do with longevity but wasn't sure how it contributed exactly. Thanks anon.

  7. 2 weeks ago
    Anonymous

    Alright so it's done to make the coolant last longer, but *how* is it routed? Why does the coolant constantly flow through the reservoir? As far as I can tell you could just put a different cap on an overflow tank, eliminate the traditional radiator cap, and get the same result.

    • 2 weeks ago
      Anonymous

      It isn't necessary to make the coolant flow through the expansion tank constantly. But if you do that, you get a system that automatically bleeds itself.
      Only the amount of coolant that flows through the small diameter bleed hoses is what flows through the expansion tank, so not a lot. Picrel is how VW does it in their EA288 diesels.

      It can be done without the bleed hoses and without coolant flowing through the expansion tank, but then you need some way to manually remove air from the system. For example PSA thought the extra hose is too expensive for their shitboxes, so you get ports with little valve stem caps that the mechanic has to open to let air out of the system.

      • 2 weeks ago
        Anonymous

        That makes sense. One thing I'm wondering though is why if the supposed benefit of this system is that the coolant can't evaporate, I on my open loop cooling system have never had any issues with evaporating? I've never had to top up my coolant even a drop for any reason other than the system self-bleeding after having changed it. What gives?

      • 2 weeks ago
        Anonymous

        It's not just VW, all car makers use plastic cooling system components. Even Mustang, all brands, there are zero brands making all aluminum (other metals) cooling systems. Plastic and rubber only.
        I had to replace my bleeder line from expansion tank to the upper radiator fitting where the hose meets the radiator (the top red line on diagram).
        The rubber and plastic hose broke at the fitting on the expansion tank, only lost small amount of fluid but still got air in the line.
        There is a Process on these cars to bleed air. Loosen the bleeder screw off the exp tank, connect new hose. Go in car, no feet on pedals, hold start button 10 seconds and you'll hear elec water pump kick on, and you can hear fluid traveling in the system if quiet garage, do not start car! Go back to engine, top off till fluid drips from bleeder screw and tighten after you see the fluid drip.
        Be sure and check each model method, mine is BMW but I bet its similar method. Air in the system will cause pump cavitation.

  8. 2 weeks ago
    Anonymous

    You can either purge air from your cooling system by allowing the excess pressure to flow into a separate unpressurised container, from which the coolant is then sucked back from, through a straw, once the engine cools and the coolant retracts again.

    Or you can purge the air from your cooling system by utilising a SWIRL POT (just like the swirl pots used in fuel sustems and oiling systems) which allows the air to rise to the top, giving a constant feed of un-aerated coolant at the bottom.
    The swirl pot has a fill level below the top because some air is necessary at the top to be compressed and allow for the expansion of the coolant.

  9. 2 weeks ago
    Anonymous

    you have a blown head gasket

  10. 2 weeks ago
    Anonymous

    coolant doesn't flow through the expansion tank. its there for one reason. Expansion, when the fluid is hot.

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