4th Gen DIY heat exchanger bypass solution

Discussion in 'Gen 4 Prius Main Forum' started by texasdiver, Jul 28, 2022.

  1. texasdiver

    texasdiver Member

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    For those of you who have been following my saga. About two months ago I started to encounter massive clouds of white smoke from my 2016 Four Touring and started to get the coolant overheating light going on. The car was also going through coolant. the entire coolant reservoir would be drained in 5 miles.

    Not knowing any better I immediately thought "head gasket" and brought it to my local indy mechanic who aren't Prius experts but they are pretty good. They also diagnosed head gasket and started to itemize the $4K plus bill it was going to take to fix it from machining the head to all the labor. But poking around here on the head gasket thread I was warned to check the heat exchanger first. Which is just some sort of coolant piping built into the catalytic converter. I went back to the mechanic with the Toyota info bulletin on this subject and they confirmed it was the heat exchanger not the head gasket by following whatever diagnostic procedure Toyota had specified.

    So now I was down from a $4K head gasket repair to a $1K catalytic converter replacement since the heat exchanger is part of the catalytic converter. HOWEVER the 4th Gen catalytic converters were on national backorder and no one in Washington could find one. My mechanic also informed me that it was illegal for them to install a used one, even if I could find one, and that there are no authorized after market part for the 4th gen catalytic converter. They also told me that they could not rig up any kind of bypass as that was not an authorized Toyota repair. The dealer told me the same thing.

    This meant that if I was going to drive the car anytime soon I would have to rig up my own bypass. I did this using an assortment of PEX plumbing hardware to create a brass U to route one hose back to the other hose and then wired the whole thing up to the frame so that it wouldn't flop around. This worked but I was unsatisfied with the result but the car drove fine on local errands for a month. After doing a lot of searching online I finally found a u-shaped bypass hose that fit and re-did the whole thing to create a permanent solution. I will probably just leave it like this permanently as the car is garaged and we don't have a really cold climate.

    The correct bypass hose to buy is the Gates 18777 Premium Molded Heater Hose which you can find on Amazon here. You want a hose with 5/8" opening on each end:


    There are a lot of other coolant bypass hoses all over Amazon as this is apparently a common thing on some American trucks but they all have a 3/4" hole one one side and a 5/8" hole on the other side and won't work here. The first one I bought I had to throw away after figuring this out. Don't buy this one:


    Once I figured out the correct hose I bought the plastic 12-ton Rhino ramps at AutoZone which just barely fit under the front cowling of the Prius after buying and returning the larger metal ramps from Harbor Freight. With the front wheels on the ramp I further jacked up the driver's side and put jack stands there to give myself more clearance and installed this bypass hose. It might as well have been designed for this exact purpose because the fit was perfect and I re-used the spring clamps from the old hoses. Here is what the repair looks like. I think I will just leave it like this permanently. It doesn't trigger any alarm codes so whatever sensors there are in this system are upstream of this spot. I left the metal intake pipes on the catalytic converter uncovered. I figure that won't hurt anything. They are designed to have coolant in them so a little road spray in winter won't hurt anything if they get some water inside.

    [​IMG]

    Here you can see the two intake pipes on the catalytic converter

    [​IMG]

    In the pictures it looks closer to the catalytic converter than it really is, and is in the same exact place as the old hoses used to be. These are the two hoses that I removed which appear to be made of the same material and gauge as the gates u-shaped hose that I replaced them with

    [​IMG]

    That is it. This is actually a very simple repair once you figure out what to do. Just have a container ready to catch the coolant because about 1/2 gallon will drain out as soon as you remove the first hose.
     
  2. robsnyder20

    robsnyder20 Active Member

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    Unbelieveable, great write up and post. Hard to believe a $6 part caused basically the car to be down two months. Glad you were able to get it fixed without a replacement. I'll be doing the same exact thing if unfortunately I find myself in your shoes.
     
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  3. Jburner

    Jburner Member

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    Great write up and huge savings if this happens to mine as well. No way am I paying to have a new cat put on if it’s just the heater. I can wait a bit longer for heat.

    It almost looks like from the picture of the hoses you took off that one of them could be used in a pinch as a recirc hose if bent around in a “U” shape.
     
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  4. Mendel Leisk

    Mendel Leisk Witness Leader

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    I think the repair is free. Toyota has acknowledged the defect. Main issue though:

    They can't get the replacement exhausts. It'll happen eventually, but just for the interim. I really think there should be an exception made, that Toyota dealerships would be allowed to do the (temporary) bypass. The current impasse is a joke.

    Maybe they'll get on applying for such an exception, if they tick off enough enough customers that new car sales start to suffer. Oh I forgot: they don't have new cars.
     
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  5. texasdiver

    texasdiver Member

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    I couldn't get Toyota to acknowledge it when I called the dealer here in Vancouver. They claimed there was no warranty service bulletin on this topic for my particular model and so therefore, it would be at my cost. The car is 6 years old and has about 100K miles. I didn't argue or elevate the issue higher up the chain because I knew they didn't have any parts anyway so I needed to find a different solution than wait on Toyota whether or not they were going to pay.
     
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  6. texasdiver

    texasdiver Member

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    I couldn't get Toyota to acknowledge it when I called the dealer here in Vancouver. They claimed there was no warrantee service bulletin on this topic for my particular model and so therefore, it would be at my cost. The car is 6 years old and has about 100K miles. I didn't argue or elevate the issue higher up the chain because I knew they didn't have any parts anyway so I needed to find a different solution than wait on Toyota whether or not they were going to pay.
     
  7. texasdiver

    texasdiver Member

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    If you try to bend one of the existing hoses it will kink and likely block the flow of coolant. So better idea to just buy the right hose. You can get it overnight from Amazon or possibly at local auto parts stores if you know the exact hose you are looking for.
     
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  8. CR94

    CR94 Senior Member

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    Uh ... If coolant was leaking into the exhaust, then can't exhaust leak in the other direction into the original coolant pipes that you left open? Then you have a (small, so far?) exhaust leak under the car. I'd plug those open pipe ends.
     
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  9. texasdiver

    texasdiver Member

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    I suppose that is possible. They aren't under any pressure or anything so any ordinary plug of any sort that won't fall out would do the trick. Probably an ordinary 1/2" rubber expansion plug.
     
  10. CR94

    CR94 Senior Member

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    They're under about the same pressure as a small hole in an exhaust pipe or muffler would be. Your rubber plugs might need to be more heat-resistant than the original hoses, because the pipes won't have relatively cool coolant flowing through them.
     
  11. J Laz

    J Laz New Member

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    Hello Texasdriver!! Hope everything went well with the fix! This you notice anything out of the normal.
    Thank you for the info from the write up good luck!
     
  12. ChapmanF

    ChapmanF Senior Member

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    Just in case anyone reading later is wondering, the heat exchanger and the catalytic converter are both built into the front exhaust pipe, but they are separate things.

    gen4fp.jpg

    The catalytic converter is one lump, the next lump is the heat exchanger, the one after that is a resonator or sub-muffler.

    Knowing the difference might not be super important as Toyota will only sell you the whole front pipe with all three things in it, but it's still helpful for understanding what's going on. Also, some aftermarket manufacturers might sell replacements for just a portion of it.

    There are really two catalytic converters in the car, but in Gen 4 the first one is part of the exhaust manifold, not part of the front pipe.
     
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  13. Mambo Dave

    Mambo Dave Active Member

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    I love it. Have you had the catalytic as hot as it can get to test if the hose will melt?

    I'm thinking that the hose should have a insulative foil wrap on it to reflect certain forms of heat to protect it.

    ------

    My other fear would be leaving the coolant holes open on the cat. Yes, coolant - a non-corrosive and stable water-based solution goes through those hoses, but road salt, and water with road salt from winter driving, may not be so kind to the internals of the cat. There is a chance that corrosion would eat it out from the inside I would gues.
     
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  14. Mambo Dave

    Mambo Dave Active Member

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    Car exhaust is pressure.

    It is also very, very hot. A rubber expansion plug on any part of the exhaust, but especially the most hot part of an exhaust? At this point it's seeming like you believe that the catalytic is bypassed. Did you bypass it, or will it still reach 750 degrees F?

    I'm just guessing here, but the longevity of the hoses on the cat's lines was probably from coolant running through them. There is a chance that, without coolant, they wouldn't have been able to stand up to the heat. I haven't' been under your or my car enough to know, but in your picture the hose on the left looks like it has extra material on it either for rubbing against something, or it may be for heat protection.
     
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  15. Doug McC

    Doug McC Senior Member

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    Helpful information, thank you. I have a question that might help us with newer cars and much lower mileage: “How often did you change your coolant and did you have it tested for ph?”
     
  16. CR94

    CR94 Senior Member

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    Condition of the coolant might not matter, if the leak is due to a fatigue crack, or to corrosion through the exhaust side of the metal separating coolant from exhaust.
     
  17. Mendel Leisk

    Mendel Leisk Witness Leader

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    Could the coolant bypass be more upstream?
     
  18. Doug McC

    Doug McC Senior Member

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    True, but those are significant “ifs” and it might be from the coolant side, thus the answer would then be helpful to some of us. If it was from corrosion on the exhaust side it would seem to be a strange coincidence that it is a problem at that same location for multiple cars and not appearing elsewhere on the system, wouldn’t it?
     
    #18 Doug McC, Oct 18, 2022
    Last edited: Oct 18, 2022
  19. Doug McC

    Doug McC Senior Member

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    I did some checking and while I couldn’t verify it 100% it seems that the exhaust system is stainless steel which, in my experience with other vehicles, drastically minimizes the chance of rust through from the outside, leaving the only option a highly unlikely stress crack. This increases the odds that the problem begins with internal corrosion.
     
  20. GasperG

    GasperG Senior Member

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    Long time no posts from me, because Prius just works :) but sadly it doesn't anymore :mad:

    It was loosing coolant (gen 4. - 2017), took it to the dealer and of course heat exchanger on the exhaust. New part costs €1800. In Europe we have 10 year waranty, but it doesn't cover the exhaust system. The service guy will write a claim anyway as it's not just simply exhaust, but no promises.

    So fingers crossed, will know in two days. New part is already ordered and arrives in the middle of February.

    Are there any other drawbacks to bypassing heat exchanger other than the obvious slower heating? I mentioned bypass to the service guy, but he mentioned something about air purging or something, don't know if he even knew hat he was talking about.
     
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