4th Gen DIY heat exchanger bypass solution

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.

 

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.

 

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.

 

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.

 

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.

 

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!

 

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.



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.

 

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.

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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.

 

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.

 

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?”

 

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.

 

Could the coolant bypass be more upstream?

 

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?

 

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.

 

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

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.