4th Gen DIY heat exchanger bypass solution

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.



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



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



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.

 

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.

 

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.

 

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.

 

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.