Weird Overheating Issue

If the system is bypassed I might expect it to turn on the check engine light since the heat exchanger is there for emissions and the temperature sensor is there to confirm proper operation.

Posted via the PriusChat mobile app.

 

I would get it up high enough to inspect it, measure the existing metal hose connection, decide if the two hoses are long enough to directly connect and then buy a hose kit like this $6 Amazon set or directly from an auto supply for a little more. If you need an extra piece of hose get it locally. Two vice grips could clamp off the hoses while you work.
Worse case your out ten dollars and you have some stock for the hardware drawer. Beats a $150 diagnostic at the dealer.

 

Seems to me that you probably have air in your system. Or a faulty thermostat.

 

The exhaust heat recovery system is all new to me. I am learning just like you are. The Exhaust Flow Control Valve is located inside the exhaust pipe.

Based on the flow diagram in post #25, I am guessing that the Exhaust Flow Control Valve is closed when the car is cold and the Exhaust Pipe Gas Control Actuator Rod is retracted. This allows the exhaust gas to be diverted through the heat exchanger and heats up the coolant which then circulates through the engine to heat the engine quicker. As the coolant increases in temperature, the rod on the exhaust pipe gas control actuator is extended and the rod is used to open the exhaust flow control valve. I have not physically looked at my car to see how this works, but you said in one of the posts that you observed that the rod on the actuator extends when the car warms up.

Take a look at your car to see if the rod on the actuator pushes a lever or is connected to a lever that would rotate and open the exhaust flow control valve.

I have been reading all the new threads in the Gen 3 section of this forum the last several years, and this is the first time that I can remember a problem like you have.

EDIT: See the first half of post #32 by ChapmanF. He says the manual tells you how to check the actuator and the valve.

 

You need something much stronger than a binder clip

 

Because the actuator is one of those expanding-hot-wax deals just like a thermostat, one of these "what happens when an irresistible force meets an immovable object?" questions comes up. As the actuator warms, its wax is going to expand and that rod is going to extend, unless something physically broke in the past and the wax burst its containment.

And if that rod is still pushing a lever effectively connected to the valve, the valve is going to open, unless it is so seized that the rod has pushed the lever off the shaft, or twisted up the shaft,, or bent the lever out of the way.

Those are the kinds of things I'd be looking for,

 

Apparently no codes based on a recent bypass.

It’s very likely the valve is caked with carbon since it is located within the exhaust.

 

I would be interested is seeing what exhaust backpressure is at the downstream O2 sensor port with the valve closed vs open. But not too many folk have the gear (as simple as it is).

Posted via the PriusChat mobile app.

 

Get it up to temperature so that the valve is open and clamp it or otherwise secure it open. I would do that first and bypass second if that was not enough. No binder clips.

 

From what I've read, it fails internally. I don't think it was welded correctly or well enough
and it leaks. A defect that I believe Toyota will warranty.
And ALWAYS filter the coolant if you're reusing it! Who knows what crap is in that system now.