2019 Prius Slow Coolant Leak

No. It might cost a little mpg. Toyota design it to open on high exhaust pressure alone when high rpms are being used.

There is no single root cause of gen3 head gasket failures unless you want to blame the engine design and testing team when it was adapted from a Corolla for use in a hybrid. It worked fine in a conventional Corolla which even had the egr system. The Corolla also had low tension rings which lead to excessive oil burning as did Camry and Rav4s but Corollas did not blow head gaskets without overheating.

It's clear Toyota quickly knew they had problems using the Corolla engine in a thermal cycling hybrid with an Atkinson cycle camshaft. Five years later a redesigned 1.8L solved the hg problems for gen4 which is why many have embraced using parts of a gen4 in a gen3 car, eg a Frankengine. Hybrid Pit now sells a rebuilt gen4 block, a modified head gasket and a gen3 head topped with a gen4 cam carrier. But most older gen3s are not worth using their most expensive option when fully rebuilt and moderately improved gen3 engines are available for less.

 

could the new cat be leaking?

 

Not intending to highjack thread- but wondering if @JeffPGH notices same thing- when I put coolant in the car in the morning, I hear a gurgling as if the coolant level is going to go down incrementally if I were to give it a minute, but it doesn’t appear to. Why is it that the right corner will appear as if it has no fluid but yet the left corner and the rear right clearly show that there is half way up the volume of the tank it would seem.

 

My 2019 Awde developed similar issue. I was adding coolant daily to top off for months, and then I saw that I would blow white smoke out the exhaust typically during acceleration on uphill drives. I did the bottom side bypass and locked the bypass valve to open position. The coolant level has not changed ever since. Try looking in the rear view mirror, during an uphill acceleration…

 

Everything that you've stated could also be an EGHE leak too. What tests was performed to verify it's a head gasket issue? Do you have a P0300 code stored? Guesses can cost you $3750 with no resolution to your current problem. The big elephant in the room is that your NOT working on a Subaru and it's a totally different engine design, so I don't see the relevance here. It sounds like your just trying to talk yourself into spending $3750 on a guess.....

Your car, your money - do whatever you like.....

 

You can't keep losing coolant every day or you will be stranded a hundred miles from home.

Assuming the engine overheated prior to the first exhaust heat exchanger repair, the current shop is probably right. With your level of coolant loss, and assuming he can smell gasses in the reservoir, he should be able to see coolant in the cylinder or at least view a "steam cleaned" piston. Or get a positive combustion gas in coolant test.

Is this the same guy who did the earlier borescope test?

This is the most compelling hg symptom you have observed and reported. Do you think you missed this on other occasions when you said the engine ran fine?

I still think an exhaust heat exchanger bypass (post 6) is SO easy and cheap - even as a diagnostic to absolutely rule out this possibility.

Overall, if it is a hg, your dealer was truly negligent if not grossly incompetent with their negative borescope test while missing something as obvious as combustion gasses in the coolant reservoir.

The next question is what exactly will the current shop do for $3750 to guarantee a hg repair will work on this engine which has been run hard with this fault.

 

Protracted neglect of a leaking exhaust heat recover (EHR) system can lead to a blown head gasket: when you're constantly obligated to check and top up the coolant engine may run dry in between your checks, and overheat.

There IS a TSB for the EHR system leakage, very prevalent with 4th gen, especially the earlier years. Dealership should have got on that right away, instead of all this malarkey.

For a Toyota dealership service advisor to suggest stop-leak is preposterous. I would get in touch with Toyota USA.

 

In post 1 the op reports the exhaust heat exchanger was replaced recently after a bypass proved it was the source of coolant loss two years ago. However further coolant loss began immediately which is when the dealer did a negative borescope and pressure test. At that point they suggested stop leak.

Obviously the dealer continually misdiagnosed the hg which resulted in a new exhaust heat exchanger. The bypass had been in place for two years.

 

Ah, ok. Maybe the replacement leaked too?