Coolant going down - no idea of cause

Check your VIN on the NHSTA site for a recall. There was a recall die to losing coolant in the exhaust heat exchanger. Continuing to drive the car can ruin the engine. From what I have seen here, the replacement parts tend to be backordered.

Here is the TSB, I think. https://static.nhtsa.gov/odi/tsbs/2019/MC-10166037-9999.pdf

 

For bloody years now...

TSB: Coolant leakage at front exhaust pipe (Prius & Prius Prime) | PriusChat

 

Search the forums. Tons of threads on this issue.

 

@Mendel Leisk can verify, but the TSB may still apply under your emissions warranty.

 

Wouldn't hurt to print out the TSB, bring it in, see what they say. Choose a day when the sales department is busy dealing with customers, and talk like Jimmy Stewart. Talk about lemon laws and loaner cars.

 

it's not a recall, but there is a service bulletin if a customer complains.
tsb-coolant-leakage-at-front-exhaust-pipe-prius-prius-prime.211059
the coolant leaks into the exhayst at the exhaust heat exchanger near the cat.
it's a big expensive job to replace the offending part, if you can even get it.
many here opt to bypass the heat exchanger by disconnecting the lines and tying them together with a piece of radiator hose.
4th-gen-diy-heat-exchanger-bypass-solution.234801

 

Toyota combined the Exhaust Heat Recovery System with the catalytic converter, so one expensive chunk.

 

God no, just research bypass. Google this:

4th gen prius exhaust heat exchanger bypass

Yields good results, including multiple PriusChat threads.

Amayama has it, I'm seeing $1548 CDN, with TBD for shipping. They say they'll get back to you with shipping charge before you need to commit.

Exhaust pipe for Toyota Prius ZVW50L - Genuine parts - Amayama

 

see post #8. you need to replace the part or do the bypass. if the coolant gets too low, you'll blow the engine.
fill the coolant and keep an eye on it all the time until you do one of the repairs. leak sealer won't do anything but ruin the radiators.

 

yes, just don't let it get low again

 

No an engine is about $8k. A bypass is $50.

 

You need to check coolant level everytime before you start the car - Not just daily. Until you get an idea of how much is leaking per miles driven. @rjparker stated $8K for engine replacement or $50 to bypass the exhaust gas heat exchanger. You'll need to get it fixed before your next emissions/safety inspection, depending on what your state looks for on those inspections.

Hope this helps.....

 

There was never any recall, just the TSB that explained the symptoms to look for and remedy (replace the forward CAT with the heat exchanger). You're out of the parameters for Toyota to replace it via the TSB, so you're on your own. A mechanic will not be able to diagnose without tearing into your exhaust to look for signs of coolant burn off. As long as you have unexplained coolant loss, possible poor cabin heating and maybe white smoke from the exhaust, you've got the heat exchanger leak. You don't want to run out of coolant and overheat your engine. Then you're dead in the water I'm afraid with a really expansive engine replacement.

The easiest thing to do at this point is the bypass procedure that takes the heat exchanger out of the equation. There's a simple U-shaped rubber hose that will do the trick in the vicinity of the coolant line connections near the CAT/heat exchanger. Here's the item on Amazon,

 

Since checking the coolant level for a few days now, how much is it using per day?

After you finish checking under the hood, put your prius in Ready Mode and keep the engine running
( turn on the defroster with heat ) or ( find the procedure to put the Gen 4 Prius in Maintenance Mode - so the engine stays running).
Now go to the back of the car and look for smoke from the tail pipe.
If you see any smoke, reach under the car and smack the muffler a few times to see if hear any sloshing in there, if you hear it and see it, that's coolant in there.

 

Does putting it in B also stop the engine from turning off; I forget.