Coolant going down - no idea of cause

I had a 2017 Prius Two for 57K miles with no issue, but much of my driving was at highway speeds. I have seen people here doing a lot of city driving having the issue. Perhaps that relates. i only stopped driving my Prius due to a collision with a 4Runner.

 

From what I've read (mostly here) it's due to a defective batch of the Exhaust Heat Recovery components: it has an internal radiator with coolant running through it during warm-up, and it's been leak prone, presumably due to defective welds.

Later model years I think don't have the problem, though I think it dragged on a while, till Toyota "woke up". To date owners are having problems getting it fixed, due to dealerships, either due to ignorance or avarice, that misdiagnose as head gasket failure, and/or bill owners when Toyota would pay.

I suppose Toyota's fine with that (Toyota and the dealerships conveniently enable each other), and as well seems to be dragging their feet on production of the (expensive) replacement component, which includes catalytic converter.

And yeah, it does technically defeat a pollution control when owners do a bypass, and I'm sure both Toyota and the dealership would love to say it voids warranty.

 

2016 & 2017 cars seems to be the ones failing. I think the issue was resolved in the 2018 model year.
You technically aren't allowed to bypass it, because under CARB rules - that's defeating a "smog device component". If they catch you, you'll automatically fail smog and forced to go to a referee station for 'tampering' with a smog device.
I wouldn't preemptively bypass it, because of what's stated above and denying coolant flow to the heat exchanger will probably hasten it's demise. No coolant to prevent the hot exhaust gases from melting the welded joints.
Just pop the hood at every fill-up and take a glance at the coolant jar, probably check the oil too. It's a good habit to get into and will probably save you money in the long run - you'll catch potential issues early.

Hope this helps....

 

Fortunately, many of us are not in a CARB state where that would apply, As always, YMMV.

 

Maybe an extra 2 minutes

Does not matter as the flow is always going through the exhaust gas heat exchanger.

 

I can't see how the coolant bypass is "defeating a pollution control device" since you are not altering the CAT or the flow of exhaust gases in any way. That said, if this leak happens to me, I will likely just replace the CAT on my $ and call it a day. It takes long enough to get heat in the cabin on cold mornings as it is.

 

Just a data point, but I have a 2019 Awde, and was losing coolant. I kept adding coolant everyday for about 3 months, used about two gallons, no codes, temperature was in the normal range as monitored by Bluetooth dongle and a phone app. Finally got crazy with white smokes while accelerating, especially up hills. Got the bottom side bypass done a few days ago, I used a silicone hose since it’s so close to the cat. Also secured the flap to the straight flow through position on the exhaust. No more white smokes, coolant holding at the correct level, and the temperatures are not bad, it does run a bit cooler and takes a while longer to get warmed up, but it’s all good here.

 

The faster heating of the engine coolant allows the ECU to lean out the mixture sooner - reducing greenhouse gases. Toyota considers that assembly part of the CAT, therefore emissions control device.
The smog police failed one of my cars because of a patched hole in the air box. I think the previous owner was injecting propane or N2O through it. I had to get another air box from the junk yard. Just glad he didn't brand the car. This would've required me to go to a referee smog station at twice the cost and more in-depth look at EVERYTHING..

YMMV

 

Most states do not care if you bypass the exhaust heat exchanger or even the cat. In Texas this year they have abolished inspections. Safe, no. Good politics, yes.

 

Dear Lord I am so blessed I don't live in CA because this would drive me to walk up a tree.....