I am planning to do a 13-hour 800mi return trip this weekend. So, as usual, I checked (car/engine completely cold) the tire pressure (all good) and fluids, you know - just in case. The oil level is ok, and then I check the coolant levels. The engine coolant is where is supposed to be. The inverter coolant is at "low". I checked the user manual and it is not where it should be. No lights on the dashboard. I "religiously" brought the Prime to the 6 months checks. The last one, at the 2yr/17000 mi mark, was done last February and fluids were marked on the report as "Checked and OK at this time". So now some the questions: 1) does inverter coolant "evaporate" over time and needs refilling, if ever? 2) are there any known inverter coolant leaks on the 2021 Prime (i.e., this Prime model version)? 3) did Toyota stealerships simply never even looked at it and always said "OK" when it wasn't, and what is in there is the same liquid from factory and "evaporated" in these past 2.5 years down to low? 4) can I buy any 50/50 ethylene coolant and top it up when car/engine is fully cold? any particular brand/color or I must get the Toyota one because "she is special"? (the user manual on page 605 states: " Only use “Toyota Super Long Life Coolant” or a similar high quality ethylene glycol based non-silicate, non-amine, non-nitrite, and non-borate coolant with long-life hybrid organic acid technology." Is this super special or any decent brand will do? I will refill, and check if in 2-3 weeks it goes down again. I don't think it is a new leak, I haven't seen any traces of anything anywhere in my garage or any light turned on or the AC doesn't work as expected. It is all good. If I didn't go on this trip I wouldn't even know the level was "low" in the first place. My next check is in August, they'll need to check it for sure and repair under warranty. Thank you.
If the level (cold) is at/on the Low mark, it's okay. Mine has been hanging out on the Low line for years. A few years back, it was maybe 1/4-inch below the low line, and I simply added some water to bring it to the Low line. It stays there consistently. The consensus on these Forums is to stick with the genuine Toyota pre-mixed brand. But as I said, if it is only down a little, I just add water.
Keep an eye on your coolant level. 2017-19 PPs are addressed in this Toyota Technical Service Bulletin. I'd think your 2021 is immune, but one never knows. https://static.nhtsa.gov/odi/tsbs/2019/MC-10166037-9999.pdf
About 5~6 years after purchase of our new 2010 Prius, both engine and inverter coolant levels had slowly dropped, to the low marks. I bought a gallon of Toyota Super Long Life Coolant (pre-mixed), topped both reservoirs up, and they haven’t budged since.
I went to a Toyota stealership and got a gallon of pre-mixed 50/50 coolant (the pink one) for $32+tax. That is 2x to 4x the price of "coolant" you find at the super market or at auto-parts stores. But...after your feedback and some research, I discovered that the color matters and the mix is well more than just ethyl-glycol and distilled water. And what Toyota wants, doesn't really match anything out there, or worse, some coolants don't even clearly state what they are or what are the "ingredients". Expensive, but I bought peace of mind. (I mean, a coffee at Starbucks is almost $10). I topped the inverter tank with probably a cup of liquid (so it was "low" but it clearly has a tiny circuit) and it has stayed there since my 800mi trip this past weekend. Could I have added a cup of distilled water? Probably, but I didn't know how much it would take to go from "low" to "max" - and it is really cold in Colorado, better not dilute it too much. Oil, another story and easier to get it right, even with non-Toyota branded supplies. In this case, I thought "let's not complicate my life".
