Coolant change

Yes, just do them both at the same time. And yes, you leave the radiator cap off and keep and eye on it and refill as the air bubble come out. Also keep the overflow tanks filled up to the top Full line as it sucks some down. Some folks will even have the front on jacks to help purge the air from the system but it's not mandatory. (I don't)

I'm no expert on the Gen 3'd but for the Gen 4's, when running in Maintenance Mode, you just have to wait for the electric radiator fan to turn on twice and then you know it's fully warmed up/purged. (Takes about 20 minutes.)

I heard of this thing years ago and glad I have one....really helps refill the radiator as you bleed out the air...has adaptors that work on almost all vehicles.

 

Yes, just do them both at the same time. And yes, you leave the radiator cap off and keep and eye on it and refill as the air bubble come out. Also keep the overflow tanks filled up to the top Full line as it sucks some down. Some folks will even have the front on jacks to help purge the air from the system but it's not mandatory. (I don't)

I'm no expert on the Gen 3'd but for the Gen 4's, when running in Maintenance Mode, you just have to wait for the electric radiator fan to turn on twice and then you know it's fully warmed up/purged. (Takes about 20 minutes.)

I heard of this thing years ago and glad I have one....really helps refill the radiator as you bleed out the air...has adaptors that work on almost all vehicles.

 

If it's a 2012 liftback and you're following the repair manual, you put the cap on. The system reaches operating pressure during the warmup that way, so any trapped air pockets are squished to ½ size and travel more easily back to the degas bottle, where they trade places with the extra coolant you added above FULL to the B line.

Many people prefer to deviate from the manual by leaving the cap off, and they report doing it that way works for them. Without taking a position on that, I'll just say I've stuck to Toyota's way and it works for me.

This is specific to the Gen 3 liftback (and I think the v wagon also), but not the c. Although the liftback and wagon went to a degas-bottle system (Gen 1 and Gen 2 used reserve-tank systems), the c still uses a reserve-tank system from what I've seen, so in a c you would still use the old-style process.

 

With the engine coolant change, I left the cap off (following @NutzAboutBolts YouTube video), but next time I'd defer to @ChapmanF: I'd overlooked the "put cap on" instruction in the repair manual.

Aforementioned YouTuber's videos are worth a watch though; I'd say with the inverter coolant change they're pretty much by the book.

Personal experience with engine coolant change: I ran the engine in maintenance mode for about 30 minutes, fans never came on, I gave up and shut it down. Seemed ok anyway.

Also: repair manual says to open the petcock on back of engine to "drain block". In practice I found it very difficult to get to, and I got maybe 1/4 cup of coolant. I wouldn't bother with that. You might get a good amount disconnecting one of exhaust heat recovery coolant hoses; they're down very low. I looked at them, but chickened out: they're pretty beefy, thought I'd let sleeping dogs lie.

 

I've never used a fixed number of times for the fan or anything like that. As you can see in the repair manual section Mendel attached, they just say "Warm up the engine until the thermostat opens. While the thermostat is open, allow the coolant to circulate for several minutes."

You could interpret "several" as four to five, or maybe a couple more, depending on your favorite meaning of "several".

You can also see it says to set the heater for "maximum hot", but also the blower speed to low. Setting the blower any higher will just make the warmup take longer, which is already the slowest part of the whole business. Letting it circulate several minutes after warmup is ok, but waiting half an hour to get there? I'm an impatient sort, would drive me nuts.

I tend to race the engine a bit to get there faster. Of course, "race the engine" in a Prius is kind of a murky concept, as it's throttle-by-wire and nothing you do at the go pedal directly races anything. But it turns out they did program a little Easter egg into the ECU where if you're in Park and you press on the go pedal, it will say "oh, I'm in Park and the human is pressing the go pedal, I'll humor him and bump the RPMs a little." It's not a lot, but it's enough to bring the warmup time down to something I can manage to endure.

They also say to feel the lower radiator hose to know when the thermostat opens, but I just sit in the seat with my foot on the pedal and watching the temp via OBD.

 

You can also look at the coolant level. It will go from B to just below/at the full line. Got to love the engineering work to calculate that….

 

Maybe they just:

1. Filled it quite full and put a mark on the level.
2. Ran it till warmed up, put a second mark, where the level had dropped to.
3. Repeated several times with various test cars to confirm.

 

That is how you confirm you got the job done ... but check after everything's fully cooled down again, because it's all expanded when it's hot.