Updated Coolant Reservior With Radiator Cap

The "old" one looks exactly like the degas bottle system that came in with Gen 3 in 2010, with the single pressure cap on the bottle, rated for 108 kPa pressure.

The "new" one looks as if they have reduced the cooling system pressure (the rating on that cap is 88 kPa) and returned to a stagnant-backwater-reservoir system like Gen 1 and Gen 2 for some reason. They must have had a reason, and probably it's explained in the New Car Features manual.

 

You should NOT mess with this as it likely will have an adverse affect on the pressure retained in the cooling loop.......and that is important.

A really LOT of cars these days have the pressure cap on the "overflow" bottle and not on the actual radiator itself.
There is nothing wrong with that design.

Move on and find something else to worry about.

 

The change coincided with the manufacturers going from the old overflow-bottle systems to the newer degas-bottle systems, where the bottle fully participates in the coolant circulation and any air gets circulated back to it.

That 2021 picture looks like Toyota moved back to an overflow-bottle system for that model. I am curious why they did that; as soon as somebody looks it up in the NCF, we'll know, and until then ... we probably won't.

 

I'm really sceptical that's anything more than a policy change.

 

They could just be doing search-and-replace in the Owner's Manual. In third gen manuals they had exactly the same phrases, only the oil weights editted, thus:

 

there may be ongoing ring/piston issues they are concerned about

 

Reserve Tank Cap - Toyota (16475-28140),
rated at 108 kPa is still specified for many new Toyota vehicles including the Prius,

https://parts.mcgeorgetoyota.com/oem-parts/toyota-reserve-tank-cap-1647528140

 

The 108 kPa cap is still used on the inverter bottle in the Prius through 2022. It was used on the engine degas bottle through 2019.

The engine bottle for 2020 through 2022 is a reserve tank rather than a degas bottle, and the pressure cap 16401-36030 is used (with a plain plastic cap 16405-37020 used on the bottle itself, pretty much like grandpa's old reserve-tank systems). The spec of 88 kPa on the pressure cap can be read in the OP's second photo.

 

Correct. 2020-2021 Prius models now use a separate traditional radiator cap.
Cap - Toyota (16401-36030)

https://parts.mcgeorgetoyota.com/oem-parts/toyota-cap-1640136030?c=Zz1jb29saW5nLXN5c3RlbSZzPXJhZGlhdG9yLWFuZC1jb21wb25lbnRzJmw9MSZuPVNlYXJjaCBSZXN1bHRzJmE9dG95b3RhJm89cHJpdXMmeT0yMDIxJnQ9bGUmZT0xLThsLWw0LWVsZWN0cmljLWdhcw%3D%3D

Using the 88 kPa cap would result in lower pressure inadvertant release of coolant, since there is no intervening radiator cap.

If you use the 88 kPa cap, you'd need the radiator cap replace the radiator with
Radiator - Toyota (16400-37380)

 

So they switched back to an overflow-bottle system, and reduced the spec pressure to 88 kPa.

They did change the radiator, but it's not where the "radiator cap" attaches; that attaches to the "engine coolant pipe" seen right beside the overflow bottle there.

If you were doing a retrofit (which I can't think of any reason to do), you'd need the new bottle and "pipe". The old radiator has nipples at the top corners for use with the old degas bottle, which you would need to cap off (or switch to the new radiator). There is still a small upper nipple on the cylinder head water outlet, formerly routed to the top of the degas bottle, which you'd have to reroute to the top nipple of the "pipe" instead.

Again, I can't think of a reason to do any of that, but it would be interesting to learn Toyota's reasons for changing the design.

My 2010 is the first degas-bottle car I've ever had, and I have enjoyed how little coolant it ever loses, and how simple it makes the burping process.

I was surprised to find the degas-bottle patent (I think this might be the original one) was filed by Toyota in 1990. (It refers to some earlier Japanese "unexamined utility model publications", but this might be the first official patent filing.)

 

Maybe to meet either emissions or l/100km targets.

 

ANYONE KNOW WHAT THIS IS AND IT’S FUNCTION ? A COOLANT VALVE WITH A SENSOR ? IT ON DRIVERS SIDE ENGINE BLOCK…
I DON’T KNOW WHAT YEAR ENGINE THIS IS — see photo

 

It is an electrically-controlled "flow shutting valve" further described in this post and the article linked from it.

 

Super … si if direction of exhaust gasses won’t bad enough… someone added direction of coolant flow… (… holding on tight )