Issue getting air out of Coolant System 2012 Prius no bleed valve

do some more googling. iirc, there are lots of threads with good advice on getting the last of the air out.

if nutz hada bleed valve, yours should too

 

You could pull off a hose where the the bleed valve was, atop the EGR cooler, achieve the same venting function. Just a little messier. Leave it disconnected while topping up the reservoir, squeeze hoses a bit as you go.

Have you ever cleaned the EGR (Exhaust Gas Recirculation) circuit and intake manifold (in particular the EGR passages in the latter)?

 

The 87251-47020 Joint, Water, No. 1 does seem to have come in a couple different versions over the years, one with the air relief spigot, one without. My 2010 happens to have the spigot there.

Either way, whichever version of that joint you have, you still have the overall degas-bottle cooling system design, where the dedicated hoses (shown blue in this picture) extract the air from high spots at the top corner of the radiator and at the cylinder head outlet, and deliver it to the top of the bottle where it belongs:



The extra spigot that's (sometimes) on Joint No. 1 is handy, because the location of that joint is in a sort of upside-down U shape of hose above the EGR cooler, so there'll be a bit of air there as you fill.

As to how much difference that makes really, I can't say. One clue is that Toyota themselves don't seem to think the spigot is essential in that spot.

You can find PriusChat posts that make it sound as if the mere presence of a bubble in a hose somewhere brings the circulation of coolant to a halt. Maybe that's an opinion carried over from human anatomy lessons about the danger of an air embolism in blood vessels.

But a big difference is the pump in blood circulation works by pulsing, so if there is an air bubble somewhere that just compresses on every pulse and re-expands, that really is bad news for circulation.

But all of the water pumps in a Prius work by continuously moving the coolant, and I suspect if you could replace the black hoses at that inverter-U spot with clear ones, you would see that the small bubble there just gets eventually carried away in the normal flow, finds its way to the degas hoses and back to the bottle, spigot or no spigot. I do not think the pump is likely to be ineffectively spinning in air either, as its location is pretty low in the system.

Hence I'm beginning to think that "oh, any amount of trapped air will explain that issue" might be an explanation that gets reached for here sometimes when probably something else is going on.

I've never gone out of my way in special magic dances to burp out the system, for what it's worth; no flogging the engine up steep hills or anything.

The manual says to fill the bottle to B, put the cap on, warm the engine to operating temperature, let it circulate that way for several minutes, shut it down, let it cool, and verify that the bottle level dropped from B to F.

The difference between F and B in the bottle is the amount of air the engineers expect to be caught in the system, and if the (cold) level has dropped by that amount, the air removal happened as designed. It's the procedure I've always followed and in my experience it just pretty much works.