Air bubbles in 2012 toyota prius coolant system

You might not have this as they removed it after a certain year but I am not sure when.

 

2012 model year that coolant bleed valve I think is gone, but you could still temporarily pull off a top hose right there (it’s highest point in coolant circuit, while adding more coolant, giving air in the system an escape route.

what’s the miles on it?

 

What are your reasons for thinking so, and have you tried simply following the repair manual method for filling the coolant?

Your 2012 has a degas-bottle style of cooling system. The extra headspace in the plastic reservoir is where the air should end up when you're done.

The procedure starts by filling the reservoir extra full (up to the line marked B). Then you put the cap on, start the engine, and run it all the way up to operating temperature (this can take a long time) and then several minutes more, during which you can squeeze and shake some hoses.

Then shut the car off and wait for everything to cool down and contract to the surrounding temperature. Look at the level of coolant in the reservoir; it should have traded places with the remaining air in the system, and dropped from B down to FULL.

Some early cars had the extra valve you probably saw in the YouTube video. Toyota dropped that later, and when they dropped it they did not add any extra steps in the repair manual, no undoing hoses or anything. They simply took out all old mentions of fiddling with that valve. They left the procedure for swapping the air into the degas bottle, unchanged.

 

Right here:

 

I’m suspecting chaps being clever, posted a white pic?

anyway, wouldn’t hurt to pull this one while adding coolant, might allow some air to escape, then reconnect it, once coolant starts flowing out.

grabber tool tip at the hose:

 

Where and when are you seeing these bubbles? Actually seeing them makes this the most direct evidence here. Do you see them all the time, or only when the coolant reaches a certain temperature?

That observation is less direct evidence, as it mostly just reflects that "air bubbles" is something people often say when they don't know why a car is overheating. Sometimes a wider net has to be cast to find the cause.

As there is only so much air that ever could be trapped in the system, you would eventually stop seeing bubbles once they all arrived at the degas bottle (as long as you never let the bottle get low enough for its bottom hose to suck air).

If there are bubbles that just keep on appearing as long as the engine is running, they could be bubbles of something that isn't air, maybe exhaust from a damaged head gasket.

Someone attached the updated repair manual instructions for coolant replacement here (though the illustrations didn't survive, for some reason, the steps are there):

https://priuschat.com/attachments/2011-prius-engine-coolant-replacement-pdf.68950/

 

Those are the updated instructions for all gen 3 liftbacks.

Just once normally does it. Be sure you notice that step (e) is to put the cap on the bottle, and step (g)(1) is to run up to temperature and then several minutes longer. (g)(2) is to do some squeezing and shaking of hoses. Step (h) is to check the final coolant level, but only after everything contracts and cools back to surrounding temperature.