I am going insane - 2012 Gen 3; please help.

Well you answered your own question about head gasket. If you know you have a problem with the head gasket, all the other things you mentioned are just symptoms. You should check if you have enough coolant in there and the coolant cap is tight.

 

Sounds like you've got an air bubble in there.

Might also have a gasket issue making the bubble worse, but you should be able to get back to where you were.

 

Air bubble. Sounds like a big one. Squeezing the radiator hose while it's running can help push the air through the system. But it'll take a while. Keep an eye on the reservoir and make sure it doesn't get too low and make another bubble.

 

@NutzAboutBolts video does not use the same fill procedure as the repair manual. The latter recommends to fill to the “B” line on reservoir, install the cap and run in maintenance mode.

FWIW, I followed the video too, no issues. I did leave the vent open while filling (vent on early 3rd gens, incorporated in temp sensor junction, just above EGR components), had no issues. But maybe just lucky.

 

How FAST did you refill the tank?
I've done it 3 or 4 times on my Prius, and have never had a problem.
I think the most important part is to fill SLOWLY! Very slowly.......
Poor a cup or two, then wait. Repeat, repeat, repeat....
Once the tank starts to fill, start squeezing the lower radiator hose.
Then fill slowly again. When the tank is filled to the "B" mark, start
squeezing the upper radiator hose, and hold it for a few seconds each time.
Once the level stops going down, ready the Prius, and let the engine run until
it shuts off. Turn the Prius off.

Clean up and put all your tools away. Check the level and add to the "B" if needed.
Then drive the car for 5 minutes or so close to home making sure the engine is cycled
several times.
Then park it on level ground and
give it 10 minutes and check the level. It will probably be right at the seam.

I've only done this at least 100 times on several cars and only once or twice have I ever had
air in the system.

 

Did you note the coolant level before draining?

I followed the Toyota method as @Mendel Leisk kindly shared and didn't have any issues, level dropped from B to Full perfectly, (no valve for air release available, and I found it impossible to reach/squeeze the radiator hoses).

I didn't even use proper Phosphate enhanced coolant, but mileage is only 35k mi currently, (forgot what it has back then).

Contrary to consensus here in PriusChat I have bottles of K-Seal waiting to be added at the first indication of coolant loss. (Have used it on my wife's Panamera). I do follow instructions carefully...

 

K Seal? No No No. Don't do it, you must resist!

 

Really not a lot of extra arm clearance there.

 

Maybe drain into a clean container and reuse?

with 2012 you probably don’t have the aforementioned bleed valve. Just for giggles you could pull off one of the topmost hoses (at hose junction just above EGR components) and leave it disconnected while filling, till coolant comes out.

 

On the other hand, Toyota added no such instruction to the refilling procedure, when they revised that tee to be without the valve; they just removed the steps where you'd fuss with the valve.

 

I've watched a Toyota video of them vacuuming out all the air and forcing in the coolant.
I guess that's the way they do it. All you need is that $10-20,000 machine!

 

You can get a UView AirLift for under $150.

I used that technique once. I didn't find it enough of an improvement over the procedure in the manual to justify dragging out the compressor and paraphernalia to do it that way again.

You can't do it partially; if you didn't get a complete flawless fill on the first try, you can't just try again. As the vacuum collapses the hoses, the coolant from the first try will be slurped and sprayed out the venturi. So if you line up all the dominoes just right the first time, happy day, else you drain and start over.

 

Good diagnoises and trouble shooting work!

 

Maybe the fuse is just the “messenger”? What’s the miles? <134k.

The engine coolant pump has a propensity to fail, best replaced by 150k at latest. Thermostat too. < It’s time.