Death Rattle and when erg blocked car almost dies.

Gasket Masters is using it. One advantage: its cure time is a lot longer. The application method they use in their videos seems sensible too.

there’s a couple of head gasket links in my signature; if on a phone turn it landscape to see signature.

 

I don't know if you've done one of these or not, butttt......
Did you get the 2nd part of kit? The one that has the oil filter housing "O" rings and the
water pump gasket and the front crankshaft seal? If not, do it! Or you'll be running to Toyota to
get them. Like I did.

I go their black sealent in the tube. I think I used less than half of it. And not leaks!
There are 2 little "O" rings I couldn't figure out where they went. One goes on the valve cover,
near the oil filler, and the other one goes on the timing chain cover the 10mm(head) in the lower third.

There is also a square "O" ring that goes on the cam next to the sprockets, next to the 3 section one.
It will probably stick to the valve cover. One of the guys couldn't find the right one, the other pulled up
the cam hold down clamp to find it.
If you take the 2nd from the spocket cam clamp off, and fold up two pieces of a paper towl too a 4 piece
section you can lay them across the cam and tighten the two "black" 10mm bolts down and it will hold
the cams in place. After you put the crank at the zero mark, and make sure the cams are in their respected
positions. It makes it really easy to put the chain on.

Don't forget the 12 point "triple square" head bolt tool, like I did! Autozone has it in a 4 piece set, you have to
look at the tools section to find it. It's $16. discount auto wants $30....

If you are going to do the valve guide seals, and you should. Make sure you get a spring compressor that is
small enough for the Prius. Mine was just a little too big and I was lucky to find a washer to fit over the valve that
the two teeth of the compressor was able to fit on. After you remove the spring, put the whole thing in a box or
jar so if the compressor slips, parts don't go flying off somewhere and you spend an hour or so looking for it.

I only had one valve, the intake on the #4 cylinder closest to the end of the head that leaked. But I seated them
all in. I have a bench grinder with a wired wheel that goes a good job of cleaning off the valve. Mine were pretty
nasty and I had to take my scraper the clean off some of the carbon the wheel couldn't get.

It sure runs a LOT smoother! And I gained 2-3 mpg!

 

Toyota specs 10 mm double hex. There is a difference. The double hex is available on Amazon.

 

Yeah, you can get the spec'd 10 mm double hex in a set like this one:

https://ctatools.com/products/9295

When people use the wrong tool, the wrong tool they usually use is a 12 mm triple-square. Triple square and double hex have the same number of points, of course, and the 12 triple-square kinda fits, but if you draw both you can see the triple-square is too pointy, and won't engage the sides of the head bolt recess as well as the correct 10 mm double hex.

 

A couple of cans of carb cleaner and brake cleaner.
Might as well clean the cooler and intake manifold while it's off.

Wait until you have the cam shafts holder off to do the exhaust manifold. Plenty of room
when it's out of the way. And then attach it before installing the cam shafts holder.

Take notes. Sandwich bags to put the nuts and bolts in, and label them.
Rubber gloves. Lot's of patients! Don't rush, take your time.
You don't have to take the injectors rail off. You disconnect that whitest plastic cover
then squeeze the two squares and release the fuel line.

Maybe take photos of what and where the cables are you disconnect.

 

3 cylinders look like the valves have been cleaned, big leak.
You really need to check that the head is not warped first. No point in doing
anything else if the head is warped, and how bad and can it be safely shaved.
Did you spray wd40 into the intake/exhaust ports and check if any of the valves are leaking?
If they are, you need to get some valve grinding compound and seat them in. Clean them off
very well with carb cleaner!
If they aren't leaking, you're okay. You should still do the valve guide seals, since you have them,
and you have the head off. 30 minute job. Just get a small valve spring compressor.

Clean clean clean! Clean the head and remove the old gasket material. Then check if it's warped.
If you have a metal ruler you can check it.
Clean the pistons off. Stick rags in the water ports so nothing goes down them.

It's probably best if you remove each valve, one at a time, and clean off all the carbon.
If you have a bench grinder with a wired wheel, it will be easy.

But most important, check the head for warpage...