Finally the dreaded P0301 Code

Caution here: Toyota really did add a low engine oil warning in a later Prius generation, but a Gen 3 has no such thing. It only has the low oil pressure light, which only comes on when the oil is so low that it can't be pumped and the engine is eating itself.

In a Gen 3 (or earlier), it is important to use the dipstick and manage your oil level to make that light never ever come on.

 

Likely the cylinder walls are scored in area because of sticking oil rings....
Either add a short block, or purchase a remanufactured engine, maybe hybrid pit?

"IF" the cylinder walls are not scored, you could hone them out and then put the newer
pistons and ring in.

 

In addition to likely damage due to operating the engine dangerously low on oil.

 

A gen3 burning oil sends hydrocarbons to the egr before the cat has a chance to burn it. Gen4 takes exhaust to the cat first then the egr dramatically reducing hydrocarbons to a big egr. This is combined with improved pistons, ring, cylinder insulators etc.

An OCC tries to condense oil sump fumes before they get into the intake. A different circuit unrelated to the egr.

Bottom line: If you are burning 3.5-4 qts in 5k miles, enough to alarm on low oil pressure, you need a rebuilt engine. Which usually requires a better short block, used or new.

 

Did you replace the head gasket, or are you now in the process of doing it?

 

One work around is to upload somewhere else, say Google Drive, then link it here.

Do the tops of the cylinders pistons look relatively uniform? How's the head gasket look? Check in particular the wall between cylinders one and two (standing at front of engine bay, cylinder one is at left end)

 

The valves you can remove, since your going to replace the valve guide seals anyways... right?
And if you have a wired wheel on a grinder attached to a bench, you can use that to clean them off.
That's how I clean them. You can us carb cleaner to clean the ports.
BEFORE you remove the valves, lay the head flat and spray WD40 in all the ports. You don't need
a lot. Wait about 5 minutes can carefully raise the head and look to see if any valves are leaving.
If any are leaking you'll need some valve grinding compond and a drill to seat the valves in.
If you do one, do them all. It's not that hard and doesn't take that long.
Make sure you a smaller spring compressor to remove the keepers. They are tiny, do not lose them!!!

For the pistons, you can put a thin bead of grease between the piston and cylinder wall,
with the piston at TDC. And use a scrapping small pry bar and carefully scrape off the carbon.
Wipe it off with a wrag and brake cleaner or carb cleaner. Then you can lower the piston and clean
the grease away.

 

I would have the head inspected and reconditioned by a machine shop.

 

Yeah sorry, I did mean to say top of pistons. I’ve edited my post.

judging from your pics (), top of piston one does look cleaner, likely due to coolant getting in. Picture of head gasket clearly shows failure at adjoining Easley between cylinders one and two as well.

the rest of the head gasket looks not too far gone, which hopefully means you’ve caught it early enough that there’s no bent piston arms or breakage in the damper between engine and transaxle.

 

Be real careful with that kind of cleaning. Don't use a metal wire brush or metal tools. If you scrape the surface at all you can create a stress riser. You just need to get the thick buildup off, you don't need to get it clean enough to eat off of.

But I do applaud your effort

 

Brass bristle brush?.

 

They look new! Good Job!
How did you clean them? What did you use?

If you search youtube for "replace valve guide seals" there will be several videos
on how to do it. Make sure you have a strong magnet to catch the keepers....