Does my 2012 Cylinder #1 look OK?

Crosshatch is still there, like most. The small vertical lines don't look significant. Why is there moisture (water/coolant?) in the cylinder?

Is that the right sparkplug or is that a gen 3 plug you're using, it looks like an SC16HR11?

Gen 2 Denso should be an SK16R11

I hope like crazy you're not using that gen 3 plug in your gen 2. Holy F.

SK16R11 gen 2 thread is 14mm and reach is 19mm
SC16HR11 thread is 12mm and reach is 26.5mm

 

Are all the pics of cylinder one? Could you post pics of the other piston tops for comparison?

what’s the miles?

EGR ever cleaned?

 

Is engine coolant level stable in the reservoir?

What prompted your inspection, knocking? During cold-starts or it varies?

Head gasket failure is very common by your miles, with noise being due to uncompressible coolant pooling in the cylinders. The noise is "somewhere" along the drivetrain, often the damper between the engine and transaxle breaks spring, so that might be the source of the noise, but not the culprit, just the outcome of pistons and crankshaft struggling to compress coolant.

 

You have a head gasket problem. Coolant is leaking into one of the cylinders, and this is causing misfires, which causes the metallic rattle from the damper plate that is located between the engine and transaxle.

Classic Prius Gen 3 head gasket problem. There are hundreds of threads in this forum concerning head gasket problems with the Gen 3.

 

Wouldn't a damaged cylinder be just as expensive or more expensive to repair than a head gasket???

I've only seen damaged cylinders (cracks) on diesel engines. Prius will usually bend rods or punch a hole in the side of the engine, before cracking a cylinder.

 

Obviously your mechanic does not know the severe rattling caused by a gen3 head gasket induced rattle.

There is no need for the damper springs to fail to hear that severe metallic rattle. If the damper did break the noise would not go away.

The questions are:

1. How much oil does it burn?

2. Has it overheated?

3. Has sealer been used?

4. How much has it been driven since symptoms started?

Those answers would help determine if a hg is warranted, a replacement rebuilt or JDM engine should be used or the car should be replaced.

Virtually every gen3 hg fail does the same thing.

Coolant low usually means this has been going on for months.

 

It's a pretty common issue on the gen3 Prius. You need to look for cylinder wall scoring.

 

1/2 quart every 600 miles is a quart every 1200 miles which is considered excessive for this engine by Toyota. Under the powertrain warranty they were installing updated pistons, head gasket and rings for free.

If it were my car I would install a rebuilt or JDM engine considering the miles, oil consumption and blown head gasket.

A head gasket repair alone could be at risk of a repeat failure in the next year or two. It usually costs well over $2k and sometimes as much as $4500 depending on the shop.

In any case, try to find a shop experienced with gen3 Prius head gasket problems. One further test might measure the height of each piston at TDC. A short piston would force a rebuild or replacement.

Toyota oil consumption metrics and repair procedure which includes pistons, rings and head gasket.