2012 engine shake on start, no codes

It may be good to do the timing chain if you're keeping it a long time. I've not read any reports of timing chain failures on the Prius - you may want to do a search and also start a separate thread. Though, I would definitely replace the oil pump & water pump.

No intervals for timing chain or head gasket replacement that I know of. These are not within the normal service life of the Prius for most people so Toyota doesn't specify.

If you have time, the EGR and EGR cooler can be cleaned at home using common tools and chemicals. There are threads on PC that describe this.

Also check out the Toyota Owner's website - it may provide some information about your car's service:
Toyota Owners Official Web Site

 

Regarding timing chain viability: with @danlatu 's complete (DIY) disassemble of a 2010, with 297K miles, I don't believe he replaced the timing chain, and he had the engine out and disassembled. I would defer to his judgement. Eye opening read:

Blown Head gasket rebuild....@297k | PriusChat

 

I'm sorry for your luck. I do appreciate your tenacity. Hopefully you still got a good deal or can contact the seller.

There are many possible failure modes and your engine failure could be caused by any combination of them. A lot of these are common to other engine designs. The following are some common ones that are discussed on PC.

These engines are tuned to run a lean mixture diluted with cooled exhaust gas (EGR). The EGR cools down the combustion chamber. When the EGR cooler plugs there won't be a fault code because there's no sensor measuring EGR flow. So what you get is a steadily hotter combustion chamber where the engine injects more fuel (O2 sensor) because now it's drawing more air and less EGR.

In @danlatu's "Blown Head gasket rebuild....@297k" thread we learn that the Prius engine comes equipped with oil squirters that cool the pistons and cylinders. These help cool the pistons and combustion chambers. Dan noticed that these were clogged when he did his rebuild. If you do a google search on "oil squirters" there are reports that clogged oil squirters lead to an overheated engine. When the oil squirters clog there's no resulting fault code. Would this lead to pistons expanding from the heat and cracking the block?

Was this engine an oil burner? Low oil can overheat the engine. Also reports of a clogged oil control ring scraping the oil off the cylinder causing a drier cylinder leading to more friction = engine overheat. If the engine burns lots of oil there's no fault code.

An overheated combustion chamber can cause knock. This probably lead to your block cracking.

The theme is there are lots of ways an engine can self destruct without triggering a fault code. Proactive maintenance can prevent these from happening.

 

I was reading a bit more about the 2zr-fxe Prius engine 2ZR-FXE Toyota engine. It has iron cylinder liners inside an aluminum block. If they could be replaced I wonder if, after disassembly, the crack can be repaired easily? Anyway, its above my pay grade.

To the OP - best of luck to you! I'd be interested in hearing how this turns out.

VS985 4G ?

 

The EGR cooler is basically a pipe with an internal (engine coolant fed) radiator, the first in light of conduits shunting exhaust gasses back to the intake manifold and into the combustion chamber. Could it's radiator fail, leaking coolant, and would coolant then make it into the combustion chamber? Not sure, and it's a long shot.

 

Mendel, I would think if the leak was in that little EGR radiator, that the coolant would be fairly evenly distributed across cylinders. OP reported that 1 spark plug was darker than the rest, suggesting to me that the problem was localized near that cylinder. My ancient experience with other car engines was that the color of the deposits on the cylinder consuming coolant was a different color than the light tan of the normal combustion cylinders.
Anyway, good luck to OP in resuscitating or replacing this engine!

 

It will be completely fine, my father and I just swapped a 2010 engine with a blown head gasket for a 2012 Prius-Plug in engine with 40k miles. It works perfectly, no engine lights or anything!

 

Lucky You! May you have many trouble-free miles!
(But hopefully you checked HOW the donor car for your engine was totaled? Best is hail or tree fell on it, second-best is rear-ended, third best is T-boned from the side, worst is front-ended as the engine/eCVT unit is submarined if the front crush comes in far enough.)