Clunky sound when engine starts and more.

Start by making sure you’re up to date on all recommended Toyota maintenance.
Then clean the egr circuit.
Next, move on to things like throttle body cleaning, coils and injectors

 

That's the usual Prius headgasket/rattle issue. The fixes for it are not the same. Some folks fix it by cleaning the egr, intake manifold. Some folks fix it by replacing coils and sparkplug. Some folks fix it by installing catch-cans, replacing pcv valve, etc.

My advice, just give your Prius a full-blown TLC by doing all of the above. Replace all fluids as well like coolants and atf. Also, give it a bottle of fuel treatment and do this reset on this video.

 

How's the coolant level?

With the miles, and no mention of EGR cleaning, I'd test the head gasket integrity. A couple of things you can do (or have a mechanic do):

1. Leak Down Test, where cylinders are pressurized one at a time, at TDC of compression stroke, using a special gauge set. You're looking for abnormally fast pressure drop (with the gauges), and looking/listening for evidence of air escaping, and where it's escaping.

2. Boroscope inspection of the combustion chambers while the engine cooling system is pressurized, to look for coolant leaking into cylinders.

Think this is a direct link to your video:

2012 Prius Start-up - YouTube

^ hard to tell anything, audio very low

 

https://m.youtube.com/shorts/ZrvsPPlkgyQ

That particular rattle isn't that bad, however, if it was more severe before, perhaps 5 to 20 seconds with an almost metal to metal rattle and the engine shaking, that's a head gasket for sure.

If it is a head gasket, it will return. In the early stages it can take days or weeks between severe rattles.

All the maintenance listed above is good to do on a good engine. I would verify that your engine is good before you do it. With high miles, a replacement engine or better yet. a rebuilt engine is often the end result. Rings are usually bad as well making a professionally rebuilt engine the smart choice. No use putting in $1000 or more dollars on maintenance until you know for sure what you've got.

 

You can do far better than that in the Houston area. Start with Houston Hybrids and ask for recommendations.

Many can get a used engine installed for $3500 or less. Not the greatest solution unless you are ready to flip it.

Smart shopping and a good independent shop will get you a rebuilt engine with new pistons and rings installed for less than $5k. This is the smart move if you want to keep it. Think about those $900 car payments for four years and rebuilt sounds good.

A head gasket job is possible for $2k all in. Make sure you get a one year or better warranty as this is sketchy sometimes on a gen3.

There is nothing special about the engine. People have swapped them in less than a day. Hybridpit in Cali will ship you a rebuilt engine. Do your homework.

 

Hometown

 

This happens to many owners, at the freezing temperature of water, condensate freezes in the intake manifold, and the engine starts knocking at startup, I don’t think it’s worth worrying too much about this, Toyota has released a bunch of versions of the intake manifold, but the problem has not been solved.

 

It also can be the head gasket, which is why members will advise to check that. The dealership seems to have confirmed that in this case.

My old Gen 1 started making startup rattles like that at around 198,000 miles and I never figured out why. I doubt it was the head gasket because I drove without further for four more years until an incident involving an eastbound Dodge Dakota, and it still was driveable after that, and I sold it to someone who drove it to Colorado. It also wasn't the EGR system because Gen 1 didn't have that. Seems it can be a number of things.