2010 Prius 194k miles

Check the 12v battery. In the trunk, passenger side. You'll have to pull the carpet and tray out
to get to it. If it's under 12 volts, it might be bad. Look for a date code.
How long had the car sat before you got it?

 

How long is every once and a while?

You might want to look at the 12v.

These cars click, clack and knock for various reasons, they will tell you its the head gasket or HV battery right away.

First things first have the 12v checked.
Then replace it if needed, the HV battery starts the engine so if that is weak already and you start the car "every once in a while" then that HV may need attention.

Make sure you have a fresh oil change and check the dipstick in the morning before starting the car.

Depending on your DIY skills and pockets
I would change the air filter and spark plugs to start, then you will hear people on here clean the EGR cooler!!!!!

You need to drive these cars or else the batteries drain just sitting there.

http://www.RedBullet.net

http://www.ProjectLithium.com/?ref=mG0GE

http://www.Pulstar.com

http://www.PlugOutPower.com

 

Yeah. 194k miles, no kidding; it’s overdue. More info:

Bad Flywheel | PriusChat

Oh, and: if you ask about this at a dealership they’ll look at you like you’re speaking a foreign language. And/or do a parts replacement frenzy that’ll set you back close to a grand. Everything IS cleanable, but dealerships don’t do that. DIY the cost is trivial, under $100 even if you replace every gasket you encounter.

 

yeah, the egr circuit cleaning is like the 2nd to last big boss of videos games. Then save a few more grand for the final big boss- engine head gasket replacement. But you’ll need to pass level 1 first.

 

Except, if you defeat that second-to-last boss (EGR and Intake Manifold clean out), early enough, maybe the last boss (head gasket failure), never shows. Again though, 194k is late in the day; 100k is when you should get on it for sure.

 

how absent-minded of me, forgot the game of wack-o-mole. This car comes with 2 games!!!

 

Install an oil catch can early enough and we'll see if we can have the final boss lay in the background too.

So far with the catch can install on our 2019 Prime I've caught over 5 ounces for the 20k miles it has been installed.

And that's at 67% EV for those miles.

I'll see how much the catch can and egr circuit redesign help ward of the final boss.

Note on the Gen4 / Prime that the second boss got harder.

But I'm up to the challenge for some data.