Should I replace the engine?

- Had the same issues initially as The Critic (2011 Prius Head Gasket Failure | PriusChat), cylinder misfires on my gen 3 prius @ 205k miles with knocking and vibration.

- Replaced the ignition coils with cheap ones from amazon. Check engine light came back on.

- Replaced the ignition coils with Duralast ones. Check engine light still came back on

- Replaced the spark plugs. Check engine light came back on. Noticed temp light turning on.

- Took it to a mechanic for an cosmetic issue, he diagnosed the issue as Engine Coolant Temperature Sensor 1 Circuit Low (code P0117). Also recommended seafoam to be added to fuel to remove carbon build up?

- Replaced sensor (found the sensor location in this post: [Solved] Engine Coolant Temperature Sensor location? | PriusChat). Everything seemed to work just fine for 2 days. Check engine light came back on and so did the temp light.

- Noticed Coolant levels were dangerously low, foolishly purchased a Autozone branded one (because i'm cheap too ). Coolant levels dropped rather quickly same night, topped off and yet they dropped off rather quickly.

Now, I'm wondering if I should simply the engine coolant and replace with zerex asian cars red coolant. Should I replace the inverter coolant too? Do they mix? Or take it to firestone/jiffylube/mechanic for a coolant + radiator flush (This was recommended by O'Reilly tech (they don't provide flushing services though)?

At this point I'm $300-400 down and would like to fix it myself (simple stuff only. in case you haven't noticed, this is the 1st time I opened the hood of a car ). Or should I simply go for an engine replacement (Head gasket issue sounds like too much work for me and I'm still not sure what the root cause might be) ?

 

I tried locating the source, but couldn't find one. I did find wet spot on the ground right beneath the engine coolant box, when refilling with coolant the second time.

207k miles (Brought at 190k). Never cleaned the EGR components or intake manifold. Will look into it, see if I can perform them myself, if not I'll ask my mechanic if he can.

Update since posting the question: The mechanic is recommending Induction cleaning? To clear up the carbon build up near the pistons... Is that worth pursuing? He did recommend seafoam which I tried and the car ran much better for a while, alas, that didn't last.

 

@Mendel Leisk - Just clicked on your link and EGR and Oil can and realized both you and my mech might be talking about the same thing.

In case there were any doubts about my expertise under the hood, please refer to my username

 

Sorry in advance if my reply seems defensive:

I don't really care about the coolant, just read on the forum that OEM or Zerex asian cars one is recommended.

Right now the car is just sitting there in the parking lot while I wait for a mechanic to be available. Only topped up the coolant since it was pretty low the other day (stopped doing that after noticing leaks ).

As for throwing parts at it, replaced the coils and spark plugs as that was the code I got (P030x). Same with the coolant sensor (P0117, diagnosed by mechanic while getting work done on unrelated issue).

Honestly, hoping for the best (EGR cleaning) and preparing for the worst (engine replacement).

How would one go about finding these parts (except calling junkyards and searching on ebay)? Labor cost for replacement also seems to be pretty high unless I can find an experienced user in MO willing to work together on the car like @Rebound or @Raytheeagle.

 

I'm sure I'm grasping at straws here, but does anyone know what this white cap is right next to the engine coolant temperature sensor is? It's missing on my prius. (Pic provided by @Mendel Leisk in another thread)

 

In the process of following this video 1st to check for build up in EGR pipe. Looks simple enough for me. If I find some build up, there's some hope (i think?), and will proceed to other build up cleaning. If not I'll have the mech do the induction cleaning. He mentioned he has a machine for that and it's the likely cause for engine knocking/rattling.

I'll ask about the leak down and boroscope tests. Hopefully they don't cost too much.

 

Update: Got around to removing the EGR pipe and cleaned it a bit. Is this amount of carbon build up normal?

I need get off my butt and clean the intake and close it up.