Cylinder Misfires

Which is absurd; the Prius engine is just an engine. Any mechanic who would make a statement like that, about not working on "hybrid engines", you're well shut of them anyway. It's really just a brush-off. I would shake the mechanic tree a little more, who knows, but if no one seems competent/willing.

I'd second @Leadfoot J. McCoalroller, cleaning the EGR now won't roll back the clock on the head gasket, that's got to be first. The easiest, and quite conclusive, test would be boroscope inspection with coolant system pressurized. This link starts a Car Care Nut video fast-forwarded to roughly where he commences a boroscope inspection. Not sure if he mentions pressurizing the coolant system, maybe earlier in the video:

I don't subscribe to his EGR "remedies" BTW, which as an ex dealership mechanic, is purely replacement of parts.

Regarding the EGR:, you can DIY the EGR/intake manifold cleaning. It helps a lot to have a garage, basic mechanical tool collection. If you can manage an oil change or spark plug change, you can manage this. It's a little more daunting, but not too tough. Have a read through the first two links in my signature (if you're on a phone you need to turn it landscape to see signature).

The linked nutzaboutbolts videos are very useful, I really respect their skill level, takes me at least 3 times as long to do stuff they breeze through. Plus they were doing the job first time around, so I've comment on a few things they do, mostly in the second link in my signature IIRC.

Anyway, last fall I did the EGR cleaning on ours a second time, and it took me roughly a day, on-and-off. Started after breakfast, worked through the day, got everything resolved and more or less together, then spent the next morning wrapping up.

FWIW, I dropped in on a local Priuschatter doing an EGR cleaning: a 19 year old, in his parent's drivway, on a sunny winter morning, temp definitely below freezing. There's no way I could manage that. He got in touch with me a few days later, had it all back together.

 

If you’re not using coolant it’s not a head gasket. At 100K it’s the EGR that needs to be cleaned. Dealer will not clean all parts, only replace the EGR. Without a mechanic who knows Prius, you may have to attempt it yourself. But any competent mechanic can do it. Maybe speak with a dealer mechanic about doing it as a side job.

 

see second link in my signature (on phone turn landscape to see signature).

Yeah 100k is early for HG, typically around 150k. Sounds good.

 

Yes. YouTuber The Car Care Nut recommends to pressurize cooling system before doing the inspection, to make any leakage mor apparent. Not sure of the easiest way to accomplish that. IIRC there’s a little spigot on the reservoir neck, with a cap? Connect some sort of air pump to that?

around 10:30 in po:

 

Any real repair shop can do the Headgasket. It has nothing to do with the hybrid system.
I did mine... but never purchase a Gen 3...

 

"Real" is the operative word. You're well shut of the places giving you the brush-off; they're glorified oil-change places. Hopefully there are a few competent mechanics that can help, besides the dealership. There's a couple of links in my signature with head gasket related Repair Manual excerpts, might help if you find an independent mechanic who'll take it on.

 

Midas for a Head Gasket............. no....................

Have mechanic look at the HG replacement video.....

 

Watch level closely put a piece of tape where the fluid is...................

 

If your going to keep it also change trani fluid..... it's very easy............... but so many other things will go out........
brakes and traction battery............ has the inverter blown yet...............? But you are covered with that but happens and you are stranded....

 

Might want to think about selling it............ and if the HG is not blown change the trani fluid..... very easy
But if I were you I'd hope for the best and expect the worse....
When my HG went out.... it shook.. and had white smoke.... engine misfire code.... I changed the HG the next day... actually it took me all weekend. I hope for you sake it's not the HG.... but I would sell it before 150,000 miles..............unless you like financial and mental pain.

 

Denial
Anger
Bargaining
Depression
Acceptance

Just don't waste too much money in the first stage

 

See top two links in my signature for EGR cleaning tips (on a phone turn it landscape to see signature), soaking solution and such.

It’s good to clean the EGR for sure, but it doesn’t turn back the clock if the head gasket has started to leak.

With the wipers and cowl off, it’s a good time to do boroscope inspection too. Pressurize the coolant system (connect at spigot on reservoir neck maybe, never done it), then run the boroscope into combustion chambers. If any piston top looks oddly cleaner than the rest, that’s a sign; coolant steam-cleans. Also with cooling system pressurized you’re looking for coolant tears appearing at the head gasket seam.

 

Your miles are just into the yellow zone for head gasket failure. Red zone commenced around 150k. The head gasket fails gradually I think.

Don’t neglect the small EGR passages on the intake manifold, one per port. They’re the final leg of EGR passages, tend to clog progressively, commencing at cylinder one end.

I’m of the opinion the head gasket failures are directly attributable to protracted neglect of carbon in the EGR system. There’s some here who think I’m barking up the wrong tree.