Engine Misfiring.

Probably head gasket has failed. Exhaust Gas Recirculation system and intake manifold ever cleaned? That’s the likely culprit; best addressed by 100k miles, at the latest.

 

If the engine coolant dropped, then its most likely the headgasket. I wouldnt drive it if its burning coolant because water does not compress and theres a chance youll bend your valves first since those are the weakest links to compress, as opposed to the coolant adding extra volume.

Look out to see if you are getting white steam coming out of the tailpipe, as thats a key indication of coolant burning.

Also you say its 1 and 3 misfiring, the firing order i believe is 1-3-4-2, so is it possible that if cylinder #1 has the coolant coming in messing up the spacing, #3 does not get its proper position to fire causing it too to misfire since it fires right after? Just a hypothesis, as i find it unlikely for coolant to seap in both if theyre seperated by #2. But your misfires are why your car is so sluggish since you are realistically only driving on 2 cylinders.

"Was never like this before and if I stop somewhere it doesn't do it again until it sits there for a day or so."

Thats most likely due to your engine heating up compressing your headgasket and less coolant seaps in. When you turn off the engine, the top and bottom blocks cool off which as you know, cold stuff contracts, therefore giving coolant a passage to get inside your cylinder causing your misfires at the start of the day.

Easiest and cheapest solution is to throw a bottle of coolant sealant. It works by solidifying the coolant when it comes near really high temperatures, which would be the edge of your pistons. Chrisfix did a good video explaining it if you are curious.

Best of luck

 

I wouldn’t do this.

 

Its not a permanent solution by any means, but itll go for another 10k miles before needing more again. I have tried it on mine, but my issue wasnt coolant coming in so it did nothing for me. The risk/reward ratio is worth it just to try and see if it fixes the problem. Because if it does, then you know what the problem was and you got it temporarily fixed. At the cost of $40, and slight chance your thermastat and coolant pump getting clogged. Mine never did, but i also didnt use the thick headgasket sealant. I also recommend picking it up from walmart if they have it in stock in the car isle, itll save you $20 because autozone, oreilys, etc. like to mark up the same exact bottle i noticed.

I think its worth a shot in my opinion

 

From other reports around here, the chance seems more than 'slight', and the thermostat and coolant pump seem not the only things to clog. So at the cost of $40, if it works, you know what the problem was before you made things worse, and now have to decide if fixing the head gasket plus the added head aches will still be worth it.

 

I suspect only people that had those problems post about them. But i hear you, and i too researched a lot into it before i committed to it. What are the other things that could be clogged? Because the only critical components im aware of the coolant going through the therma and pump, and while yes they can clog, i imagine they can also be unclogged if you were to take them out and clean them.

 

The radiator, the heater core, the EGR cooler, the exhaust heat recovery exchanger, and the throttle body deicing loop come to mind.

 

Head Gasket would be my guess.
You need to do a leak-down test to confirm a head gasket failure.

I'd stop driving it or you might be replacing the bottom end as well.

Search: Prius Death Rattle; Headgasket.

 

Sorry but typical shops and many here misdiagnose and recommend the shotgun / parts cannon approach followed by the kiss of death for the radiator and heater core, eg sealer.

You have already confirmed the hg when the mechanic saw moisture in the cylinders. You have spent enough on unnecessary parts and services to install a premium rebuilt engine that stops oil burning and the rattling.

 

Ah good points. I overlooked those since they are just straight passages. Perhaps the thicker solutions could clog the ports to the radiator, but the thin ones have the same viscosity as water and i dont see them being an issue personally.

 

If you are gonna go that route, you might as well look into a gen 4 engine instead of gen 3. They made slight tweaks to them that they dont have this headgasket issue that the gen 3 are notorious for. Because it is bound to happen again, its a design flaw because the engineers overlooked the application of the engines headgasket. I would still attempt to just pour a bottle of hg sealant first if you plan on swapping it out. You might find out your problem is fixed and youll save $1300 plus labor costs. Im cheap though, and this isnt the correct, proper, or "right" way to do it as other people will tell you. But this is the way i do it and it pays off for me.

 

Never ever, ever, never put any head gasket sealer in it.
Unless you just plan on scraping the whole car when the head gasket goes.
It will clog the whole coolant system. And it will just about be impossible to clear it all out.

 

If their labor rate is less than $130/hr then you're money ahead with exchanging a 190,000 motor repair @ 16 hrs of labor for a 45,000-65,000 mile motor replacement @ 6 hrs.
Just be aware that Head Gaskets are not a wear item, and if your EGR circuit/throttle body caused this failure, I'm thinking that it will not be alleviated with a new long block.
Read all warranties and guarantees carefully!!!

 

If you transplant a fourth gen engine in, but retain 3rd gen EGR and intake manifold, I would periodically clean the EGR and intake. My hunch is those are the notorious items.

Going to 4th gen EGR and intake manifold is a can of worms best avoided.

 

I hear 4th gen EGR is slightly wider in its passages to prevent build up from occuring inside. Same with the egr holes in the air intake. Another thing is the fuel line position is moved upwards on a 4th gen engine, and the bolt placement is different for the egr. Not big problems but some things to keep in mind when trying to swap.

Why would you not want egr and intake replaced as well? Aside from the additional cost incase they dont come with the engine

 

Not sure, because it’s possible? But they don’t play well with 3rd gen’s computers apparently. FWIW, EGR in 4th gen draws gas downstream of cat, third gen is upstream. And 4th gen EGR appears to be near-double in cross section area. I’m periodically cleaning ours, will see how that goes.

My moneys not so much on “slight tweaks”, more on the 3rd gen’s EGR design.