2010 Prius with coolant and spark plug issue

welcome!
unfortunately, you unknowingly purchased a car model with a known head gasket issue that has been discussed here ad nauseum for many years.
the problem stems from improperly designed piston rings which allow too much combustion byproducts pass into an improperly designed egr valve (exhaust gas recirculation)

if the egr valve and intake manifold aren't cleaned regularly (and toyota doesn't recommend doing this in their maintenance schedule so no one knows but us) the pressure build up blows a hole in an improperly designed head gasket, allowing coolant to escape into your exhaust.
the low coolant allows the engine to overheat, damaging the entire engine.

you are right about your mechanic, she (and most, even dealers) doesn't understand what the shaking means.
changing the spark plugs smooths things out for awhile, until they get clogged again by the combustion blow by.
at this point, your best bet is probably another car, and you can weigh that against the cost of a used motor installation, but there are a couple of other very expensive systems on the 2010-2015 prius which might be a concern down the road.
if you don't diy, my advice would be to stay away from hybrids, and look for something like a corolla or similar decent mileage vehicle.
all the best!

 

yes, if the rest of the engine checks out as undamaged, a new headgasket will work.

idk how to be sure there is no other damage, so you want to do some research.

watch

 

Dump stop leak in the crankcase and resell it. Don’t let the moral police here pull ya over but many have done it.

 

This is like selling your soul to the devil. You will find someone who can DIY and give them full disclosure and you will lose far less than $12k. And still have your soul.

 

P0301 is a fairly specific code. P03xx indicates misfire, P0300 means general, non-specific misfire, and P0301 through P0304 mean misfire at cylinder one through cylinder four respectively.

Gen 3, model year 2010 through 2015, without fail, will blow head gaskets, anywhere after 100k miles, almost always at cylinder one, or two (the failure occurs at the adjoining wall between those two cylinders).

Symptoms include code P0301/02, rattle/shake at start up, and coolant loss. All of this is due to incompressible coolant leaking past the head gasket and accumulating in a cylinder, typically overnight, making the first cold-start in the morning most prone to symptoms.

Neglected long enough, you’ll get breakage in the damper between engine and transaxle, bent piston arms, broken pistons, and/or a hole in the engine block.

My “hunch” is the main culprit for these head gasket failures is the gross carbon clogging that inevitably occurs with the Exhaust Gas Recirculation system, newly minted and employed with 3rd gen, and very evidently now, not sufficiently tested by Toyota.

I believe periodic cleaning of the carbon in the EGR system will prevent the head gasket failure, and that is what I’m doing with our 2010, time will tell. For more info on that see the first two links in my signature (on a phone turn it landscape to see signature).

Your car is showing all the symptoms of typical 3rd gen head gasket failure, and if you decide to keep it, it’s imperative to address that first. There’s links on that in my signature as well.

Do clean the EGR in conjunction with head gasket repair, including the EGR passages in the intake manifold. This can be a DIY job, for next to nothing. The only component that “may” need replacement is the EGR valve, which has a relatively fragile internal mechanism, prone to wear. That component is a bit over $200 USD. You should probably replace the pliable gaskets at intake manifold too, around $30.

Head gasket failure at 133k kms is unusually early, possibly not too advanced. Boroscope inspection of the cylinders (for evidence of coolant leaks) and/or leak-down test (pressurizes the cylinders and checks how well pressure is held, and where leaks occur), are the go-to tests for diagnosis.

just curious: you ID the car as a “5”. It’s Canadian spec car? What size are the wheels; they’re OEM? Does it have the headlight washers and fog lights? That would be “Touring”, what we have. If it had 15” rims and dynamic cruise control, I believe that’s called “Technology”.

attached shows what touring looks like.

 

Grit, you’re losing it; it’s dump stop-leak in the coolant reservoir.

seriously, grit is being humorous, I think…

don’t use stop-leak products for a head gasket issue, they’re a short term, bandage solution, make an expensive mess of everything the coolant passes through. They’re the go-to chemical for unscrupulous sellers; should be bloody illegal.

 

We could know how true that "without fail" part is if we had another site just like PriusChat but where everybody with a Prius signs in and posts when their head gasket hasn't blown.

 

if you haven’t checked it out:

Gasket Masters video too:

 

Thought your dad and husband was the plan?

 

Certainly the head gasket is bad. Once you have the head off, you can look at the cylinder walls.
Are you burning oil? If so, the walls will be scored unevenly. If the oil burning is not bad, you will
probably be okay. Then you can start saving for a short block. Toyota sells them for an average
of $2000. But you can do some searching and find remanufactured engines for about the same
price, or slightly more. Same with a short block, but for less than Toyota's price.

Make sure you get the FULL engine gasket kit. It will have the gaskets and "O" rings for the
water pump, thermostadt housing, and a few others I can't remember.....

 

Here's the whole engine section, simplest way to skin the cat (terrible expression...).

 

Even here on the west coast the suspension on ours, particularly the rear, was rusting up in 4~5 years, when I started paying attention.

I did a couple of sessions, one for the rear and one for the front, put it up on safety stands, removed some plastic pieces for access, brushed off all the loose rust/grit and coated with boiled linseed oil, applied mostly with brush, some hard to reach with rags.

revisited a couple of years later, and it’s still holding up good.

 

Sorry you had to find out the hard way about these engines, particularly after bring lied to about the symptoms when you bought it.

A year later the mechanic admits

Many mechanics and forum “experts” are confused about gen3 head gasket symptoms because they don’t present in the traditional way.

No coolant in the oil. No obvious loss of coolant. Passes a leakdown and gas in the coolant test. Occasional misfire codes usually lead to the plug, coil and injector parts cannon. Often $1000-$1500 of wasted parts including a water pump in your case.

Too often, damaging sealer gets thrown in to temporarily mask the issue. Forum guys claim months or a year of success without mentioning they keep dumping in more gunk. Hopefully your seller was not one of those scumbags.

At an advanced state the rattles are no longer occasional. The “Prestone” antifreeze top offs become more frequent. The piston rods may slightly bend and the aluminum engine sometimes warps.

The oil rings were flawed from the factory and acknowledged by Toyota. The head gasket itself was revised. But the typical old gen3 engine will be massively carboned up and have a liquid sludge in the intake.

So the same mechanic who did not “know” about the failed head gasket somehow now knows the only guaranteed fix a year later is a rebuilt engine (probably not yours) with new pistons, rings, rebuilt head and all the gaskets. Dealers, pro mechanics and your shop know they can’t guarantee a simple head gasket swap.

Be very careful with the timing chain alignment. Many return to do timing several times.

A junkyard low mile engine fully rebuilt is the guaranteed fix.

 

Maybe “flawed” is a misnomer? AFAIK the rings met the design specs put out by Toyota, which included a markedly low outward springiness. Their motivation likely being to reduce friction, and consequently increase mpg. 2015 model year engines (and some 2014’s) have revised piston rings, with increased springiness. If you look at Fuelly year-by-year stats for 3rd gen, there’s a 0.3~0.4 mpg drop in 2015, vs the earlier years.

Toyota Prius MPG - Actual MPG from 8,884 Toyota Prius owners

3rd gen Prius (model year 2010-2015) also have a newly minted EGR system (Exhaust Gas Recirculation), which allows the engine to run leaner, again for mpg gain. As long as it’s functional.

We turned out to be the Guinea Pigs, with an EGR system which very reliably clogs with carbon, somewhere around 100~150k likes, and does so asymmetrically, with the final EGR passage to cylinder one being first to completely bung up.

It’s the common wall between cylinders one and two where the head gasket usually fails.