Death rattle?

Low coolant and cold start severe rattle occasionally equals leaking headgasket. A competent mechanic with a quality borescope can confirm or you can just wait, it will get worse. Unscrupulous sellers will often use a temporary sealer.

Check with Hometown Hybrids for recommended shops. I prefer a rebuilt engine with Toyota's revised pistons and rings. Less than $5k installed.

 

A good borescope will often see a cleaner piston. In rare cases a superior borescope with a pressurized coolant system can see water drops at the head gasket. That requires a scope with multiple views. If it is losing coolant and has severe rattle, it is a very common head gasket.

Usually observation alone is conclusive:
Shudder video

Detail for those in denial:

I am afraid the head gasket issue is common in the 2010-14 1.8L Prius engines.

Many go through an emotional roller coaster and try many other quick fixes, wasting money. Disregard the advice to clean egrs, change coil packs, plugs, etc. The pattern of many 1.8L head gasket failures is in your post and has been reported fifty times in this forum.

Starts out with a very occasional rattle, sometimes weeks apart. No observable coolant loss or white smoke. Egr system is cleaned with much effort and the immediate results are good. A few days later the rattles return. Plugs, intakes and coils replaced with identical results. A few days grace each time only to be disappointed.

A coolant hydrocarbon check or leakdown test will be negative in the early stages. Most mechanics believe this common diagnostic is conclusive but it ends up being a false negative in a week or two. Later when its rattling every other day and coolant is down by an inch, the hydrocarbon test "might" be positive. A borescope test is usually definitive by then. At gen3 head gasket end stage with rattling at stop signs and white smoke observable in the rear while revving, all leakdown and hydrocarbon tests are positive. Rarely will there be coolant in the oil.

Initially hg leaks are slight, very occasional and don't present like traditional head gasket failures. Sometimes early teardowns don't have a physical break in the gasket but coolant leaks to the cylinder under the gasket. Apparently caused by minimal warping that is quickly sealed as the cylinder heats up. Uneven cylinder cooling design is a contributor. On occasion, a loosened head bolt achieves the same thing, typically after a poor repair. Worse case, "waiting" causes a rod to bend and eventually break. Holes in the block can result.

Overall this is a flawed design that often points to the 2010-14 piston ring flaws which then aggravates a poor egr design. All redesigned by gen4 with the gen3 rings improved by mid 2014. Gen4 also significantly redesigned cylinder coolant passages and added an insulator.

Get it fixed early.

 

If it's low on water it IS the HEAD GASKET....100%

 

If you get the head gasket replaced, immediately thereafter clean the EGR system (including intake manifold) thoroughly, or you’ll likely blow another head gasket, in another 10~20k miles.

my 2 cents: a 3rd gen that’s had EGR cleanings every 50k miles will not blow the head gasket.

I'm loath to quote these guys, but they do see a lot of 3rd gen head gasket failures. They say it's happening in all the years of 3rd gen, including the 2015's which for sure will have the revised pistons/rings:

https://www.gasketmasters.com/head-gasket-replacement#:~:text=The%20head%20gasket%20on%20the,Gen4%20(2016%20and%20newer).

 

Egr cleaned every 50,000, head gasket blown at 167,000. Oil changes and fluid maintenance per Toyota. Hot and fast conditions in Texas.

 

Dang, that took the wind outa my sails… intake manifold included in that cleaning?

 

Another Junk toy HG goes down..... what a crappy design.......... but someone on here will tell you what a great car they have cause they have 40,000 miles on theirs and no problems.

Then the brake sysetm...........traction battery

The only thing good about the cars is the mpg................ I'll never own another one.

 

^^^This^^^ But it's much less work to do the EGR at the same time.

It's pretty clear that the HG has failed. Gasketmasters makes one that's much better than the OEM gasket. There's another one with a good reputation, but I can't remember the name of it.

However, if you do the HG and ignore what seems commonly accepted as the most likely cause of its failure, the new one won't last long. To remove the head, the intake manifold and egr cooler need to come off anyway, so go ahead and clean them along with the EGR valve and pipe. And don't forget those little ports in the IM; they clog unevenly and I think they are the real source of the HG troubles.

 

Just curious, who was the seller? I'd think the odds are good they were ditching the car...

Tough call. If you can DIY head gasket it's less of an investment, time and expense. Otherwise trickier. One option in california is Hybrid Pit Stop; their gold package refurbed engines are just under $3K. They offer install, not sure how much.

The code for EGR clogging is P0401 IIRC. One issue: the intake manifold EGR passages clog unevenly. Typically cylinder one can be nigh totally crusted up with carbon, while the rest are better, and the car's computers see semi-decent flow overall. It's the wall between cylinders one and two where the head gasket failures typically occur.

Very frustrating. In reference to EGR clogging, Toyota says (in the Warranty Enhancement Program, dated May 2017):

"while the majority of vehicles will not experience this condition"

which is a flat-out lie; it happens to them all. They underline and italicize the statement too, just like the above.

 

And remember the next 2 problems....
Brake System $1500 or more
Traction Battery...... $1500 and up if done yourself.... and get a New one...not rebuilt used.....
And better change the water pump.
I did my own head gasket and it wasn't fun but I had 2 other vehicles to drive... I started on Saturday and finished on the next Saturday.

 

With a head gasket problem you won't get codes because the misfire does not last long enough. Which basically eliminates bad plugs, coils and injectors. This scenario virtually confirms a head gasket problem.

I would not count on a simple head gasket replacement giving you 100,000 more miles. Even with a thorough EGR and intake cleanup or replacement.

However, a quality rebuilt engine built by an engine shop has every possibility of making another 150,000. At a minimum you want a one year warranty either way.

 

This car could go another 100 + thousand if....

It doesn't use oil
Didn't get to hot
Change Water Pump
Change Trani Fluid
Rebuilt head.
But looming brakes and traction battery. $3000 or more.