No "how-to" head gasket posts for a Gen4?

These were 4th gen's?

Due to some symptoms?

 

Was the exhaust heat exchanger leaking? Maybe previous owner had neglected coolant top-up, let the engine run dry a time or two, led to head gasket failure. That’s been reported here before.

 

+1.
I was tapping this while he was typing that......

First, make sure you really have a failing head gasket!
The G4 has a common manufacturer defect in the exhaust heat exchanger that can cosplay as a blown head gasket.
Cracks in the plumbing allow coolant to leak directly into the exhaust system rather than onto the ground by causing mysterious coolant loss and white exhaust smoke without the Prius Death Rattle caused by coolant getting into the cylinder bore.
Toyota released a technical service bulletin (TSB T-SB-0135-19)and I suspect that there will be a video as the G4s age a little bit more and suffer from being "dealer maintained."
G4's probably overheat more from resulting coolant loss because you do NOT have the Prius Death Rattle, and this WILL cause head gaskets to fail from heads warping rather than blocks being hydro-locked.

The oldest G4s are coming up on 10 years and truthfully speaking they have been much more reliable than the G3s.

 

One thing, it’s early years of gen 4 that we’re having the exhaust heat recovery (EHR) system leaks. My memory’s flakey, but it might have been resolved by model year 2019. Not sure though.

 

Not sure he's saying that.

Sequence that does make sense, assuming the EHR system did have a leak:

1. EHR system commences leaking.
2. Owner doesn't notice for some time, belatedly tops up coolant, but by then engine's run dry a time or two, overheated, and head gasket commences to leak coolant into combustion chambers.
3. EHR system is bypassed, but head gasket continues to leak.

Regarding your original question, I think 4th gen head gasket replacement would be VERY similar to 3rd gen, the engine being "mostly" identical.

The imgur video sounds "somewhat" too noisy. Is it worse on cold starts? That tends to be when significant coolant accumulates, causing very nasty sounding bangs.

Just technical: is there an arched/ribbed face of the wheel chock against the ground, and flat face against the tire? If so, think it should be flipped:

 

And if you don't get hot coolant going pass your temperature sensor ( too low) your dummy lamp isn't going to light up....

You could've crushed some cooling coils, that isn't leaking, but caused enough restriction to reduce cooling capacity. Newer car designs are very stingy on parts requirements and there isn't much excess capacity to spare on folly.

PS: the lower radiator coils may be for ATF cooling - double check the manual. If that's the case; you may want to look at the condition of the ATF.

 

I'm curious why you bypassed the EHR system. I thought it was a known issue and was redesigned by '19.
I don't think that oil cap looks that bad. It's probably not after you did your big road trip. And on Gen3's the oil rarely gets into the oil. It just seeps into the #1 or 2 cylinders after shut down. This I know, a few times.....

Brother, I just found this thread and I'm following it. Good Luck. I'm sure you can handle this head gasket change.
Does Felpro offer a Gen4 version?


I bought a '19 Eco in Dec, '25 with 232k miles.
I think a courier had owned it. And I use it commercially also and I'm now at 280k miles!

It runs great, uses very little oil between 5-7k mi oil changes. Mobil 1 all the way!
I may do an oil analysis test on it because it looks cleanish.
What's with the 25k mile M1 version? I may be the perfect user for that crazy figure.

All I did to mine soon after I got home was change the transaxle fluid to Redline D6.
The ATF that came out was fine looking, so I'm pretty sure someone gave it a change at some point.
And I cleaned the battery pack fan filter, It seriously needed it.
I know I should change the engine and inverter coolants... It's a bigger job....

 

Sorry for your problem.
But to me, This is good news!!!

 

Think you’ve got it right: 3rd gen it was at top, 4th it’s at bottom.

 

Nope.
I said: "First, make sure you really have a failing head gasket!"
You've already dealt with the EHR either proactively or reactively.

It seems to me that there is one definitive way to determine if your head gasket is head gasketing, which would be to perform a leak-down test. It generally costs you nothing but time if you have a parts house that will lend you the kit.
The semi-conclusive test would be to bore-scope the bottom end and look for signs of 'steam cleaning' or coolant present in the bore.
This is also likely to be a no-cost test in the Commonwealth of Kentucky even though auto parts houses do not usually lend out bore-scopes
These instruments have non-automotive uses and it's almost certain that you or one of your friends or neighbors already has a scope in 'another' tool kit.
If all else fails - just get one on Amazon for about $30.

The REASON that there are not many head gasket threads for the G4 is that it's not a common failure for these cars.

 

Just a note: There are 2 kinds of 'leak down' tests.
The one you're referencing it a Coolant system pressurized leak down test. 15 PSI is the typical pressure used.

Another Leak Down test is used in Aviation and in the auto world is Combustion chamber leak down
The spark plug is removed and each cylinder has to be tested at its TDC and manually held in place.
A typical aviation pressure for this test is 80 PSI.
And with this test you'd then look for the coolant system to rise in pressure.
Which means you need two test sets and two pressure gauges in action at the same time.

With pressurizing the coolant to 15psi pushing thru a < pinhole in the head gasket takes time to visually see it happening with a borescope.

Good luck C Clay. Post pics of what you find!!

 

+1

 

Not good. But was there the 'Death Rattle' when you first started the engine, like reported with Gen3's?
If all that coolant came from one cylinder due to a pinhole in the head gasket there would be some misfire and noise, I would think.....
And the coolant would clear quickly. I have experienced this...

This seems like something else.
This seems like a pool of coolant is getting heated slowly and removed from the exhaust system.

Are you sure all coolant hoses are removed from the EHR parts near the CAT?
Is it possible the EGR cooler has a coolant leak?

It's time to go borrow the coolant system pressure tester from your friendly auto parts store.
Leave the coolant pressurized for 30 minutes to see if you can see the level drop in the reservoir.
And then start the engine, and I'll bet it starts fine but starts making this steam cloud again.

Good Luck !