What is the chief cause of head gasket failure on the gen 3

Some have theorized the issue is PCV valve placement resolved by an oil catch can. Some others wonder whether EGR design plays a role noting that Gen 4 EGR has been redesigned.
A regularly emptied oil catch can appears to be the best user solution at this time.

 

If the oil breaks down, bearings fail. And I would think that would happen first...

 

I agree - except i don't believe that bearing failure is a problem. Toyota has redesigned the piston and rings, so it appears that rings failing to seal is the problem, and that seems to happen in high mileage engines. Once an engine starts burning oil, there's more blow-by and that means more vaporized oil gets past the PVC, coating the intake manifold, and fouling the EGR.

So an oil catch should reduce the EGR soot/residue once the engine starts burning/using oil, but the question is how to prevent the ring wear and carbon build up that leads to the oil burning problem in higher mileage engines. Brand new Gen 3 cars don't use or burn significant quantities of oil right out of the blocks, so an OCC isn't initially needed. And that's where the argument that using a slightly higher weight oil and a more frequent oil change interval comes in, assuming it can prevent engine wear and carbon build up.

 

0W-30 is too thin as well, using 0W-40
Is best, and no change in mileage. CC is good idea as well as 5,000 mile oil changes.

 

From the looks of cyc1 and cyc2 leaks is the most common failure it’s thought the design of the gasket/motor is to blame. Regardless a 76hp prius should not be experiencing this. Damn Shame on Toyota, these auto industries cutting corners to save a few bucks and leaves the consumer on hefty repairs. Google head gasket failure Prius or ct200h it’s everywhere!!

 

Only those corner-cutting users that try to cut corners by driving beyond Toyota's designed lifespan of 100K miles

 

Yeah! Toyota claims the engine is good for 98 HP. 76 is what you get if you limit it to about 3900 rpm.

 

My intake manifold has always had a "lake" at the bottom, and the oil level on the dipstick never budges from the full mark. So far...

I'm around 84K kms now, and had a Moroso Oil Catch Can in since 70K. I check the OCC twice yearly, fall and spring in conjunction with biannual oil changes: fall there's about 50cc, spring about 80cc.

Just to verify, you're saying the head gasket tends to fail at cylinder 1 and 2 most often? That definitely seems to be the case. The EGR gasses feed in at the other end. Those gasses tend to cool the combustion chambers if I'm not mistaken. Maybe that efficacy falls off, going from cylinder 4 to 1, and cylinders 1 and 2 are most prone to elevated temps?

 

Preventing EGR cooler clogging: There's no way to do this running gasoline without changing the engine design of the Gen 3. EGR + low-pressure port fuel injection = gumming up the EGR system. Rich conditions generate the soot that clogs EGR. Both EGR gas and low-pressure injection contribute to locally rich areas inside of the combustion chamber. Burning oil also causes the local rich zones in CC.

EGR and port gasoline injection is not mixed very well and not homogenous enough to prevent soot from forming. However with a different engine design (direct injection, better mixing), or more volatile/lower carbon fuel (i.e. methane or hydrogen), improving the mixing of the incoming air and EGR gas streams - this will lessen soot and EGR clogging.

I think Toyota improved the combustion with Gen 4: the intake creates tumble in the CC that better homogenizes the EGR/gasoline/air mixture and Toyota added a precatalyst to reduce soot particles in the EGR. I understand that Gen 4 also increased the width of the EGR cooler which should also mitigate clogging.

The best we can do on gen 3 is to stay on top of it with regular engine maintenance: check your oil, EGR system cleaning to keep the combustion cylinder temperatures cool and balanced, PCV catch can, fuel system cleaners, and piston soaks to prevent/undo ring sticking.

 

why doesn’t the clogged EGR throw codes then?

 

Don't know for sure, but would guess that if the EGR valve stepper itself isn't stuck to some degree, then no P0401.

 

The EGR system tests itself during moments of deceleration: the ECU waggles the valve motor and watches for changes in the manifold absolute pressure resulting from EGR flow. That would seem like a fairly positive test.

 

I believe it does, from what I've read here, but way too late, when everything is hopelessly clogged, and has likely been so for many 10K's of miles.

 

Maybe hit or miss depending on the car and whatever variables there may be. Mine was clogged so much that soaking one end with brake cleaner still had nothing coming out of the other, yet no codes.

 

Yeah, plenty of life left in that EGR system...

The Toyota Warranty Enhancement mentions a code coming on (P0401), and/or shaking at start up. And says "the majority of vehicles will not experience this condition".

 

My experience with my 2010 was that the IM EGR passages were fully clogged at 97k miles. The car was "shuddering" at light throttle, gas-engine-on acceleration, speed mid-teens thru mid-20s or so mph. It wasn't full-on knocking yet, more felt like the road had a washboard pattern to the pavement. Cleaning the IM EGR passages remedied this, and my point being the car never had an EGR code even pending throughout the development of symptoms and the fix. I suppose it's possible the "ECU waggling the valve motor" test hadn't "caught on" yet, but the issue had developed over weeks before I dug in. Maybe Mendel is right in that it takes "many 10k's of miles of being hopelessly clogged" before coding, but I quite doubt that and GUESS that 2-trip detection, or at least thereabouts, should set the code once EGR flow is severely or completely restricted. My feeling is that the turd gen doesn't always set an EGR code even with complete clogging of the flow passages.

 

Grounds for a fraud lawsuit?

Fraud vs. Lying: What's the Legal Difference?

 

For reference, someone over at the Lexus forums reports a bad HG (confirmed through leak down test by Lexus dealer) on a 2014 CT200h at 75k. He said they had another 2014 w/ 100k in the shop that day also with a bad HG. So I guess the 2014+ with its updated internal parts aren't really all that much more immune?

 

As far as I know the engine revision was revised pistons and rings*. This was to mitigate oil consumption, doesn't eliminate the EGR clogging (might reduce it slightly, at most?), and a clogged EGR is suspected to cause raised combustion chamber temperatures, which in turn cause head gasket failure.

* My latest take on that, from what I've read here, is that both the pistons and rings were revised at the same time, likely partway through model year 2014 for Prius. The oil ring of the revise ring set is "taller": the new ring won't fit in the old piston groove. The old ring would probably fit in the new piston groove, but would be loose.

 

Driving it like a Camaro and using 0W-20 weight.