Cause of Gen 3 Prius Head Gasket Failures

No EGR system on the Gen 2 certainly is a big part of the answer.

 

The gen 2 does have a basic EGR system, it doesn’t have an EGR cooler like the gen 3

 

I noticed that, had the same thoughts. Put a comment about the EGR clogging (a day or so back), and how it likely raises temps, maybe beyond what the engineers designed for.

 

I see that now. I guess designing a cooler that functions as a filter might be more properly part of the problem.

 

Gasket Masters observes that the 2ZR engines in Corollas with the same HG [exact same part number in fact] don't have failures, while the Prius and CT200 do. They posit that the hybrid operation causes more stress on the HG because it heats up and cools down multiple times for the same trip that a Corolla would only heat up once. Stress fatigue then causes the HG to lose its ability to expand enough to contain the gap. So in their view the use of that HG on a hybrid is a mis-application. (I hope that's a fair summary of their explanation.)

I have to respect their wrenching experience and am grateful for their Prius HG replacement video. Not sure I buy that theory yet though.

 

Could be a combo of the two. I wonder too, if some newer Corollas had similar EGR components as Prius? Not sure. Googling a bit, I think they only have a rudimentary EGR, not cooled.

 

Well I'm just waaaay out of my depth when it comes to head gasket design parameters, so I'll gladly give them their due. But we know that our 3rd gen EGR setup leads to uneven distribution of EGR gas due to clogging of the IM. Comparisons of equivalents are helpful -- if any Corolla has similar EGR it would be useful data. Also in Gen4 we know they increased EGR volume (wider pipe), increased EGR velocity (less bendy piping), and improved even per-cylinder distribution of EGR (modified the ganging of the EGR passage inside IM) [all this from that memory of that Gen4 teardown article you posted Mendel]. But did they also modify the HG design in any obvious ways?

 

Yes and No. I'm an Uber driver and head gasket blew at 236k miles.

Thing is I'm in a unique area where I do 90% highway miles which means engine is running for full 45 miles before shutoff.

So yes what he said about why the gasket go is correct but it's not prematurely broken by alot of stop and go.

Posted via the PriusChat mobile app.

 

Gen 3 was the first Prius to have any form of EGR, but you might have seen some posts that described the engine's Atkinson-cycle-via-valve-timing design as some kind of EGR. I've seen those posts too, but they're under a confusion. The Atkinson-ish valve timing works by closing the intake valves late, not by opening them early. Stuff does get pushed back into the intake manifold that way, but it isn't exhaust, it's fresh unburned fuel charge.

 

100% agree. And that's the reason prius don't come with a temperature gauge, mechanics will tell you that your thermostat needs to be replace, your temps are fluctuating up and down consistently

 

So, more duty cycles for the head gasket. Easy to appreciate.

And likely also these cycles become more extreme as the EGR system clogs due to less inert intake gas. And also as the EGR system clogs, resulting in less flow, there becomes an increasingly uneven temperature distribution across the cylinders, causing even more gasket stress. I'm thinking that as flow into the EGR gallery of the intake decreases, a greater portion of the flow gets sucked into the (closest) cylinder #4. Eventually there is little EGR flow reaching cylinder 1, and that cylinder runs hottest, hence common failure there.

There was an intake manifold redesign. Anyone know how EGR flow was redistributed?

 

I don't think I buy the engine-off theory: the engine hiatus is mere seconds. I don't see engine temps yoyoing in such a short interval. I did have scan gauge connected for several years, usually with engine coolant temp displayed, and I saw no wide fluctuations.

The intake manifold revision, which Toyota seems to have lost interest in, was I think a passageway revision, from four-into-one, to four-into-two-into-one. Mostly conjecture, based on a 4th Gen cross section pic I saw.

 

Measuring Cylinder Head Temperature directly would probably yield the necessary data to at least make a guess on how widely the temperature does vary in the head itself. Crossing over to aviation, for example, our fleet comes with digital CHT gauges as our application does involve problems with thermal cycling. Too high of a cooling rate and the cylinder itself cracks so I can get behind some of this theory but I’d love to be able to document the data in the Prius to see just what’s happening and how much variation is occurring. If one was able to measure these temps, perhaps it would be possible to see a trend over time of one or more cylinders starting to run hot as the EGR system fouls...


iPad ?

 

Engine does not cool that fast especially without a thermostat.

I don't think a non-functional EGR via clogged system would affect anything.

I say it's the material of the head gasket. It was chosen for some reason and tested out and appropriate warranty was issued to avoid major costs in replaceing a mass of head gaskets. When I was rebuilding automotive they didn't have these Multi-Layer Steel head gaskets. So tech would have been on the new side in these cars.

Posted via the PriusChat mobile app.

 

Did I miss something in this thread about removing the thermostat?

 

I found no thermostat in my 2zr engine when I had it apart

Posted via the PriusChat mobile app.

 

Is it possible you just overlooked that it's integral with the water pump inlet, or had someone been in there before and actually somehow pried the thermostat out of the inlet, or replaced the inlet with some aftermarket one that somehow didn't include the stat?

 

I didn't include the word "wide" with fluctuations. I am getting poo pooed rapidly on here as of recently, russian collusion does exist!!! On another thread, I replied with turn on the solar roof fan, someone replied & said there's no 12v fan in the car to expel air out.

 

We don't really know why head gasket fails. So we add ideas, observations. Is collaborative. Poo-pooing? Nyet.

 

Answer the question!! I think you are totally wrong, because this is not an issue with the Gen 2! Why is this so-called problem not an issue with the gen 2?!

 

I did a search for "head gasket" in the Gen 2 Prius Care... forum, and got 185 hits, so is this really a non-issue with the Gen 2? How similar is the head gasket in the Gen 2 to the Gen 3? The statement in the video stating that the head gasket failure rate in the Corolla is much less than in the Gen 3 Prius, both having the same engines, seems like pretty logical reasoning that thermal cycling is probably the cause of the more frequent head gasket failure in the Gen 3.

 

From looking at "The Car Care Nut's" video on YouTube, I'm led to suspect that the condition of the coolant has something to do with head gasket failure. Maybe more frequent coolant changes are in order.