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

... and it is designed to do so.

Here is an alternative view.

 

We can only go off of the data that is available. I am an engineer and I often say I am from Missouri : Show Me.

I can tell you this: look at Craigslist and the mobile mechanics. They’ll do a head gasket for $500 in your driveway.

Think these ads would be there if this wasn’t an issue?

It can be many things: water pump failure, head bolt torque, gasket seating issue, etc.

All of those things we’ve seen here. And that’s the hard data available.

 

And the near complete carbon clogging: that was in the plan?

 

I clicked on Williams's linked video: recall watching it before, so just scrolled down throught the comments, which were mostly negative.

 

No matter what it was designed to do, engineers are not gods (I know because I am one) and the design must adhere to the physical laws.
Facts:

1. EGR causes a localized rich mixture which generates soot.
2. Soot accumulation in the EGR system prevents the purpose of the EGR system which is to greatly lower combustion chamber temperatures for mitigation of NOx gas generation. The side effect of lowering temperatures also lowers pressure. Failing EGR system = increased headgasket stress.
   
3. Soot accumulation in the combustion chamber increases compression = headgasket stress.
4. With lower combustion temperatures and pressures Toyota engineers probably had reduced the thicknesses of the components in order to reduce cost. This is very common in design. So we're left with an engine that can tolerate less extra heat/pressure before failing components when the EGR system clogs up.

 

Wouldn't a thicker gasket result in a more complex -- and probably less-desirable -- combustion-chamber shape?

 

Not a thicker gasket, a wider gasket

 

Unless we have data, we can only speculate on causes. The fact that a craigslist ad lists a Prius is not data. Nor are anecdotes -- how many cars failed in the same manner under very similar conditions? That is data.

We don't even know the rate of failure, and keep in mind that individuals with the problem are more likely to post in a forum as opposed to those who don't have the problem. If you search PC for "head gasket" you get 124 posts. That's not a lot, with 160,000 members and over 2.5 million posts.

• Has anyone who installed the catch can had a head gasket failure?
• What is the rate of plugged egr systems in head gasket failure?
• What is the rate of head gasket failures in non-plugged egr systems?
• How do you know that the addition of a catch can actually improves performance and reduces failure?

With respect to catch cans, contrast the following discussion with the catch can theory. 2010-2012 Head Gasket failure analysis | PriusChat

 

I would say that “mobile mechanics” finding enough work to travel to you is a good point of data.

How did they figure out this was a problem if they didn’t have data to support their new found employment ?

And their isn’t just one of them.

You speak about the need for data and how some good correlations can be achieved. The problem is not everyone participates and is willing to experiment in the name of science.

So those of us that are willing (and also help others) try to collect and share.

I also plan on installing a catch can on our Prime, but life has gotten in the way of this attempt at data .

Soon enough though .

 

In my opinion, unless you have engineering data, your risk of damaging your Prime far exceed the chance of providing an improvement. It is inconceivable to me to expect that such a modification would be beneficial. You have to get it right. There are literally infinite ways to get it wrong.

Mobile mechanics shotgun ads to all makes and models. The presence of ads means nothing on the internet. Would I trust a mobile mechanic to do an in-driveway head gasket on my hybrid? No. However, I might do it myself.

What about the alternate theory of coolant/gasket material? Please comment. And provide your design for a better head gasket in the spirit of the catch can.

 

Damaging our Prime, eh? You do realize the oil catch can isn’t a new idea and one that is actually designed into some cars.

The oil catch can is spliced into the PCV return, and when done with vacuum rated hose, it works well.

It’s a wide spot in the line and functions as a knock out pot to collect any liquid. Since the gen4 engine isn’t much different than the Gen3 (take a look at the swapping threads as some have transplanted a Gen4 engine into a Gen3), I’ll take my chances and provide data for others to benefit.

Why do I have to redesign something toyota engineered and most are getting 200k miles out of? If the “useable life” is thought of as 180 k miles, didn’t toyota do a good job.

I got the useable life out of our 2010 and then some.

 

HOW does it damage the engine?
HOW does the engine know how long of a hose you use? It just knows to suck in air whether the
hose is 4 inches or 4 feet.
How does it know if there is a "can" full of air, that the engine sucks in? Most of the oil will get caught
in the wire mesh in the can.
The engine seems to only know it's sucking in air.
At least that is what it seems to me.

 

Good luck.

 

Wow, you're helpful.

Pixel XL ?

 

We're all going to hell.

 

Good luck with what?

 

Not Me!

 

You sure ?

Maybe some of us are already there .

 

"Hey mama, look at me
I'm on my way to the promised land, whoo!"

My headgasket just failed...

Pixel XL ?

 

I'd like to return this discussion back to considering chief causes of head gasket failure on Gen 3 engines. Could a root cause be the combination of lower weight (0-20W) oil + extended oil change intervals that were introduced with Gen 3? Theory would be the lighter weight oil doesn't have the wear additives that higher weight oils contain, and combined with extended service intervals, the lighter weight oil breaks down and leads to greater oil volatility and increased engine wear at higher odometer mileages. Increased oil volatility and engine wear cascades into greater EGR deposits, higher combustion temps, leading to ... you know the rest.

Since i'm a newbie, i can't post reference links yet but if you google machine+lubrication+Motor+Oils+Fuel+Economy+vs+Wear, the first hit is a great reference article that questions the current trend toward lightweight synthetic oils for greater fuel economy/CAFE standards. One explanation for why everyone isn't experiencing this problem could be that many have simply not hit the magic mileage number where oil consumption and EGR deposits enter a deadly feedback loop.

Preventative measures to address this "theory": substitute a slightly higher weight oil (5-30W), shorten oil change intervals (5-7K miles), and install a OCC at the first sign of oil use.