What causes headgaskets to blow?

I feel like the fact that the head gaskets are just plain crappy quality is not mentioned enough. It's the coating that always fails. I doubt the gen 3 would have had nearly as many failures if they had just done multi layer steel originally.

 

I thought the new Toyota head gasket revision did away with the coating?

 

Exactly, don't those fail way less? When did the revision start coming on new cars? I mean, are there (m)any Gen 3 owners who's HG failure hasn't been the coating between 1 and 2 wearing away?

 

As far as I understand, the reason has not been found why the head gasket begins to leak on gen 3.

I know several theories, but in all these theories there is no regularity that would serve as proof, but there are only facts that destroy these theories.

#1. Water pump fails and the engine overheats.
I saw a Prius at an auction that I started and it misfired for a few seconds. The coolant was at the bottom in the expansion tank.
The check engine light pointed to the water pump.
However. Many people had no problems with the water pump and the head gasket began to leak.

#2. The EGR system gets clogged.
There are examples when Priuses reached 200k without cleaning the EGR. I have 2 Priuses for parts, one is a 2010 with 190k miles, no head gasket issues, and the other is a 2013 with 260k miles. It will be interesting to remove the EGR cooler on both and see its condition.

#3. The Gasket Masters theory which you can listen to in the video on their YouTube channel.
In the comments, the owners report different mileages, from ~130k to ~300k when the gasket blew.

#4. The factory defect, the gasket itself or the engine design. Again, some people drive up to 200k miles in urban conditions, while others only drive up to ~130k miles at the same conditions.

#5. Several bolts are not tightened from the factory. This theory breaks down in the same way as the previous ones.

#6. The problem appears when oil consumption begins. The temperature in the cylinders rises.
The problem of oil consumption was also in Gen 2, however....

 

There you go Mendel. More proof that the EGR system has no bearing on head gasket life. I pity the fool (Mr. T quote on the A Team) that performs this unneeded, difficult maintenance on an otherwise well running car and end up f'ing it up.

 

My theory has been: when the egr starts to plug in the manifold, cyc 1 is the first to be blocked, increasing flow to cyc 2, causing it to run slightly lean, run hotter, etc. Not enough to be an issue by itself.

Throw in the oil consumption issues and now it's much more prone to pre detonation. Putting more stress on it

Now throw in old coolant that's gone slightly acidic eating away at the hg slowly

Probably other small factors too that all come to head at the same time.

I feel like it's more prevalent on the 10-12 years, but don't have any data to back it up other than my gut

 

Are there any other cars with known head gasket problems where EGR is the culprit?

My theory is the water pump loses effectiveness but doesn't throw a code...

 

I cleaned the EGR on a 2010 Prius with 131k miles. The cooler was pretty well clogged, but I wouldn't say anything about the intake manifold. The dark water was coming out of it for a long time while i was cleaning it, but the ports were not blocked and water was flowing easily. Someday I’ll get to the high mileage EGR and see how things go with it.

 

Borowing @Carall’s pic:

the colloquial name for what Toyota calls “pipe” is “cooler”, which is apt. Reduced air flow aside, how well is this cooling:

 

Thermal cycling after loss of gen2s coolant heat storage combined with excess carbon build up due to rings and poor egr design. Add a marginal head gasket seal and there you go. The only difference with a Corolla 1.8 is thermal cycling. All fixed in gen4 by Toyota.