If I was experiencing the symptoms of a blown head gasket

If you look at the posted intake manifold pics, showing the degree of egr passage clogging, they invariable are most clogged at cylinder one, and that is where the head gasket failures are being reported, almost without fail.

The analogy that keeps coming to mind for me, is Ambassador Graham Martin, and the fall of Saigon.

 

Say, there's an interesting observation. Are you suggesting there might be four small passages downstream of the EGR cooler, the EGR valve, and the MAP sensor that confirms overall EGR flow, and that possibly differences in the occlusion of these four small passages could lead to differences in the fuel charge entering the four cylinders, but that the engine control module wouldn't have any way to know about these differences, so maybe it wouldn't apply the timing retard that it normally would as protection from reduced EGR flow, and as a result maybe one cylinder might be more prone to detonation, say, than the others?

Whaddaya know, a third possible mechanism to try to fit to the data. We've had the "cooler clogging reduces the overall flow so higher engine temperature so head gasket", and we've had the "coated cooler passages don't extract as much EGR heat into the coolant so higher engine temperature so head gasket", and now we've potentially got "differential occlusion downstream of the cooler and valve leading to undetected mixture differences between cylinders, defeating ECM's strategies to protect against detonation."

Do you think it might be interesting or worthwhile to try to figure out which of those mechanisms might be more plausible? I mean, the first, overall-heat one seems to leave some obvious questions unanswered, and the second, with the cooler heat transfer, seems even a little more far-fetched (what could be the maximum difference in temperature extracted through a six-inch HX with hot coolant, and how does that compare to the energy of combustion?).

Now this third possibility, this seems to have a few advantages. For one, it's pretty hard to find literature saying that the overall temperature of an engine without EGR is going to kill head gaskets. But it's not hard to find literature associating detonation with engine damage, including head gaskets. If it's a matter of difference in occlusion, which can't be detected by the single MAP sensor, it could explain damage being done before the ECM has intelligence of an overall EGR deficiency.

And it would kind of even lead to the observed pattern you're pointing out here, right?

It would still take more work to call even that proposed mechanism really established, but so far it seems to have a bit of an edge over the others.

Is there any point in bothering to distinguish between possible mechanisms or figure out which one might be more likely? Well, kinda yeah, right? Because it's way easier to check the intake manifold for differential occlusion of those four small passages, and ream them out, than to do the whole ritualistic stem-to-stern business most people are being frightened into. If it could be established that most people could get by with checking and cleaning their manifold and asking the car whether it's necessary to dive further in, a lot of people might find a half-hour job suffices instead of a grueling weekend job that can be put off a lot longer if they are watching the flow numbers.

So there's a reason it might be interesting to care a little about what the reality might actually be.

So Graham Martin was the ambassador who persistently ignored signals intelligence saying that North Vietnamese were preparing an attack on Saigon.

Only here, we've got a situation where it's in everybody's interest, including the ambassador's, to sit down with the intelligence, and actually look at it, and try to figure out what kind of attack is being planned and what's the most effective way to respond to it, only there's one guy who keeps barging into the conference room and shouting they're going to attack using sharks with laser beams on their heads.

He gets asked on what actual intelligence he is basing that, and he pretends not to hear the question, leaves the room, barges in a different door wearing a different color shirt and sounds off about the sharks again. All while it might be really useful to work on learning more about the real threat and possible effective countermeasures.

Has the possibility of a differential-occlusion-leading-to-detonation mechanism ever been raised here before? Oh yeah, it was ... by Ambassador Martin. You were even there at the time.

 

Yes on my 2013 prius V (175K miles) HG failed and it was cylinder number one. The intake manifold leading into cylinder number one was positively coated and dripping with oil. But there was no oil on other parts of intake manifold leading to other cylinders. So what you said makes perfect sense, about egr passage cloged in cylinder one leads to oil pooling in cylinder 1 and eventually head gasket failure in cylinder 1 due to pooling of incompressible oil. If I have catch can installed between pcv valve and intake, will that eliminate oil pooling EVEN IF egr passages were clogged on cylinder 1? Going by the fact that catch can should remove most of oil from pcv valve, it seems likely that it will greatly reduce chances of another HG failure.

 

Clean Exhaust Gas Recirculation passages, from start to end, are imho paramount for preventing head gasket failure. The PCV oil dump may contribute, by introducing oil in combustion chamber, that burns and maybe contributes to the EGR carbon build up.

With semi-regularly cleaning of the full egr system, plus an effective oil catch can, I believe you WILL avoid head gasket failure.

 

Can go a little further into the connection you've got in mind here?

I don't remember seeing Mendel or anyone else suggesting a connection between EGR passage clogging and oil pooling. What you tend to find in the small EGR passages will be a dry accumulation of carbon.

Where exactly were you seeing the "coated", "dripping" oil? It sounds like an interesting observation and there might be a good story behind it, but I'm not sure that will be a story about EGR.