Hello, I have a hypothetical question for the brain trust here. My best friend and his girlfriend live in Washington State, far from me. In a few weeks they are starting a big trip around the country, first to California for rock climbing near Bishop for a few weeks, then making their way over to West Virginia some time in March, and they hope to get up to me in Southern Maine at some point in April. That is like 4,250mi just to get between those places. All in their 2010 Prius with about 200K on it. When I heard this I felt a little devil jumping on my shoulder shouting "Head Gasket! Head Gasket!" If I lived nearby I would go over with my spare clean intake and EGR cooler to swap them out before their long trip. The thought of being on the road and having their only car need a head gasket/new engine does not sound fun! Some of you may say: "Even if you swapped them now it may be too late for that gasket and the damage has been done but yet to be noticeable." True, but that does not seem like a reason to AVOID maintenance. My friend is not afraid of wrenches, but it is not something he relishes in his free time. Thinking of the two tasks, swapping out an intake is much less involved than doing the same with an EGR cooler. Last night I thought to myself: Hey, what if I ship him my cleaned intake and then at least the EGR passageways are not clogged? So my question is this: What do we postulate the effect may be of only cleaning the intake? My understanding is that what contributes to head gasket leaks is the overheating of cylinders 1 & 2. So, if the flow to each cylinder is equal (though probably very little given the expected state of the EGR cooler) would there be any head gasket protection?
There are different understandings floating around; the idea that it's about simple overheating as a result of bad EGR flow does not seem to have very good support. The engine's cooling system takes much larger changes in heating in stride whenever you go from down a hill to up a hill. Another effect you could expect from imbalanced EGR flow in the four passages would be a combination of: misfiring in the cylinders getting more flow, and possible detonation in the cylinders getting less. The ECM only sees one feedback value for overall flow, so with those passages differently clogged, when the feedback looks like correct flow, there must be cylinders getting too much and others getting too little. When the ECM thinks the overall flow is too low, it takes other measures to protect against detonation, but when, as far as it's concerned, the flow is fine, it doesn't, and that would put in danger the cylinders getting too little flow. It is easy to find engineering literature connecting detonation to gasket damage. The other idea, that it's about simple overheating, is often mentioned here but not so easy to find in the literature. In any case, yes, if the manifold hasn't been looked at, and there isn't time to do the whole EGR system, the effort to do just the manifold can still be very well spent. The manifold is the only part of the EGR system where the flow can be wrong without the ECM noticing. I would be remiss not to also mention what Toyota seems to think is behind the head gasket problems: TSB EG-0127T-1014 (SW update to avoid cylinderhead gasket failure) | PriusChat They think they programmed the ECM wrong as far as the speeds it chooses for the variable-speed water pump. The gist seems to be they think they run it too slowly at times, so the temperature in some hot places of the engine can get much hotter than the reading you see from where the sensor is. That's a European TSB, and talks about newer firmware versions where they fix that. They don't seem to ever have released a US TSB that quite comes out and says anything that clearly, but there have been two different US TSBs (T-SB-0103-12 and T-SB-0027-16) that plug the same new firmware versions while keeping mum about what was actually changed. I strongly suspect that it's not a bad idea in the US to be running those updated versions, and a quick ECM flash, if the recommended version isn't what's already there, might also be something there is time for before beginning the long journey. Again, it's probably true that updating the firmware now doesn't reverse 200k miles of running with the old firmware. But sooner is probably still better than later.
Why are my ears burning? It is not hard to clean an intake, I wouldn't bother shipping him yours, but he should do it asap. As Dylan said, it doesn't take a weatherman, to know which way the winds blowing. He should clean the whole thing at earliest opportunity, but brace for head gasket failure as well.
