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Expected mpg improvement from EGR etc cleaning?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by PriusNeckBeard, Jul 14, 2022.

  1. ASRDogman

    ASRDogman Senior Member

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    I watched a video of someone replacing it through the wheel well and headlamp removed.
    But I cannot find that video anywhere. I was certain I bookmarked it, but it's nowhere.

    I will just have to give it a try soon and see what I can do.
     
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  2. jerrymildred

    jerrymildred Senior Member

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    I've tried to find videos of it, but struck out. After looking at it on a Gen 3 yesterday, it looks like it might be possible from below except that the hoses connect at the top. Maybe you can get there through the wheel well. I didn't look at it that way. At any rate that thing is a big downgrade from the Gen 2 in terms of ease of maintenance.
     
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  3. MikeDee

    MikeDee Senior Member

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    Excuse me if this has been explained elsewhere, but why would a clogged EGR system cause head gasket failure? If this service were so important, why is this not in the maintenance schedule in the owners manual?
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    The exhaust gas returned to the combustion chambers has less oxygen, so modulates the the explosions. It reduces emissions and allows more efficient engine operation.

    Just my take: Toyota's engineers are counting on proper operation of that system. If the exhaust gasses are virtually blocked, due to carbon clogging, the engine will run hotter, the head, it's bolts, and the gasket. If the blockage is uneven (typically the EGR passages in the intake manifold fully clog in a sequence, commencing with cylinder one, and so on), then you get uneven increase in heat. The 3rd gen head gasket failures are virtually always at the adjoining wall between cylinders one and two.

    For a lot more info, Google "Exhaust Gas Recirculation wiki".

    More likely this would be included in the Warranty and Maintenance Booklet, in the States. The reason it's not is fairly simple: the engineers did not foresee this happening. Likely due to rushed production deadlines, insufficient testing.

    And once it started cropping up, instead of doing the right thing, Toyota "circled the wagons". The did issue a Warranty Extension Notice, which says if you get shakes at cold-start and/or the code for EGR clogging, they'll fix it. There is no mention of head gasket failures, they don't want to make a connection, at least not publicly. Also in that document, there is the statement, in italics and underlined:

    While the majority of vehicles will not experience this condition

    If you're questioning someone, you suspect they're being evasive, you can give them a "bait question", see if they answer truthfully. Here there was no need, Toyota's lying, upfront, with that statement. They all clog.

    The sad thing for 3rd gen owners: if you trust and follow Toyota's guidance, wait for the cold-start shakes and code, your head gasket is already failing.

    Other confirmations of the EGR/head gasket correlation:

    There's 3rd gen owner reports here, after head gasket failure and replacement, but without thorough EGR cleaning: 20K or so later, the head gasket fails again.

    Fourth gen has an EGR system with crucial revisions (learned at the expense of 3rd gen owners), and they are very effective. @jerrymildred (working for Tampa Hybrids) was cleaning a 4th gen EGR system. IIRC the car had around 360K miles on it. The cleaning was a waste of time; the system was no where near clogged. Also, I don't think there's been ANY 4th gen head gasket failures confirmed here. OTOH, 3rd gen head gaskets fail reliably, anywhere between 125K and 200K. If the EGR is not regularly cleaned.

    My 2 cents:

    Toyota should have amended the maintenance schedule, instituted a (hopefully gratis) regimen to keep the EGR systems functional, through regular cleanings, published a Technical Service Bulletin outlining how dealership service departments could do this, without just wholesale parts replacement. Say every 50K miles.

    Instead they've kept quiet.
     
    #64 Mendel Leisk, Dec 1, 2022
    Last edited: Dec 1, 2022
  5. ASRDogman

    ASRDogman Senior Member

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    It IS a stupid place to put it! I seem to remember moving or removing the wheel well
    plastic trim and being able to reach it from there. And I "think" the loosened the inverter
    mounts and were able to raise it up to reach into it, without having to remove all the cables.
    Just pull the plug on the battery housing so no power is going to the inverter.
    That's how they got to the hoses and bolts. I have several types of fancy tools to reach in to
    get to both.
    I guess I'll just have to start it and figure it out as I go.

    Thanks for the info! (y)

     
  6. ChapmanF

    ChapmanF Senior Member

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    There's been little presented here, ever, to support the notion that the mechanism (if present) is this general increase in heat. A person who wanted to find out would ask and then answer three questions:

    • By how much do the head, bolts, and gasket temperatures increase because of lack of EGR? (A)
    • What temperature becomes damaging to the gasket? (B)
    • Is the temperature resulting from A less than, equal to, or greater than B?

    In all the years of EGR discussion here, those questions have been avidly avoided, the way our dogs when I was a kid would avidly avoid noticing snakes.

    There is, however, another effect on combustion when EGR is reduced (and the spark timing isn't protectively backed off in response): detonation, which is known to be capable of causing such damage, and is expressly mentioned as a risk in technical literature about EGR. So, if there is a connection in the Prius between EGR issues and head gaskets, this would seem more likely to explain it.

    At the same time, there exist at least one or two other schools of thought on PriusChat that attribute Gen 3 head gasket issues to other causes than EGR.

    One important thing for Gen 3 owners to remember is that the Prius drive train will make any misfiring for any reason sound absolutely awful. Yes, if you have it specifically on cold starts after long sitting, a head gasket issue can be among the things it makes sense to check for. But people can and do find misfiring also to be caused by other things, even misfiring on cold start. So when we descend like locusts on every new poster with a shaky engine and declare their head gaskets blown sight unseen, we are rushing them into significant expense.

    I've read through one thread here that fits that description; Mendel's mentioned it often. It is suggestive, no question. Threads plural would be more so. I don't see every thread, so maybe the one did later become plural; I'm sorry if I missed it.

    Fourth gen has an EGR system based on research that was being done industry-wide during the development and run of Gen 3, covered in easy-to-find publications from that period. The differences, including changes in gas pressure and chemistry and the effects in the combustion chamber, can all be read about. The research included, naturally, whether the new approach would be worth switching to from the previous state of the art, which Gen 3 has. The results were mature enough, by the time Gen 4 was in design, for Toyota to make that switch.

    Toyota sold around two million Gen 3 liftbacks, 600,000 Prius v, and not quite 100,000 PiP. Any claim about how "reliably" their head gaskets fail, and at what mileage, has to be calibrated by comparing the number of such reports we have ever seen to the number of the cars out there.

    Because regular EGR cleaning is an enthusiast activity promoted on sites like this one, and the vast majority of Prius owners have probably never heard of it, it probably is true that head gasket failures, when they happen, are mostly happening in cars where it hasn't been done. They are probably also mostly happening in cars that haven't regularly had their headliners waxed.

    Mendel has been long aware of all the points above and persists in writing posts as if he is not. And has a free-speech right to do it, but it kind of sticks out if someone's going to fling accusations of lying and wagon-circling in other directions.
     
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  7. CR94

    CR94 Senior Member

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    The notion that general increase in temperature resulting from impaired EGR is a factor is far-fetched, according to my knowledge and opinion. Heat transfer from gases within the cylinder to the chamber walls depends less on the momentary peak gas temperature than the average temperature through the entire cycle (although "average" is a simplification of a complex function). The gasket isn't getting hotter than normal. Momentarily abnormally high cylinder pressure from detonation likely is a factor. So is uneven thermal expansion of block and head, aggravated by the frequent stops and starts inherent in hybrid duty.

    The head gaskets may "fail reliably," but I hope mine is one of the ones that go a long way before that inevitability strikes.
     
  8. OptimusPriustus

    OptimusPriustus Active Member

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    High load is more efficient. Thats why pulse and glide works. The mpg record vehicles generally have tiny engine that is maxed out and then shut down for gliding. They run that cycle continuously as far as i know.

    i dont know but i would guess Prius engine try to take advantage of the high load = better efficiency in some way. I’d be surprised if it doesn’t. They’ve explored almost all possible ways to optimize mpg

    and turbocharged cars are high loaded when flooring. In normal driving there’s no 2bar charge:)
     
    #68 OptimusPriustus, May 21, 2023
    Last edited: May 21, 2023
  9. MikeDee

    MikeDee Senior Member

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    The Corolla uses a similar engine. It uses the Otto cycle instead of Atkinson. It puts out more horsepower and hence the combustion temperatures and pressures are higher. The same head gasket design is used and probably the same flawed EGR system, yet it does not blow head gaskets with the frequency that the Prius does. Also, Priuses that are mostly highway driven don't experience the problem with the frequency that city driven ones do. Obviously there's some other cause at work here, and my money is on temperature cycling. Seems obviously to me. The usual cause of overheating and corrosion failing head gaskets shouldn't be ignored either. How many of these Priuses with failed head gaskets had their coolant replaced at the proper interval with the proper coolant?

    I'll probably have my EGR system cleaned at 120K miles when the spark plug change is due or there is a CEL or drivability problem. Otherwise if it ain't broke don't fix it IMO. A number of people have posted here that have screwed up a properly running vehicle by attempting this complex and time consuming repair themselves so I'm not going to go there.
     
    #69 MikeDee, May 21, 2023
    Last edited: May 21, 2023
  10. OptimusPriustus

    OptimusPriustus Active Member

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    Here’s how my valve looked like after 130kmiles. No CEL (amazingly) and car worked fine. It was a surprise to mechanic as well. He was not familiar with Prius

    F52F00BE-8322-4E93-A1DA-60D8A8F86EE4.jpeg

    Edit: 6kmiles after cleaning valve stuck open and i replaced it.
    3EA79408-53EB-4063-B9DC-13EF010508F7.jpeg
     
  11. CR94

    CR94 Senior Member

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    Yes, it does, in multiple ways (Atkinson cycle + keeping engine speed as low as possible + ... )