What Causes EGR Clogs?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Rebound, Dec 4, 2016.

  1. Rebound

    Rebound Senior Member

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    I cleaned the EGR pipe on my car at about 90,000 miles. It was very clean... some black carbon flakes. The pipe was nowhere near clogged, which makes me think the EGR itself isn't clogging.

    But I've seen photos of EGR's which had very wet, oily black clogs. What causes this, as opposed to the dry black flecks on mine? Oil getting past the piston rings?
     
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  2. Raytheeagle

    Raytheeagle Senior Member

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    My suspicion is the oil that leaks by as part of the Atkinson style engine and the location of the egr return into the intake manifold. Since the return is a low point inlet in the path of the system, it will collect oil as well as below the throttle body. I know there was a redesign done in 2012, but I only have experience with the 2010 version.

    Maybe the redesign repositioned the egr return, but I believe it was a volumetric change that was done in response to reduce the cold start knock, rattle and shake.

    Upstream of the egr, unburned hydrocarbons from incomplete combustion are the cause. This then recycles and mixes with the passed oil in the intake manifold and forms a nice mess. Early in a cars life it should be just the unburned hydrocarbons, but as the car ages and tolerances expand, the problem should get worse.

    That's at least my guess.

    I am trying to combat this by:
    1. Monitor gas mileage (I know what I should be getting based on usual driving habits on the same driving route and if I see a slow decline, consider a cleaning of the system)
    2. Monitor engine and motor transition and if there are any codes
    3. Using top tier gas
    4. Monitor oil level frequently
    5. Fuel injector cleaner every so often
    6. Engine oil treatment every so often
    7. Change out PCV valve and egr assembly every so often (did this at 120 k and will do it at 200k with the engine coolant change)
     
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  3. Rmay635703

    Rmay635703 Senior Member

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    Egr plugging is caused by exhaust gases being coked.

    As you surmise it could be oil or engine condition, but usually it has to do more with how many short engine runs you have done and how often you are running in "cold" weather.

    As the motor ages plugged egr becomes more common.
     
  4. Mendel Leisk

    Mendel Leisk Sand Pounder

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    #4 Mendel Leisk, Dec 4, 2016
    Last edited: Dec 4, 2016
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  5. Rebound

    Rebound Senior Member

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    I think that would cool the exhaust gases somewhat before they hit the EGR. Engine coolant circulates through the Gen III EGR. This can't work too well because I think that coolant's been heated by the engine already. This must put a lot of stress on the EGR, and moving it downstream undoubtedly helps. I don't know if they cycle coolant with the EGR located down there.

    EDIT: I've read a little more, and apparently the Gen IV puts the EGR pipe downstream of the catalytic converter in order to pipe cleaner exhaust gas into the intake manifold.
     
    #5 Rebound, Dec 4, 2016
    Last edited: Dec 4, 2016
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  6. Raytheeagle

    Raytheeagle Senior Member

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    I believe one of the "benefits" of the egr system with engine coolant was a reduced warm up cycle as the exhaust would help warm the coolant up to operating temp.

    The post cat recycle would be cleansed and seems better designed.
     
  7. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Independent of EGR there is also engine coolant being run through the exhaust, specifically to warm it, speed engine warm up. Can't remember the name of that circuit tho.

    Someone here doing a coolant change pulled off one of it's hoses, got significantly more coolant out. It's at a low point. You can see that component when the car's up for an oil change. Again, the name escapes me.

    Edit: Mind like a sieve, can't remember my own posting :rolleyes::

    Does Anyone Know How Exhaust Heat Recovery and Recirculation Works? | PriusChat
     
    #7 Mendel Leisk, Dec 4, 2016
    Last edited: Dec 4, 2016
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  8. Weasle543

    Weasle543 Member

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    You should see what EGR and a horribly inadequate air/oil separator in the crank case breather do to the intake manifold of an old Mk3 or 4 TDI.


    Posted via the PriusChat mobile app.
     
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  9. Raytheeagle

    Raytheeagle Senior Member

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    At least it was over 2 years ago. I sometimes forget was I had for lunch the day before :rolleyes:.
     
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  10. anonymous

    anonymous Member

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    Does PCV contribute to EGR clogging, and would installing an OCC prolong the endurance of the system?
     
  11. Aaron Vitolins

    Aaron Vitolins Senior Member

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    What about completely venting the PCV to the outside engine bay, and plugging the vent to the throttle body? Yes bad for the environment, but what do y'all think about that?
     
  12. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I think so: it's dumping oil into the intake manifold, which I'd suspect is ending up in the combustion chamber, and from there it's a short trip to the EGR intake. It's also oil-drenching the MAP sensor, not sure exactly what that's doing, but can't be good. An OCC stops that, at least most of it.

    Meh, go the Oil Catch Can route, be one of the good guys. (y)
     
  13. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Makes total sense!
     
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  14. Mendel Leisk

    Mendel Leisk Sand Pounder

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    They used to say that you could see upcoming bumps in the road, by the oil patch just beyond them. Every car that hit the bump would tend shake loose a drop or two of oil. Maybe this doesn't happen as much since the advent of PCV valves. I guess there's lots of oil leakage still, oil pan gaskets for example. Yeah, just musing.

    Right after I installed my Moroso oil catch can (85474 Air-Oil Separator), I neglected to close the drain tap on the bottom. Driving around the block I noticed a subtle but definite tone under certain acceleration conditions, thought uh oh...

    Fixed that right away. Was think that was like a crankcase vented to atmosphere condition. But there's still a difference: It's also an intake manifold vented to atmosphere condition, not good, and likely the source of that sound.
     
    #14 Mendel Leisk, Aug 12, 2018
    Last edited: Aug 12, 2018
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  15. Tande

    Tande Active Member

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    Or breakfast this morning! .......;)
     
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  16. anonymous

    anonymous Member

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    I thought about that. If the engine leaks oil anyway then I figured some more oil wouldn't be a big deal. But it also includes hydrocarbons and would stink. I would just go with an oil catch can since it's simple enough.

    Oh, there also might be a problem with a lack of vacuum to pull gasses out of the crank case. Older cars that did vent to the atmosphere used a draft to pull the gasses out; see Crankcase ventilation system - Wikipedia . If the PCV end was just open it could cause rapid sludge build up.
     
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  17. anonymous

    anonymous Member

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    heh, yeah, an intake leak can really mess up the control of the engine. If the leak is big enough the computer will give up trying to run the engine and will leave you powerless.
     
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