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Cylinder leakage test at 124,000 miles

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by ChapmanF, Jul 30, 2017.

  1. ChapmanF

    ChapmanF Senior Member

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    At the same time as changing my spark plugs ('cause, who'd want to do that much work twice?), I took my first leakage readings on this Gen 3 that I bought used a little over a year ago. (I'd love to be able to get leakage numbers before buying a used car, but what seller would stand for the amount of disassembly it takes to get down to the plugs?!).

    A cylinder leakage tester is an alternative way to get roughly the same information as a compression test, but instead of cranking the engine, you hold the crank stationary and use compressed air. The tester has a gozinta where you connect your compressor, and a gozouta to the spark plug adapter, with a restriction in between, and two pressure gauges, one upstream and one downstream of the restriction. The drop between the two readings indicates the leakiness of the cylinder. Because it doesn't involve cranking, it's very quiet, and if there's excessive leakage, you can even kind of listen for where it's going (out into the intake or exhaust manifold if a valve is sticky, or into the crankcase, or bubbling out in the coolant...).

    Of course Toyota doesn't publish standard leakage-test figures the way they do for traditional compression tests, so it's most useful to compare to baseline readings from very early in the engine's life, or just to see how well the cylinders balance. Makers of these leakage testers don't have a standard spec for the restriction size (well, FAA does, for testing aircraft engines, but in the automotive world, no), so it's hard to compare readings between different testers. I used an OTC 5609.

    You turn the crank by hand four times, to get each cylinder to compression TDC, and then you need a way to hold it there (because unless you miraculously found exact top-dead-center, the air pressure will try to spin it around). I found Gen 3 has enough room to feed my breaker bar right down from above, under the hood, with a 19mm socket on the end for the crank bolt, and then I just cinched a little nylon strap around the breaker bar handle and the engine mount.

    A little disconcertingly, though, I got three excellent readings and one lower one ... kind of a letdown, as, going through in firing order, the low one (cylinder 2) was the last one I came to. :(

    The readings were: cylinder 1 (100 psi left gauge, 98 right), 3 (100 -> 98), 4 (100 -> 98), 2 (100 -> 91). The sound of airflow was almost inaudible for the first three, but noticeable for cylinder 2. The escaping air seemed to end up in the crankcase.

    This is still (barely) in the range of cylinder variation that the OTC 5609 instructions consider tolerable (says to investigate further if there's a 10% difference). And for what it's worth, these were measured more or less cold. (OTC recommends operating temperature, but I didn't plan well, and if the engine was warm before I started pulling off covers, wipers, etc., it wasn't very by the time I tested.)

    The car doesn't have any noticeable power loss or imbalance symptoms, and all four plugs came out in identical condition with identical deposits. Still, I wonder why I'd have one cylinder that different at just 124,000 miles.

    I remember my old Gen 1 had all four cylinders within 1% when I tested it the first time, around 206,000! However, by about 20,000 miles after that, it had two cylinders low (100 -> 93 and 100 -> 89). But shucks, that was at 226,000 miles, not 124,000....

    Maybe I need to find a skinnier inspection camera and see if I can get a view inside cylinder 2. The one I've got won't fit through the spark plug hole.

    -Chap
     
    #1 ChapmanF, Jul 30, 2017
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  2. m.wynn

    m.wynn Senior Member

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    Chap,

    I'd recommend you de-carbon/sludge the entire EGR circuit as per any of the DIY threads. Although 124k is low for actual blown head gaskets, it's not unheard of. ~175ish is my casual observation of where most of the lower end mileage failures occur, but we've seen as low as ~30k in a Gen 1 PiP, and a handful of Gen 3's under 100k. My 2010's IM was fully blocked and the car shuddering at light throttle acceleration at 97k miles. The EGR valve and cooler were still only partially blocked at 140k. My thinking is the IM will sludge up first if the car burns no oil, being the "cold" end of the circuit. Oil burning speeding the whole mess and further blocking the EGR cooler/valve seems logical to me but who knows. It will be an easy procedure for you technically but budget 4-6 hours minimum.

    @Raytheeagle has a slick little PDF of all gaskets needed. Add a couple gallons of SLLC (or even 1 gallon for a partial drain) and an E8, external torx socket or ratcheting end wrench and you're ready to rip and tear.
     
    #2 m.wynn, Jul 31, 2017
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  3. ChapmanF

    ChapmanF Senior Member

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    I have seen the other threads on EGR cleaning. I didn't add it to the agenda for this weekend, but probably will get to it. My past vehicles with EGR had recurrent cleaning headaches, so it stands to reason.

    If possible, I'd like to keep this thread on the topic of cylinder leakage / compression readings, maybe even whether anybody else takes them proactively and what readings are being seen at what mileages. There don't seem to be as many threads about that.

    -Chap
     
    #3 ChapmanF, Jul 31, 2017
  4. mjoo

    mjoo Senior Member

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    From what the techs are saying on PC about the Prius engine, the piston rings are low tension with less material that prior years. This was meant to reduce the internal friction but results in faster gumming up of the oil control ring...

    Have you tried a piston soak? There are lots of success stories with piston soaks on bobistheoilguy.com. IMO anyone that replaces the spark plugs should do a piston soak from all the engine oil burning stories we hear on PC. Don't forget to siphon the oil out of the cylinder(s) after the soak is done before starting the engine.

    Also have a look at the reviews for this product:
     
    #4 mjoo, Aug 4, 2017
    Last edited: Aug 4, 2017
  5. Michael Cerkowski

    Michael Cerkowski New Member

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    On a related but different note: we just had a diagnostic leakdown test done on our 2013 PIP, and the result for cylinder one was '50% leakage on intake side'. They want to inspect the intake valve spring. Is this a known Gen III issue?
     
    #5 Michael Cerkowski, Dec 4, 2019
  6. bisco

    bisco cookie crumbler

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    not the valve spring that i can recall, but lots of head gaskets
     
    #6 bisco, Dec 5, 2019
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  7. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    I wonder what they mean by that? Intake valve not seating I'd guess. If you repeated the test with the intake manifold removed you'd be able to hear it I think.
     
    #7 Mendel Leisk, Dec 5, 2019
  8. ChapmanF

    ChapmanF Senior Member

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    Ought to be able to hear it without the manifold removed ... that's what makes the leakdown test so handy. You already know which cylinder you've connected the tester to, and if the throttle body is where you hear the hissing (more than in the crankcase, exhaust, or bubbles in the coolant), you pretty much know what you're hearing.
     
    #8 ChapmanF, Dec 5, 2019
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  9. Paladain55

    Paladain55 Active Member

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    I would say the intake valves and cylinder on cylinder 1 in my prius had the most carbon build up. So its gotta be related to the way the EGR circuit clogs up I would want to think. It seemed like there was also enough carbon build up and sludge on the valve that it would interfere with the valve seat and valve seal as well. I would think the sludge being slightly gritty would wear out valve seals faster as well.
    So say if cylinder 1 expects to get a certain amount of EGR but doesn't the mixture would be more off than the others as you go down the line. So would that make cylinder 1 run rich?
     
    #9 Paladain55, Nov 16, 2022
  10. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    I observed the same: intake manifold EGR passage at cylinder one "led the pack" in carbon clogging. I suspect this will make it run hotter. The majority of head gasket failures are on the adjoining wall between cylinder one and two.
     
    #10 Mendel Leisk, Nov 16, 2022
  11. Paladain55

    Paladain55 Active Member

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    Also, to add you will have a ton more blow by as a result of all the increased carbon buildup. Blow by into the crankcase outside of the cylinder is a factor in blowing out seals so it can do it to headgaskets as well

    Wait so actually a lack of EGR would make me think leaner. Because you would be getting more burnable air than expected. Leaner also destroys cylinders like with aftermarket tuners who go too lean on their sporty tunes. Leaner = hotter as well as the fuel does cool the cylinder
     
    #11 Paladain55, Nov 16, 2022
  12. CR94

    CR94 Senior Member

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    The fuel/O2 ratio wouldn't change, but the tendency to knock in that cylinder would increase with lack of expected EGR gas.
     
    #12 CR94, Nov 16, 2022
  13. Paladain55

    Paladain55 Active Member

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    So even though you're replacing egr gas that has very little burnable o2 in it with fresh air with burnable o2 in it the ratio wouldn't change? I agree the lack of expected egr is bad
     
    #13 Paladain55, Nov 16, 2022
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  14. CR94

    CR94 Senior Member

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    Hmmm... On further thought, you may be correct, at least partially. That would mean the other cylinders are getting a (slightly) richer mixture than expected, since each injector should inject ¼ the quantity appropriate to overall air flow, eh? Interesting question.
     
    #14 CR94, Nov 16, 2022
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  15. mjoo

    mjoo Senior Member

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    Nonsense...

    moto g power ?
     
    #15 mjoo, Nov 17, 2022
  16. Paladain55

    Paladain55 Active Member

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    Me personally since we don't have a wideband o2 connected to each exhaust port to see the changes, I would think they are all running leaner and hotter to a certain degree and the combustion conditions is wrong for all of them.
     
    #16 Paladain55, Nov 17, 2022
    Last edited: Nov 17, 2022
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