What’s causing my engine rattle??

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Urbanexplorer, Jun 26, 2021.

  1. Urbanexplorer

    Urbanexplorer New Member

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    My Prius with 190k miles rattles intermittently on initial start up but never when the engine cycles from the electric motor. Sometimes, it just putters for a few seconds at start. Never any issues idling or staling. Throttle position and RPMs are good. The rattle has been bad enough to register a misfire code before. My fuel economy seems to fluctuate between good and mediocre, but I couldn’t say if the two are related and it’s not consistent. I can’t seem to figure what to do next…

    No codes except misfire on cylinders 1 and 3, though the codes were only thrown once. I changed the plugs, coils, fuel injectors, EGR, PCV, timing chain tensioner, fuel pump assembly, upstream and downstream O2 sensors, and VVT solenoid. I cleaned the throttle body and MAF sensor. I tested for head gasket failure—no issue. Battery banks all look good. I tested for vacuum leaks—no issue. I tested for timing chain slack—no issue. The only other thing I can think of is the VVT actuator. What else might cause the car to rattle at start???
     
    #1 Urbanexplorer, Jun 26, 2021
  2. rjparker

    rjparker Tu Humilde Sirviente

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    Head gasket. Early stages seem to seal up after it starts. Won't even rattle every time. If it was not a 2010-14 I would not say this but it has become an epidemic in these engines.
     
    #2 rjparker, Jun 26, 2021
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  3. ChapmanF

    ChapmanF Senior Member

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    I am not as sure about what causes these startup rattles as some people are.

    A big part of why is that I had the same startup rattle develop in my Gen 1, with the 1NZ engine, at 198,000 miles, and that engine wasn't ever known for head gasket issues, and didn't even have the system that some people are convinced is causing head gasket issues on the 2ZR, and indeed I had that car nearly 40,000 more miles after that until a Dodge Dakota drove into it, and there were never any indications of a head gasket issue.

    I also never did find out what was causing the startup rattle. It made a pretty alarming racket but no one was ever able to pin it down. I did notice some cam lobes in the valve train looking dry-ish, as if maybe there was some issue with the oil delivery to those points.
     
    #3 ChapmanF, Jun 26, 2021
  4. Grit

    Grit Senior Member

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    which plugs did you use to replace with and have you had to top coolant to full recently, or notice a significant level drop?
     
    #4 Grit, Jun 26, 2021
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    How did you test? Leak-down? Boroscope? Just that "test for exhaust in coolant" tester (aka block tester?). The latter is likely not going to tell you about the most common ailment: coolant leaking into cylinder.

    Engine coolant reservoir level stable?

    You swapped in new/clean EGR cooler/valve? Did you clean the EGR passageways in the intake manifold?
     
    #5 Mendel Leisk, Jun 26, 2021
  6. Peter123

    Peter123 Active Member

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    An alternate explanation for this rattle is that the piston rings are fouled. At startup the oil pressure does not overcome the resistance to flow caused by the fouled rings for several seconds. You get the noise until the oil lubricates the pistons. If this is your problem, it should be more noticeable when you leave the car off for several days. All the oil drains down into the oil pan. Then your startup will be drier and noisier.
     
    #6 Peter123, Jun 26, 2021
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  7. Urbanexplorer

    Urbanexplorer New Member

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    I used iridium plugs (Denso if I remember right) which came pre gapped since you can adjust them though I measured the gap still just to ensure the gap was correct before installing. I did have a drop in coolant, but only because I recently replaced the thermostat and water pump--some lingering air bled the system, and I had to top up about 8-12 ounces. Out of an abundance of caution, I used a compression leak detector, and the results were negative. No white smoke either.
     
    #7 Urbanexplorer, Jul 8, 2021
  8. Urbanexplorer

    Urbanexplorer New Member

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    I did a basic compression test, and I used a compression leak test (block tester). Neither indicated a head gasket issue. The coolant has gone done a bit, but only about 8-12 ounces which is most likely because I recently changed the water pump and thermostat recently. The engine oil is very clean (no signs of contamination), and no white smoke. I removed the entire EGR assembly. I cleaned all the tubing and EGR cooler housing. I replaced the EGR itself. I cleaned the entire intake manifold and reinstalled everything with new gaskets.
     
    #8 Urbanexplorer, Jul 8, 2021
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