Engine knock under heavy load and at high temperature

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by whodat, Jun 14, 2015.

  1. whodat

    whodat Member

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    Hi Prius Enthusiasts
    I am the original owner of a 2006 Prius with 265k miles. I use Mobil 5-30 synthetic oil and I drive a steep hill every day and the engine knocks in the summer afternoons when I use cheap 87 Octane gasoline from Safeway or Costco. If I use better 87 octane gasoline (Chevron, Shell) generally there is less knocking. Also during the winter months no knocking even with cheap gasoline.

    During summer I can sometimes make the knocking go away by accelerating or decelerating. The knocking is intermittent and generally occurs only during the steepest parts of the commute. The engine might knock for 30 seconds to 60 seconds before its goes away as I try to change the engine RPM.

    Unfortunately I am burning some oil at a rate of approximately half a quart every 5k miles. Generally I watch the oil level, but there have been cases where the oil level has fallen below the lowest mark on the dip stick so I suspect I have some carbon build up.

    I've read posts where others have used additives like gumout regane and I've read posts that say not to use additives.

    I've also read I may be damaging the engine when knocking occurs.

    Should I have the anti-knock sensor checked/replaced? Should I start using higher octane gasoline?

    Thanks
     
    #1 whodat, Jun 14, 2015
  2. bisco

    bisco cookie crumbler

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    there must be anti knocking compounds in those higher quality gasolines. what is the cost difference, 25 cents?
     
    #2 bisco, Jun 14, 2015
  3. KennyGS

    KennyGS Senior Member

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    I would switch to higher octane for a while and see how it goes.
     
    #3 KennyGS, Jun 14, 2015
  4. xliderider

    xliderider Senior Member

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    You have a high mileage Prius, search for EGR valve cleaning. The Atkinson cycle apparently causes a lot of fouling in the EGR valve and associated hoses and intake manifold which causes knocking and engine misfires.

    Edit: Here's the thread.

    Prius III engine knocking at high torque low RPM (solved) | PriusChat

    Edit 2: I see you have a Gen 2, but I hope the Gen 3 link helps.
     
    #4 xliderider, Jun 14, 2015
    Last edited: Jun 14, 2015
  5. valde3

    valde3 Senior Member

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    There is not an EGR in gen 2 Prius. If higher octane gasoline fixes the nocking then engine has carbon buildup in combustion chamber.
     
    #5 valde3, Jun 15, 2015
  6. cyclopathic

    cyclopathic Senior Member

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    First of all Costco is Top Tier gas, not necessarily "cheapo".

    Are you burning oil or it is leaking out? IMHO if you're planning to keep car running it may be worth to replace valve stem seals with quality nitrite rubber.

    With respect to knock sensors I'd get a OBDII plug ($5), Torque app ($5) and see what they are reporting. New sensor is $60-120, and $10 on diagnostic tools which will work on all your cars is small price.
     
    #6 cyclopathic, Jun 15, 2015
  7. wjtracy

    wjtracy Senior Member

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    If you live in California you are getting CARB/EPA reformulated gasoline, which means EPA sets the basic recipe and there is not much variation between brands. I guess nothing stops a company from putting say mid-grade octane in the Regular tank, but I'd expect the same octane and knock tendency. So the only thing that you can really do is add mid-grade or Premium to get the higher octane to get less knock. Of course you're car is causing the problem, but at 265k miles, it doesn't owe anybody anything.
     
    #7 wjtracy, Jun 15, 2015
  8. Aaron Vitolins

    Aaron Vitolins Senior Member

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    How you dip below the low mark on the dip stick if your car only burns half a quart of oil every 5000 miles? Did you go like 15,000 miles between oil changes? Sorry I'm confused! BTW your oil consumption rate is very low for a prius with high milage, congratulations! :)
     
    #8 Aaron Vitolins, Jun 15, 2015
  9. cyclopathic

    cyclopathic Senior Member

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    the Top Tier gas has about x3 times cleaning detergents, and the carbon build up in cylinders is responsible for knock.

    256k is nothing we have '96 Mazda with 430k with about the same consumption. I suspect as with many OHC engines issue with valve stem seal wear which causes excessive oil consumption
     
    #9 cyclopathic, Jun 15, 2015
  10. whodat

    whodat Member

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    I go 10K miles between Mobil 5-30 oil changes. I had my oil tested early on at 5K and 10K and determined it was ok to go 10k miles between oil changes based on the oil analysis.

    I could be wrong about the amount of oil burn. There are no oil leaks, its oil burning. About twice a month I check the oil level and add oil to keep the dipstick oil level closer to the upper mark.

    I had read a post saying that keeping oil closer to the lower mark gave better fuel economy, so previously I used to keep the oil level closer to the lower mark and that's how I found that I could actually drop below the lower level and that may have contributed engine carbon...
     
    #10 whodat, Jun 15, 2015
  11. 69shovlhed

    69shovlhed Surly tree hugger

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    knock sensor must not be working correctly. its supposed to tell the ecu if there's any knocking and the ecu will back the timing off.
     
    #11 69shovlhed, Jun 15, 2015
  12. whodat

    whodat Member

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    Update 7/5/2015:
    I have run 2 tanks of gas with higher octane 89 and 91 - no knocking nor engine clatter nor pinging. Bay Area, CA gas.
    So looks like I'm going to switch to 89 from 87 octane.
    Thanks for the advice and help.
     
    #12 whodat, Jul 5, 2015
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