WARNING: Don’t do this to your Prius that burns oil

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by M67v, Apr 26, 2021.

  1. M67v

    M67v Junior Member

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    (TLDR: DON’T USE 10W-30 OIL ON YOUR PRIUS. In fact, don’t use anything other than 5W-30 oil on your 2nd Gen Prius, even if it is burning oil)

    So I own a 2007 Prius, fully loaded, and it’s been over 2 years since I first got it. To be fair, my car was obviously mistreated by the previous owners, so my issue could in part have to do with that.

    However, when my car started burning through oil at a rapid rate, I was, well, quite alarmed. It started doing it around 178k miles, and so I bought a new PCV valve but never bothered to install it since it was expensive to do so and most mechanics refuse to work on a hybrid of any sort, let alone a Prius.

    So I just made a habit of topping off oil whenever it got low. I did read somewhere that using 10W-30 oil, a thicker oil, will slow down oil consumption. And so, I went ahead and put that in one time.

    Big mistake. Fast forward a few weeks later to present day, and the car out of nowhere starts misfiring like crazy. “What gives? I changed spark plugs and ignition coils not long ago,” I ask in my head. Then, the cabin is ripe with fumes of what I believe is unburned. Eventually, “knock-knock.” And who’s there? Oh no one, just the rods that want nothing more than to be put out of their misery.

    I was talking to my friend about this today, and I still don’t know what’s wrong. Then I told him about my oil consumption issue and how I used thicker oil. It was in that moment where he said, “That’s why your rods are bent fool. The rods couldn’t handle the thicker oil,” (he actually didn’t insult me like that but that’s pretty much how it went). It makes sense too. It’s an aluminum engine block.

    If you have an oil burning Prius, either top off oil whenever possible, or change the pcv valve. Either way, don’t ever put in any oil other than what the car calls for. Don’t use 10W-30, even synthetic like I did. Use the regular 5W-30 Synthetic. Otherwise, you might have a problem like I did. Now I have to sell it as a parts car since I can’t afford a new engine.
     
  2. JC91006

    JC91006 Senior Member

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    I don't think 10w-30 would have a catastrophic effect on a Prius engine. Your engine was well worn before you switched to this oil.
     
  3. Fred_H

    Fred_H Misoversimplifier

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    In the US, due to EPA regulations, most auto manufacturers specify energy saving motor oils. In many other countries, a choice of different oil viscosities are specified, depending on prevailing ambient temperatures.

    For example, in Germany 10W-30 is allowed for temperatures down to 0°F (-18°C) for the Gen 2 Prius.

    At temperatures above freezing, even viscosities as high as 20W-50 are allowed for the Gen 2 Prius.
     
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  4. TMR-JWAP

    TMR-JWAP Senior Member

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    :rolleyes:Sounds like it's time to seek advice from someone else..........

    Any chance you can go into this a bit deeper?
    It makes sense too. It’s an aluminum engine block.
     
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  5. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    My company doesn't use anything else for their fleet vehicles last time I checked....

    Oh and I think that I've identified the root cause for your trouble.
    You've had this mechanic for how long?

    Yeeeeaahh.
    I think that the "change mechanic" light just came on.
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    This is a joke, right ?
    If you really believe this story, you have been suckered.
    "He" is either a moron or is getting a good laugh out of your gullibility.
    Seriously.
     
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  7. privilege

    privilege Active Member

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    running 10w30 would do nothing negative to your connecting rods, except increase oil pressure, film, and cushion between them and the crank.
    it will definitely not damage your engine.
    it will definitely not decrease consumption, if consumption had reached a point of 1 quart every 1,000 miles.

    if the clearance on the con rods, and or crank bearings increased at the same time as running 10w30 , it was only a coincidence, and not causation.

    if you stopped running the engine in time (quickly!) there's a chance you could replace your rings and bearings, and still get another 100-200k miles of service from it.

    never run a knocking engine. always shut it down immediately and get it repaired before it makes windows into it's soul
     
  8. rjparker

    rjparker Senior Member

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    More likely it blew a head gasket and then hydrolocked.
     
  9. mr_guy_mann

    mr_guy_mann Senior Member

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    Using 10w30 oil in your engine by itself wouldn't have caused failure- something else happened. About the only "negative" things that would occur are taking a little longer to get oil to all moving parts on cold startup and a slight reduction in mpg due to more torque needed by the oil pump.

    Posted via the PriusChat mobile app.
     
  10. Fred_H

    Fred_H Misoversimplifier

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    @M67v , I hope we have convinced you that your problem cannot have been caused just by using 10W-30 oil.

    Once in a while, a spark plug can become loose or broken, even if it was properly torqued. That would be consistent with your symptoms, and is especially suspect because the plugs were recently worked on. Did you use a torque wrench? Was there much resistance when screwing in the spark plugs? Were the gasket seats clean?

    Misfire, knocking sounds, and fumes could also be caused by a leaky intake or exhaust manifold or manifold gasket.
     
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  11. M67v

    M67v Junior Member

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    I had a mechanic work on it at that time so I’m not sure
     
  12. M67v

    M67v Junior Member

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    i already got rid of it
     
  13. M67v

    M67v Junior Member

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    Man do whatever you want with your car but all I’m saying is I tried to warn you. Maybe the oil wasn’t the only issue but I don’t think it was a coincidence that the engine got messed up not long after I switched to a different oil.

    Plus, how do I know you’re not getting a laugh out of my “gullibility”? Again just don’t say I didn’t warn you.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    As several others have also tried to tell you............
    I am telling you absolutely, positively that just changing to a slightly thicker oil, and it is just ever so slightly thicker, is NOT the cause of your engine failure. It just is NOT.
    This is based on about 60 years now being a shade tree mechanic and auto enthusiast.
    You need to STOP spreading around that false information.
     
  15. PriusII&C

    PriusII&C Member

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    If the objective is to increase oil film thickness, it seems that the emphasis should be placed on the "warm" grade part, not the "cold" grade part, because the oil film thickness is much thicker at "cold" than at "warm" anyway. For example, go from 5w-30 to 5w-40. What is the logic to do the opposite, such as going from 5w-30 to 10w-30? Could someone enlighten me on the logic?

    In addition, does anybody have hard data to support the hypothesis of oil burning reduction by using a heavier oil? I want to know how effective it is.
     
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  16. frodoz737

    frodoz737 Top Wrench

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    This was your problem. The Mechanic was just an idiot.
     
  17. oldtechaa

    oldtechaa Active Member

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    Another issue with suspecting the oil is at fault in this scenario, which I don't believe anyone has mentioned, is that 10W-30 only increases the cold weight of the oil. This is an exceedingly small fraction of the oil's usage, only experienced on startup. Then when the oil is warmed up and it rises in weight it increases to 30 weight anyway, meaning that your engine can obviously handle 30 weight oil, so 10 weight is not an issue. I could maybe see switching to 20W-50 on an old engine, or 30W-60, if they even make such a thing, but increasing the cold weight of the oil will have little impact on the stress on your engine, but it will probably also have little impact on oil burning considering the small amount of time spent at that weight.
     
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  18. edthefox5

    edthefox5 Senior Member

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    Running 40 weight in my G2 for years. Its got an aluminum head & iron block.

    Not much difference between 5-30 & 10-30 except the 10 is a tiny bit thicker at cold temp who cares it's a 10 weight oil soon to be 30 weight oil. Soon as it heats up its a 30 weight oil.

    Many people run 40 weight oil in there g2 its the best thing you can do to mitigate oil loss.

    "Car was obliviously mistreated" pretty much explains it.
     
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  19. Fred_H

    Fred_H Misoversimplifier

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    Well, there you go. It's no secret that it's not uncommon for professional mechanics to make mistakes or not take the time to clean everything up and make sure everything is in perfect condition. I am not saying that that the mechanic did something wrong. I am just saying that you can by no means rule it out.

    You sold the Prius? Then the reason to continue this discussion would be to dispel the myth that only the single recommended oil viscosity is safe for the engine regardless of the operating conditions.

    Using the same logic, you shouldn't think it was a coincidence that the engine got messed up not long after the spark plugs and coils were replaced. Unless you were driving the car in extremely cold temperatures or if the motor oil was of inferior quality, then it definitely was a coincidence that the oil was also recently replaced with an oil of slightly thicker cold temperature viscosity. (The warm temperature viscosity was the same.)
     
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  20. M67v

    M67v Junior Member

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    How about, I’m giving my PERSONAL experience as to what happened me? Which btw is true information.

    Look my intentions is just I don’t want to see this happen to anything else, and you probably have good intentions as well but honestly people like you on forums just be getting way ahead of yourselves and you just need to tone it down for real.
     
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