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I think I've figured out why there's oil burning in Prius

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by JC91006, Aug 27, 2014.

  1. JC91006

    JC91006 Senior Member

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    I've thought for a while about why some Prius car's don't burn much oil and some burn lots of oil. Some owners claim they are meticulous are doing oil changes every 5000 miles and still get oil burning issues.

    I want the engine experts to ring in on my "theory". The reason I believe that oil burns is because of engine wear. How do engines start off being the same, end up being so different when they age? I believe it has to do with INITIAL START UP WEAR AND TEAR.

    As you all know when we first start our cars, it's in electric mode for about 10 seconds before the ICE kicks in. Some of us, myself included, will drive the car right away before the engine kicks in. By the time the engine kicks in, I could be doing 25 mph already. I think this is the reason that our engines wear, from having a 25 mph load on the engine when it first starts, no oil circulating. You do this repeatedly for 75k miles and you will start to see engine wearing and oil burning.

    I would think the people that don't have the oil burning issues don't start driving their cars right away. They most likely let the ICE engine kick in and circulate through the engine before they start driving. When there is no load on the engine, there is significantly less wear being done.

    What do you guys think?
     
  2. bisco

    bisco cookie crumbler

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    sounds like as good a theory as any. i have no idea, but i wonder if synthetic will reduce this in gen III?
     
  3. CBarr31

    CBarr31 Active Member

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    JC91006,

    It's a good theory and may apply to some instances of "The Burn" but there are so many different things that can be causing excess oil usage to attribute them all to one thing doesn't hold water, IMO. Ema for one seems to debunk this theory because I almost never drive before the engine starts because I am programming in customers to the GPS or moving crap around or something.

    Ema seems to support "striae" wearing down and not holding oil as well. This was mentioned by Rude person's mentioned in the "Low Oil Horror Story" thread you have replied in. I guess this is actually engine wear so supports your theory but isn't necessarily from cold starts.

    There is an interesting article in the ASME magazine this month called "Cold Start ... Dead Sensor" talking about how oil acts as a dielectric on cold starts and can take out sensitive engine components. The article is talking about jet engines I think, haven't had a chance to read it yet just skim, but it is also something to look at.

    Anyway my $0.02 is finding a primary root cause for oil burning will be engine specific and no single cause would be found. Sometimes rings, sometimes valves, sometimes wear, sometimes overfill, carbon buildup, etc... etc...

    Happy driving,
    Chris

    PS - I ordered some Liqui Moly and am going to give it a shot, LOL.
     
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  4. JC91006

    JC91006 Senior Member

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    Did you buy your car new and always waited til the engine kicked in before driving? My theory is for engines that started burning quite early in their life. I'm trying to figure out why some people (my 2010 with 65k miles) started burning oil at such a young age.
     
  5. valde3

    valde3 Senior Member

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    If hv-battery has enough charge and your gentle with gas pedal ICE doesn’t get any more wear than if you waited.
     
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  6. CBarr31

    CBarr31 Active Member

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    [/QUOTE]
    Did you buy your car new and always waited til the engine kicked in before driving? My theory is for engines that started burning quite early in their life. I'm trying to figure out why some people (my 2010 with 65k miles) started burning oil at such a young age.[/QUOTE]

    Yes, I bought Ema new in March 2006 and have almost always waited for the ICE to start before driving. As documented in other threads my oil burning has improved dramatically with the switch to pure E0 gas. It also never really got any worse after I started limiting her to 4,000 RPM and under by watching the scangauge.

    Chris
     
  7. Britprius

    Britprius Senior Member

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    I never let my engine start when I drive from home. Living near the top of a hill I drive "or roll" down in EV mode regening and when I get to the flatter section of road the engine starts when I reach 31 mph. The car uses no measurable oil between 10k mile changes, and is now at close to 110k miles.
    The car has only had 0w/20 synthetic oil since the first oil change. The first 50k miles were mostly fast motorway miles the rest mostly rural driving in the 50 to 60 mph range.
    I believe the engine warms quicker under load, and perhaps the lighter oil circulates more readily.

    John (Britprius)
     
    #7 Britprius, Aug 27, 2014
    Last edited: Aug 27, 2014
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  8. pmike

    pmike Member

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    I have a 3 mile commute and have found that I get better mpgs on both legs if I let the car warm up and go into ev (about 45 seconds) before proceeding. I have started doing the same for long trips also. I am in Florida so the warm ups are usually on 45 seconds.
     
    #8 pmike, Aug 27, 2014
    Last edited: Aug 27, 2014
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  9. Britprius

    Britprius Senior Member

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    I get about 3/4 of a mile free energy recovery from my downhill run. Some of this of course is used to assist the engine on the flat as it warms up. If I let the engine start and warm up before moving off the battery gets full before I reach the bottom of the hill, and is unable to accept the extra charge so wasting energy.
    Our temperatures in the UK are well bellow yours, but we also do not have the dreaded thermos tank so less coolant to warm up from a true cold start.

    John (Britprius)
     
  10. JC91006

    JC91006 Senior Member

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    Great John, just tossed that theory right out the door. Back to the drawing boards.

    Wait!! You use 0w-20, so the guys with 5w-30 have a case.

    On second thought, the Gen3 guys are already on 0w-20.....theory shot.
     
  11. pmike

    pmike Member

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    I am in Central Florida coast so the biggest "hill" is crossing the railroad tracks.
     
    #11 pmike, Aug 27, 2014
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  12. JC91006

    JC91006 Senior Member

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    Wouldn't the engine accelerate wear and tear if it's running at a faster RPM when it first starts? If I'm going 25mph vs 0 mph. Since the engine is dry, surely that short time frame x 75k miles would eventually do damage.
     
  13. frodoz737

    frodoz737 Top Wrench

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    This is another oil thread where people are going to disagree heavily as always, but here is my two cents. Fact - All motors need to have good oil pressure and initial warm up for expansion before you put a "load" on them. When researching whether or not to buy a Prius, I read the many "tricks" owners did to get the very best mpg...including driving right off after power up or achieving "Ready" mode. Statements condemning regular car drivers for wasting gas idling for any period of time after start-up were and still are common. My "opinion" is at minimum let the engine go through it's first warm up cycle and shut off before driving and don't just punch it right away to get on the freeway or what ever . My "opinion" also includes changing with suitable oil and filter sooner than the "minimum" recommended by any mfg and checking the level at every fill up to be aware of changes. My Prius now has over 75,000 mile and does not burn any measurable volume of oil and this has worked on all other vehicles I have owned. Discussing any other variables or arguments people wish to explore is fine, but this works for me...and I make a living as a mechanic. YMMV
     
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  14. wjtracy

    wjtracy Senior Member

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    I am also starting (at this late date) to warm up our Prius for a minute before driving. But my wife will never agree to this sort of thing, so its of questionable merit.

    In any case, I don't think our Gen2 ever gets up to 25 MPH before the ICE comes on. If Gen3 does, then maybe that could be a reason for Gen3's to have more wear. Seems like your comments JC are related to your Gen3 oil losses.

    I do not know what causes it (oil losses) but believe some have blamed crud/varnish build-up on the pistons/rings (whatever we got in there) so I assume not letting the used oil get too crappy may help, as well as a new oil filter. But I go about 7000k miles on synthetic oil before changing.
     
  15. JC91006

    JC91006 Senior Member

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    All my Prius cars burn oil, not just my Gen3. My daily driver is the 2006 and I'm pretty sure it gets to about 25 mph before the ice kicks on.
     
  16. alekska

    alekska Active Member

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    Your assumption of no oil circulating at startup is wrong. Engine is spinned by MG at 1000 rpm for a little while every time BEFORE any gas is injected in it. So everything is well-lubricated when the load on the engine starts.

    - Alex
     
  17. JC91006

    JC91006 Senior Member

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    If this is true, it sure is quiet at 1000 rpm
     
  18. john1701a

    john1701a Prius Guru

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    That was confirmed 14 years ago. We were told directly by Toyota itself how startup worked.

    The smaller of the two motor/generators is used to spin the engine up to idle speed and is kept there until oil-pressure is established.... then fuel & spark.

    That's dramatically less stressful on an engine than the usual spark & pray method, where it's spun to just a fraction of that speed for only a brief moment.
     
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  19. JC91006

    JC91006 Senior Member

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    shouldn't this make noise in the engine compartment?
     
  20. john1701a

    john1701a Prius Guru

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    It does, if you listen carefully.

    I've heard it in parking lots, where you have to look around because you don't initially see the HSD vehicle but know it's somewhere near by.

    The sound is subtle and the hood area insulated. But it is distinct, not like the rough noise all of us grew up with.
     
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