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Excessive Fuel Dilution of Oil

Discussion in 'Gen 2 Prius Technical Discussion' started by ekpolk, Apr 4, 2007.

  1. ekpolk

    ekpolk What could possibly...

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    Well, I just got back my second UOA for my Prius (owned since last summer). I've already entered the data over at BITOG, so rather than retype, here's a link: Click here.

    To summarize, I logged 5800 miles on this fill of Pennzoil Platinum synthetic 5w-30, finishing the OCI with an 1800 mile vacation trip from Pensacola to Key West and back.

    What's alarming to me is the fuel dilution. More so since I drew this sample about 20 min after completing the vacation trip, when the engine should have boiled off a maximum amount of fuel and other aromatic contaminants. Yet the fuel is still almost 2%. It could well be 2-3x that in normal usage. Hot viscosity is down into the 20 wt range as a result.

    On the upside, while I've got dilution, clearly, I have no damage showing up yes, actually, quite the contrary.

    Here's the scary part: my oil analysis guy says he has seen multiple examples of Prii with substantial fuel dilution of the oil. Now, I have no way of knowing for sure, but this certainly could be a good reason to explain why, while almost all other contemporary Toyotas are being spec for xw-20 oil, the Prius has remained a 5w-30 car. If I had run a fill of 20 wt oil in this instance, I'd probably be approaching a 10 wt and have a crankcase full of something close to kerosene.

    I do realize that some here have run 20 wt oils without apparent damage. Has anyone else here seen excessive fuel in their oil on UOA?
     
  2. ScottY

    ScottY New Member

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    I've done two UOA's, once hot (engine on for more than 10 min), once... well... warm (engine was on maybe 5 min). The hot sample contained 1% fuel, while the warm sample contained 0.8%. What's the fuel amount in other normal gas engine UOA's? The vis @ 210F were 56.5 and 59.8, respectively. I use M1 5W-30 by the way.

    On the topic of sodium, dealer oil is suspected to contain high amount of sodium. The first UOA after I switch from dealer oil had 50ppm of sodium. The UOA after that, sodium level dropped to 4ppm.

    I don't use 20 weight oil, so I have no experience.
     
  3. Bill Merchant

    Bill Merchant absit invidia

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    Here's a question for you oil afficionados: Could the Atkinson cycle put more fuel in the oil than the Otto cycle? Does the Prius ICE rebreathe the fuel vapors? Where did the fuel go in the warm sample?
     
  4. ScottY

    ScottY New Member

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    maineprius947 compiled a spread sheet with all the UOA's posted on PC, http://priuschat.com/index.php?showtopic=27461

    From that, seems like couple of UOA's contain pretty high fuel amounts.

    Bill, I have no idea how to answer your question. :blink: I think only the engine experts would know. I guess taken the sample at different condition will be enough to produce the 0.2% difference? Just to be clear, the two samples were taken 9 months apart.
     
  5. iaowings

    iaowings New Member

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    Ok wow. I have no idea of exactly what was just said. I sort of get the point. You guys sound like medical personnel running and discussing labs on people. I am not knocking you guys in anyway at all to tell the truth I am farley impressed and feel I learned something from this post. Thanx.
     
  6. ScottY

    ScottY New Member

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    IAO, no worries if you don't understand. I started fresh when I have my Prius. This is my first new car out of college, and the first car that I actually take care of. If you want to learn more about used oil analysis (UOA), visit Blackstone Lab's page, http://www.blackstone-labs.com/gasoline_di...eport_expl.html. You'll get some basic idea what all these numbers mean.
     
  7. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(ekpolk @ Apr 4 2007, 09:08 PM) [snapback]418002[/snapback]</div>
    My first sample test indicated fuel dilution. Someone suggested that it might not have been run hot enough to evaporate it away. This was after 1000 miles of use of Penzoil 5W-30. I just sent in a sample of the same oil at 5000 miles. I'll see what the report on that is.

    Dave M.
     
  8. ekpolk

    ekpolk What could possibly...

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    <div class='quotetop'>QUOTE(dmckinstry @ Apr 5 2007, 12:40 AM) [snapback]418058[/snapback]</div>
    Dave:

    Two thoughts on this. First, I pulled this sample at the exact moment when fuel dilution should have been at its absolute lowest -- literally 20 minutes after my wife and I had finished driving from Key West to Pensacola (over 700 miles). Hours of doing ~80 on I-10 should have burned off all the fuel and any other volatile contaminants. This leads me to believe that my dilution is probably substantially higher in normal day-to-day driving. Second, my oil analysis guy (Terry Dyson, great guy, knows his stuff, highly recommended) says he's seen a pattern of this in other Prii. On the other hand, the wear metals pretty clearly indicate that I had not reached the point at which dilution compromised the oil sufficiently that it caused damage. My car is cert used, so I'm staying with 5k OCIs for now, but I think this result is a "wake up call" that those who are running longer should watch things carefully and be perhaps cautious about experimenting with xw-20 oils.

    Scott:

    My other cars, and many others I've seen reports from in the BITOG UOA forum, usually show zero or mere trace indications of fuel. It's usually considered an indicator of a problem of some sort (PCV problem, failed thermostat not allowing engine to reach op temp, etc).

    Bill:

    That's a tantalizing question. I've just installed CAN view v3 (couple nights ago). It has readouts for fuel flow and injector performance. I'll be watching those parameters to see if they lend any clues. Atkinson cycle operation might have something to do with it, but that will be hard to determine for sure.

    IAO:

    I invite you to join us at Bobistheoilguy.com. See the link I posted above. We are a somewhat obsessed bunch... Anyway, we have a used oil analysis subforum in which hundreds of results are posted (maybe thousands by now). You can casually peruse them and get an idea of what is good, bad, ugly, normal or abnormal, etc for given engine types. It's fun, and it's nice to KNOW how your engine is doing vs just changing oil and hoping you don't have any lingering problems you can see until it's too late.
     
  9. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(ekpolk @ Apr 5 2007, 03:32 AM) [snapback]418116[/snapback]</div>
    Thanks for that additional information.

    Dave M.
     
  10. dcoyne78

    dcoyne78 New Member

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    I also visit bitog from time to time (dcoyne78), what is the mileage on your Prius, would a stuck PCV cause fuel dilution? So far I haven't had a problem, but I am not paying for Terry Dyson's Analysis, maybe the Blackstone numbers that I have been getting are not correct. I don't add anything to my oil, I'll be posting a 10K result in about a week, so we'll see if I am still ok. I also plan to replace the PCV valve soon, though this may have nothing to do with fuel dilution. Terry has also recommended a Fram air filter for Honda's with fuel dilution problems, so if a Fram air filter is available for the Prius, it may be worth a try. I know Terry's advice is proprietary so you can't share Terry's tips for solving this problem with us without his permission. One indicator of fuel dilution is low flash point, so I will test this theory on my next oil change by using a Fram air filter, if available.

    Dennis
     
  11. ekpolk

    ekpolk What could possibly...

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    Dennis:

    Nice to see you over here too. I was wondering about the PCV, but thought that if it was significantly malfunctioning, shouldn't that generate an MIL light before too long? I really don't know, so if anyone else does, or know the threshold at which a bad PCV would trigger the MIL (if at all), please chime in. My MIL has (knock on wood) never come on, and my CAN View is showing no DTC codes at all.
     
  12. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(Bill Merchant @ Apr 5 2007, 12:42 AM) [snapback]418017[/snapback]</div>
    I don't know the answer to your question, but in thinking about it, the Prius engine does have high compression for a gas engine. Higher compression can increase the amount of blow by, as in diesel engines where you get a lot of soot in the oil. Just a thought.

    Tom
     
  13. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(maineprius947 @ Apr 5 2007, 06:55 AM) [snapback]418173[/snapback]</div>
    How does one do a flash point test, and what temperature would be considered low?

    Dave M.
     
  14. ekpolk

    ekpolk What could possibly...

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    <div class='quotetop'>QUOTE(dmckinstry @ Apr 5 2007, 07:26 PM) [snapback]418532[/snapback]</div>
    Dave:

    A measurement of flashpoint is included in most all used oil analysis reports. Fuel dilution will mess up flashpoint in a hurry. Normal values run in the mid-300s (F). If you hit my link (OP), you'll see that mine's all the way down to 260! OTOH, again, I'm still in "no harm, no foul" territory, but it's pretty obvious that the fuel is causing problems. The real question, I suppose, is when the trouble (elevated wear, deposits starting, etc) will begin.

    Gene
     
  15. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(ekpolk @ Apr 5 2007, 05:03 PM) [snapback]418552[/snapback]</div>
    Well, I'm waiting for the results of my last analysis yet. It was sent in about 10 days ago. I was mailed from Calfornia, rather Cheney, WA which is the usual starting point.

    Dave M.
     
  16. dcoyne78

    dcoyne78 New Member

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    Is it ok if I add your UOA to our database? I will wait to hear, also I will look for your first UOA on bitog to add that as well if it is ok.

    Dennis
     
  17. ekpolk

    ekpolk What could possibly...

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    <div class='quotetop'>QUOTE(maineprius947 @ Apr 9 2007, 07:46 AM) [snapback]420197[/snapback]</div>
    Absolutely yes, no problem. Same as to the first if you like.