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High mileage gen 2. Slightly thicker oil drops mileage

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Anthone, Jun 3, 2024.

  1. Anthone

    Anthone New Member

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    I was advised to use a 5w40 oil instead of a 5w30 as my prius has done 208k miles and burns a little oil.

    This seems to have dropped my mileage on a UK 5lt gallon, from ~65mpg to ~55mpg. ~£100 per 5k miles at our prices.

    At that rate it would be cheaper to burn oil or modify the thicker oil.

    I have looked at buying pure molybdenum disulphide powder to add. 1.5 microns. It is a friction modifier and that way I know exactly what I'm getting and how much I've added. ~2-3g per litre is what I was thinking.

    I also discovered tungsten disulphide at 0.6microns. Which is slippier still at slightly higher cost. Same dosage.

    Both cost much less than the extra fuel I burn at my current mpg.

    Or I could drop the oil, put 5w30 back in and keep it topped up. But that might increase engine wear?

    Thoughts?
     
  2. Tombukt2

    Tombukt2 Senior Member

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    Who cares even burning a little oil it'll be a long time until you do anything about it The car may fade off into Oblivion before you get to do anything about it for other reasons certainly not the oil problem these things the one NZ will almost run with no oil I am just kidding but I'm just saying it's a very stout little engine If you're burning oil like to the tune of a quart and say a thousand miles you don't even need to do oil changes anymore just about just keep adding oil the cheap stuff I mean the cheapest stuff no need to worry about high mileage engine oil or any of that nonsense. I've got one running just like this and it's probably going to go another 200,000 mi like this to put me at 650k or so a little oil burning not a problem for me at all I can't even see it It's not like it's coming out to tailpipe and smoke that's for sure and it's not leaking so I guess the burning is so minut you can't even see it we'll take it. I'm not going to be busting open any engines and whatnot for that.
     
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  3. ozmatt

    ozmatt Active Member

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    That mpg seems excessively different, I have swapped quite a few high k gen2 cars from w30 to w40 and noticed virtually no difference on the MFD, I mean maybe 4.8 or 4.9L/100 vs 5L/100

    gen2 will happily burn oil for hundreds of thousands of miles without any other Il effect, there is no EGR to block up & they don't blow head gaskets, keep adding oil until the smoke out tail pipe is embarrassing or it's costing you more in oil than fuel, ha! ..

    keep the old gen2 cars running as long as possible, they are legends

    Posted via the PriusChat mobile app.
     
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  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    It's good as a friction modifier, but it's also good at poisoning catalytic converters when it burns. You'd rob Peter of pennies to pay Paul pounds.

    Stick with plain 5W30 and enjoy burning it. After 200k miles, what wear are you trying to prevent exactly?
     
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  5. T1 Terry

    T1 Terry Active Member

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    The down side of burning oil is the carbon created blocks the catalytic converter honey comb matrix and certainly stuffs the 02 sensor. Try running an oil flush additive before you drop the oil next time and change the filter at the same time. Return to using the 5w30 oil and check if that helps the oil usage and the fuel economy returns.
    Just topping the oil up rather than changing it results in acids building up in the oil and bearing failure will be the death of the engine.

    My ex taxi Prius is off the road at the moment, the engine is still fine, a tad noisy, but with the high odometer reading, you'd expect that. I did suffer with a blocked CAT, but an after market AUD$100 unit sorted that problem. I did run a cleaning product that also contains graphite before again dropping the oil and filter @ 10,000 kms. The oil filter was heavier than usual and the oil was black and thick, the next 10,000km the oil stayed clean and the oil usage dropped, can't say if it was the cleaner or the graphite that made the difference, or both, no way of knowing really.
    Unfortunately, it seems something in the electric motor seems to have thrown in the towel, a shudder under load at low speed and the performance isn't what it was before, so it donated a set of disc pads and the new traction battery to my Silver '06 Prius that I resurrected after the battery fire and it's still going great and has 365,000km on the clock now.

    T1 Terry
     
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  6. BiomedO1

    BiomedO1 Senior Member

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    dumb question; what's preventing the powder additive from getting caught in the oil filter?
    How much oil burn are we talking about per oil change? What's your oil change interval?
    When you switched oil weight, did you also switch brands and move to a high mileage oil?
     
    #6 BiomedO1, Jun 4, 2024
    Last edited: Jun 4, 2024
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  7. Anthone

    Anthone New Member

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    Not dumb.

    0.6 microns should pass through the oil filter.

    I don't know. The car is new to me and had almost no oil on it. Maybe a litre. Still running like a sewing machine and no leaks...

    It will be 5000 miles.

    Almost certainly a diffent brand. Triple QX.

    Not specifically high mileage.
     
  8. Anthone

    Anthone New Member

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    Ah, good point.

    Would the titanium WS2 also poison the cat in the same way you're telling me the moly MoS2 would?
     
  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I'm the wrong kind of chemist to tell you.

    I would point out that the sulfur was the poisoning agent, and these are both sulfides but that's as far as I go.

    Here in the USA we see motor oils bearing MoS2, all labeled 'FOR USE IN DIESEL ENGINES' because that's the ideal destination: they need good lubrication and there's no catalyst to ruin.

    I used one successfully in a gasoline (petrol) -fueled Subaru without harming the catalysts. This was fairly common among enthusiasts of turbocharged Subarus, at least at that time.

    The MoS2 was very good news for our hot turbos, but if we ever detected signs of oil burning we had to act fast to save the cats.

    ...we weren't doing this on high mileage cars that routinely burnt oil.
     
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  10. Anthone

    Anthone New Member

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    That makes perfect sense, as does the fact they're both sulphide and that's the guilty culprit.

    Thank you for the good advice.

    I'm a bit sad I won't have super slippy engines parts and a personal record high mpg. The child scientist in me was going to enjoy the experiment.

    But better not to kill the cat.
    They don't all have nine lives.
     
  11. ebikeman

    ebikeman Junior Member

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    I was reading in my manual today and caught a page I didn't notice before. It says they burn most oil when using the re-gen feature.
    I'm posting about it later. Just thought I'd add this in when I saw this.
     
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  12. douglasjre

    douglasjre Senior Member

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    Check your oil pressure and let that be your decider and the report here so we all learn from it
     
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  13. Anthone

    Anthone New Member

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    How do I do that?
     
  14. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    As with many cars, you temporarily remove the oil pressure alarm sending unit and install a pressure gauge in its place. Take four readings: cold start idle rpm, cold high rpm, hot idle rpm, hot high rpm.

    Then you re-install the alarm sending unit and decide what to do from there. It really helps to have comparative numbers for the same type of engine. Anyone can tell you that the hot idle is the score that suffers the most on a worn out engine, but I couldn't tell you how low is too low.
     
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  15. Anthone

    Anthone New Member

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    Easier said than done.

    No idea where that is and don't have an oil pressure gauge.

    I was hoping you were going to tell me how to make the car display it
     
  16. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Wouldn't that be nice? But that's one of the things they had to leave out to hit a Toyota-worthy window sticker.

    The sensor in the car is a simple on/off switch that either trips the low pressure alarm or not. There is no proper sensor anywhere in there, so one must be added in order to get real readings.

    It would cost about an hour of labor for any mechanic to do this, if you're serious about taking readings.
     
  17. Anthone

    Anthone New Member

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    I'm a diy kind of guy. Have tools.

    It wasn't my idea but where is it and how much is a sensor?