Prius Prime engine oil change intervals

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by Laura-Ann, Oct 10, 2021.

  1. Laura-Ann

    Laura-Ann Junior Member

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    My 2 years of free maintenance from Toyota expired last July, so I am now going to be doing the engine oil and transaxle fluid changes myself. This has set me to thinking about the implications of owning a PHEV, regarding engine oil change intervals: How do you determine a reasonable engine oil change interval for a vehicle in which the odometer mileage can't be directly linked to the number of hours of engine run time? My last Toyota was a Yaris, and I changed the oil at 4,000 mile intervals. Since the average speed I drove was about 40 mph, that works out to an oil change about every 100 hours of run time. Probably twice as often as most people change oil, but we have really hot summer weather where I live, and fresh engine oil is pretty cheap considering the replacement cost of the engine it's protecting. But how do you figure out when a PHEV Prius has accumulated 100 hours of ICE run time, when the Prius ECU does not log PID #7F? (FYI: #7F is the OBDII PID that logs engine run time, and it's only required on commercial diesel truck engines in the US, so Toyota didn't include it in the Prius ECU). Someone who uses their car mostly for short hops of 30 miles or less is not using the ICE nearly as much as someone who is commuting 100 miles to work each day, and is thus not getting much EV time on external battery charges.

    I've come to the conclusion that the only easy way to track ICE run time on a Prius Prime or Rav4 Prime, since the car's ECU isn't tracking it or providing it in the OBDII data, is to keep track yourself of gasoline purchases, and equate gasoline consumption to ICE run time, based on the kind of driving you do. Since I rarely drive faster than 55 mph (fuel consumption in the Prius Prime rises sharply above this speed), and the car gets 65mpg at 55mph, that works out to 55/65=0.84 gallons per hour. Extrapolate this to 100 hours of run time = 84 gallons of gasoline consumed = 5,460 miles driven on the ICE at 65 mpg. By equating run time to gasoline consumed, you de-couple the odometer mileage from the ICE, and thus can forget about having to wonder how much of your driving was in EV mode vs ICE/Hybrid mode.

    I've driven my Prius Prime 19,191 miles since July 2, 2019 - that's 27 months, and I've used 153 gallons of gas in that time (and an unknown number of kilowatt-hours of external battery charges). My real-world fuel economy is thus 125 mpg. So if I've driven 8,529 miles per year on average, and burned 77 gallons of gas per year average, if I change the motor oil once a year I'll be right around my target of an oil change every 5,000 miles of ICE run time. I'll keep tracking gas purchases, and if I start making more road trips, to where I'm using the ICE more often and it looks prudent to change the engine oil more often than once a year, I'll at least have an idea of when the actual ICE run time is approaching 5,000 miles.

    As for changing the transaxle oil, that can be still be tied directly to the odometer, and the fluid changed at whatever mileage you feel comfortable with - 60,000, 40,000, 20,000 or whatever. If you live somewhere where the summer season daytime high temperatures exceed 90°F, I'd suggest changing transaxle fluid more often than the 60K factory recommendation, maybe 30K~40K. That transaxle is full of temperature-sensitive electronic parts - the two MG stators to be specific - and the transmission oil is the only thing keeping them from burning up.
     
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  2. Salamander_King

    Salamander_King Senior Member

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    Don't know about Rav4 Prime, but PP shows EV driving ratio on the Drive Monitor. If you never reset it, then the number corresponding to ODO is for the lifetime. The EV ratio includes the EV portion of the HV mode drive

    The photo below is from my 2017 PP. 60% EV ratio means 40% Engine on. So, for 36Kmiles ODO, 40% or 14.4Kmiles was on the engine. But, if I keep my Prime longer than 3 years, I will just follow the manual which says oil change 10K miles or 1 year whichever comes first.
    upload_2021-10-10_22-44-31.png

    I commented on the Gen4 thread, but Prius (PP or any other Prius family cars) has no transmission (or transaxle) fluid change recommendation interval. I changed my Gen3 at 30K, but for PP which I will not likely to keep longer than 3 years, I won't bother with it, unless I change my mind and decide to keep it for a long haul.
     
  3. Diemaster

    Diemaster Active Member

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    I'm just doing it the lazy way and going by the odometer. But since I only drive ~5,000 a year, it works out to the once a year I would have to anyway. I dont think it NEEDS to be changed yearly especially with EV driving and using the new synthetic oils, but $25 of oil is cheep insurance to cover more than $2500 engine / generator / traction battery / labor replacement costs.
     
  4. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I'd stick with the Toyota USA recommendation, at least for the duration of the power train warranty. I believe that's yearly or 10K miles, whichever comes first. Keep a lthorough log, and all supply receipts.

    One thing I do which maybe covers my butt better: purchase oil and filter through dealership parts department, where my car is registered. That way dealership has same receipts as me.

    FWIW, with Honda vehicles, which have a Maintenance Minder system, they recommend to at least change the oil yearly, regardless of what Maintenance Minder says, unless the vehicle's completely mothballed, I suppose.

    Maintenance Minder info
     
  5. bisco

    bisco cookie crumbler

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    you could get an oil analysis done
     
  6. Laura-Ann

    Laura-Ann Junior Member

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    Salamander King says: "but Prius (PP or any other Prius family cars) has no transmission (or transaxle) fluid change recommendation interval."

    I find this disturbing, because I've seen several YouTube videos of what the transmission fluid in a Prius transaxle can look like after 50~70K miles: so dark that it's almost black. I've talked to several professional mechanics at independent Toyota repair shops, and I've mostly been told that they change the fluid in their own Toyota hybrids at 30K intervals, mainly because of how hot it gets here in the summer months. If I do my first change at 20K, and the fluid is still nice and pink, I'll know that I was worried unnecessarily, and I'll do the next one at 60K. But if it comes out dark and gunky, I'll have maybe saved myself the cost of an eventual premature transmission replacement. Oil is cheap. A new MG2 stator is like $3500 for parts and labor. The risk of dirty oil in a Prius is that the dielectric properties of the oil can change as it gets dirty, and cause arcing or a short circuit in the stator windings if the oil becomes too electrically conductive due to carbon buildup or metal particles suspended in it.
     
  7. Salamander_King

    Salamander_King Senior Member

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    I agree with you completely, especially if you plan to keep your car for a long time. From what I have read, the fluid is dark even at very early transmission fluid change, but that does not mean it will not last for 100Kmiles or longer without changing. I for one had the WS ATF changed on my Gen3 at 30K miles and asked for the fluid sample. It was dark brown to black not transparent pink color. But Toyota's official recommendation has nothing on transmission fluid change. I have never had any car Toyota or otherwise that I had to have transmission work done. I have not yet read here any older Prius needing transmission repair. For my PP, knowing I will not keep the car longer than 3 years/3600 miles top, I am not going to worry about what is not required maintenance item. All I am going to do on my PP is routine maintenance recommended in the manual which is annual (or 10Kmiles) oil/filter changes. that will be it.
     
  8. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I did a transaxle fluid change at one year mark (around 16K kms), and it was noticeable darker than new fluid. Then, a second, and a third, each time at longer interval, and with each time there was less darkening of the fluid, to the point I think I'm done.

    Bottom line from my perspective: the first change can't happen too soon. but from there on the fluid is much more durable, might be more durable, purely judging from appearance.
     
    #8 Mendel Leisk, Oct 11, 2021
    Last edited: Oct 11, 2021
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  9. bisco

    bisco cookie crumbler

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    tranny is the most reliable prius part, but prime has a clutch. idk if that matters
     
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  10. BiomedO1

    BiomedO1 Junior Member

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    I experienced the same, on my 2012 Prius C. First ATF change was at 20K, it came out black cherry red - almost brown. The second change was at 75k, ATF was darker than new, but cleaner than the 20K mile change. The car was totaled at 92k.

    I plan on following the same procedure on this 2021 Prime; it's cheap insurance.

    BTW; lots of driving through the Sierra mountains in that Prius C; 8 years in the hot Sacramento summers.
     
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