Poor heat management of MG1 / MG2

Discussion in 'Gen 3 Prius Technical Discussion' started by ThatDudeOrion, May 9, 2019.

  1. ThatDudeOrion

    ThatDudeOrion Member

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    So I've finally got enough instrumentation to pass a somewhat informed snap judgement on why the MG windings are subject to burning out and failing....

    It's my assertion that the inverter / transaxle coolant loop and transaxle oil bath lubrication of the eCVT/differential do a piss poor job of cooling the MGs.

    I'm seeing MG temps 80-100*F higher than the inverter coolant temps
    AND
    I'm seeing MG temps 50-60*F higher than the transaxle fluid as measured by probe in the drain plug

    Both of these data points to me indicate that Toyota's design for cooling the MGs is not very efficient at pulling heat out of them

    please ignore the messy wiring in the pics below, this isn't in it's final form.

    temps were in the mid 50's F this morning and I still haven't reinstalled the lower engine cover, if anything I expect to see higher temps overall when I do, but I expect the deltas will still be similar.

    Now for the real question, is this actually a problem? well, on our family summer road trips loaded up with people and cargo and the yakima skybox, etc. I can easily see MG temps over 200*F, which is not good, and I feel like with some more efficient method of transferring heat away from the MGs we could further reduce some of the most likely potential failure points (MGs and Inverters) on the Gen3 platform, which is IMO quite a reliable platform already.

    Thoughts?

    [​IMG]
    [​IMG]
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  2. bisco

    bisco cookie crumbler

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    you're probably right. for normal driving, and vacation road trips, the cooling is probably sufficient. but if you're doing a lot of heavily loaded road trips in warm areas with a lot of hill climbing, an extra cooler would probably make sense.
    we see so few bad trannies though, it wouldn't be worth it unless you're going to keep the car for hundreds of thousands of miles.
     
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  3. Grit

    Grit Senior Member

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    Great post. I’ve been over conscious about Temp of mg1. During winters, it stays below 140 f after an hour of highway driving and now the outside temp is around 90F, mg1 goes up to 170F on same commute just myself and no passenger. When driven on hwy about 3 hours, mg1 can reach nearly 200F during the summer. Mg2 is typically 10-15 F cooler than mg1 on mine, hybrid assistant app monitor this data.
     
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  4. bisco

    bisco cookie crumbler

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    let me add towing as another caveat
     
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  5. ThatDudeOrion

    ThatDudeOrion Member

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    So I've actually been thinking about this for a while and in light of this new data, I'm not quite sure what to do....Before when I was just watching MG temps, I just assumed that the atf was gonna be really hot and had planned to install a gear oil pump and feed an air/oil cooler from the transaxle drain and back into the fill port. But with the atf oil temps being so low (and apparently not carrying much heat away from the MGs anyways) I'm not sure how effective that would be (Air-oil coolers get less efficient the closer the oil temp is to the air temp, right?) I actually already got the gear oil pump and some fittings but I didn't buy the cooler or the hoses yet.

    As far as the longevity, question, my theory is that some of the highest mileage examples of Prii are used in taxi/ride-share type situations, and based on my testing its the sustained high speed that really puts the heat into the MGs, not the city driving. My driving habits are precisely the kind that really get these things hot, so I reason I stand to benefit more than the average Prius owner, IF there really is any benefit to getting the MGs to run cooler.
     
  6. bisco

    bisco cookie crumbler

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    i'm no expert. google around, i think i've seen mention of coolers added, but idk the specific driving situations, or how well they work.
     
  7. mjoo

    mjoo Senior Member

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    If you have the means, an external cooler, pump and lines will also add volume to the trans sump. This alone should help keep temps down. You could also filter the oil - that will also add fluid capacity.

    IDK how much that will help MG1 or 2.

    FWIW, I once added a bypass filter across a transmission cooler. This made a failure-prone automatic transmission shift like silk and the fluid always had a cherry red color. Of course, an eCVT on the Prius doesn't shift...
     
  8. ThatDudeOrion

    ThatDudeOrion Member

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    yep a filter was always part of the plan, whether I do the cooler or not, which is why i felt ok buying the pump and stuff first.
     
  9. TMR-JWAP

    TMR-JWAP Senior Member

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    One question to consider is whether adding all that additional equipment to the (very well sealed) transaxle fluid system outweighs the risk of an accidental leak draining it undetected.
     
  10. ThatDudeOrion

    ThatDudeOrion Member

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    This is true indeed, the added complexity would introduce some additional failure points in terms of fittings, lines, oil cooler core, etc. but i would almost feel better if I tried something and it cost me a transaxle versus doing nothing and have the MG windings short out or something...I know that's a bit of a false dichotomy but I think you can get my idea.
     
  11. edthefox5

    edthefox5 Senior Member

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    The atf has nothing to do with cooling the mg's really that's the inverter coolants job and it does it well. if Toyota was expecting the atf to do cooling it would have installed a cooler. But they do not. Ever see a cooler on a manual trans? If your seeing high temps it probably has the original trans fluid and original inverter coolant.

    Fresh inverter coolant will significantly lower trans temp.

    Trans failures on a the G2/G3 platform are very low almost non existent based on what we see here and winding blow out if it even occurs is caused by over current through the mg winding's not heat related. Over current of the winding's is easy to do overload the car with people and cargo go up a large Mountain with low hybrid battery charge and when the car gets sluggish going up the hill floor it to maintain expected power like it's a magic car. Want to kill an electric motor high load it with low power. The lower the voltage the higher the current.

    That going up the hill fast with low power scenario has left many a g2 owner on the side of the road with an overheated inverter. The g3 has a much better power design with higher powered mg's so more power with less consumption but that scenario will still flog a g3 if the hybrid battery is getting tired.

    So as far as an auxiliary cooler you will get much better results reducing the inverter coolant temp than the atf but again Toyota already realized the mistake they made on the G2 and improved Inverter cooling on the G3 by making the inverter radiator completely separate from the ice rad reducing ice heat soak and reducing invert coolant temp. Great design.

    You probably still have the original fluids in the car. If you going to be fanatical be fanatical about maintenance. Put some high performance trans fluid and engine oil and coolant in the car
    and it will last forever.
     
    #11 edthefox5, May 10, 2019
    Last edited: May 10, 2019
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  12. ThatDudeOrion

    ThatDudeOrion Member

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    I appreciate your feedback but your assumptions about the fluids aren't quite correct in my case at least. ICE and Inverter coolants were changed 11 months and 30k miles ago with fresh Toyo SLLC and a surfactant additive to improve heat transfer. Trans fluid was just changed when I installed the temp probe at 136k and has been changed at 30k, 68k, 106k, been using MaxLife ATF since the first change at 30k.

    I have actually seen coolers on manual transmissions, and spray bars, etc. now on stock builds its less common, but I do believe the TR-6060 in the ZL1 Camaros has a cooler from the factory, for example.

    I agree with you that the inverter coolant coolant circuit does a great job of cooling the inverter as it stays mostly just above ambient in my recent memory. However, I don't see that it pulls much heat out of the MGs, and with it sitting somewhat close to ambient temps, I think you'd be hard pressed to get the Inverter Coolant temp down much more, and even if you did, I don't think it would lower MG temps that much, based on the deltas I'm seeing between inverter coolant and MG temps.

    Based on my research, these cars have basically 3 main weak points, that have been proven out thus far, and even those numbers are low, as you indicate, but for that 1 person who loses thousands of $$ on a blown headgasket, overcooked inverter, or MG winding blowout, the failure occurrence percentages across the population of Prii doesn't mean much to that person, when their sample has a 100% failure rate. That's what I'm trying to prevent. The line of thinking being: maybe the MG windings won't be as prone to blow out during a momentary over current situation if I'm not running MG temps of 200+ when the overcurrent occurs? maybe circulating, filtering, and cooling the transaxle fluid would help cool the MGs and be a means to that end.
     
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  13. edthefox5

    edthefox5 Senior Member

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    I disagree as the atf is really no wheres near the windings. They are basically encapsulated by the metal cooling channels of the inverter fluid that circulates very closely against the windings. But keep this in mind if there was an issue I am sure Toyota would have addressed it in the search of zero emissions, mileage, and longevity. They added the separate inverter rad and improved the mg's power. The achilles heel of the G2.

    Cooling the atf will do nothing to fix the boogeyman that you perceive. I would be more concerned with the EGR issues it has.
    Designing a atf heat exchange system on a G3 will be quite a feat. There's no room anywhere to install a exchanger/radiator and no ports to tap. And if you add say 4 more quarts of atf with a exchange system who's to say the stock pump in the trans can handle that? Fluid dynamics are a very tricky thing.

    And the winding's are not prone to blow out. You really have to work on that on a G2 as very very few have failed and have not seen any on the G3 so far.
     
  14. ChapmanF

    ChapmanF Senior Member

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    You've written that in much the same way a person would write something that was quite certain, but I don't understand why, as, if you were to look it up, you would find the opposite.

    Our Gen 3 (P410) transaxle uses the circulation of oil to cool the windings, thrown up by the gears into "catch tanks" formed into the inside of the housing, from which it drains down over the motor windings:

    earl.png

    (Sano, Shinya & Yashiro, Takahisa & Takizawa, Keiji & Mizutani, Tatsuhiko. (2016). Development of New Motor for Compact-Class Hybrid Vehicles. World Electric Vehicle Journal. 8. 443-449. 10.3390/wevj8020443).

    You can also see that in Prof. Kelly's P410 Deep Dive video at around 9:45.

    The closest the SLLC inverter-system coolant ever gets to any of that is some water-jacket passages cast into the outside of the transaxle case on the bottom and low front, where it carries away the heat ... from the oil ... through the aluminum case. The low front water-jacket cover plate is highlighted in green here:

    sllc.png

    Prof. Kelly points out another interesting thing: the MG2 end of the transaxle also has some water-jacket passages cast into the case, but completely unused in the liftback (highlighted here in purple). The Prius v uses the same transaxle, but it does have a water jacket no. 3 cover installed there, with its own pair of hose nipples, to do an even better job of transferring oil heat into the coolant.

    That suggests that anybody who really wanted to cool the oil better in a Gen 3 liftback would have a pretty easy way to arrange that; just buy the water jacket 3 cover, ten bolts and some 00826-00100 sealant, an extra bit of hose and a couple clamps, and enough extra coolant to fill up the added space, and there you'd have it, a liftback with a v's oil cooling capacity.
     
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  15. Grit

    Grit Senior Member

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    This was my commute on the way back, only couple of +/- 30 ft elevation change. Ambient outdoor temp was 90 F against 15 mph front head wind, 1hr 15min drive. I've done a couple of 200F & hotter MG1 & 2 temps driving 3 hours straight. I'll try redline D6 for atf next time and compare temps to toyota WS which is currently in.

    I did get avg 61 mpg for this trip w/o wipers and everything in the back taken out minus spare tire + scissor jack tools on 1/5 tank of fuel

    IMG_2056.JPG
     
    #15 Grit, May 10, 2019
    Last edited: May 11, 2019
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  16. TMR-JWAP

    TMR-JWAP Senior Member

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    Dang Chap,

    Now THAT is a great bit of info. That post alone could be the answer the OP is looking for.

    How many times has it been discussed on this site about whether to use WS fluid or something else. The replies are always passionate about the properties of WS not affecting the windings insulation coating and why many people will not EVER try anything else just for that reason. (personally, I'm sticking with WS, as I have about 14 quart bottles still in the garage from when I ordered it).
     
    #16 TMR-JWAP, May 10, 2019
    Last edited: May 10, 2019
  17. Avi's Advanced Automotive

    Avi's Advanced Automotive Independent hybrid repair shop

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    Can we please get the efficiency of the likely salt corroded inverter radiator compared to a brand new OE one?

    Posted via the PriusChat mobile app.
     
  18. ASRDogman

    ASRDogman Senior Member

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    There is no advantage to using any other fluid. The cost difference is pennies per quart.
    So WHY take the chance?
     
  19. Maarten28

    Maarten28 Active Member

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    MG temp will go up to 175 F even in 35-50 F outside conditions with gentle use. Let alone when it's 90 F outside. So back to your question: is this a problem? Why do you think it is?
     
  20. ThatDudeOrion

    ThatDudeOrion Member

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    I value your concern, but that's not what this thread is about.
     
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