Driving with diluted inverter coolant

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by tangerino, Apr 16, 2021.

  1. tangerino

    tangerino Junior Member

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    Hi all,

    My 2005 Prius finally hit 100k miles and I noticed the inverter coolant level was below the "low" mark. It was difficult to tell by how much but probably ~1cm. I think it's been at that level for at least a year or two looking at old photos I have of the engine bay.

    I used a $2 ethylene glycol coolant tester (5 floating balls) to check the coolant and got a reasonable reading, 4/5 floating.

    I was concerned about the level so I added about 1/2cup of distilled water to bring the level to just about full. Was this a bad idea? I figured it wouldn't affect the coolant quality much; given a capacity of 3qt, 0.5cup is about 4% extra, so maybe it brought the 50/50 coolant to 54/46. But now I used the coolant tester again and got only 1/5 floating balls. The level has held fine though, so it wasn't a leak that brought the level down either.

    Is the car still safe to drive with coolant diluted like this? I'm due for a coolant change soon anyway but don't want to burn out the inverter before I get a chance to do it.
    I'm in WA so it doesn't get very hot here, but would I be risking overheating my inverter when going on long uphills (or downhills for that matter)?
     
    #1 tangerino, Apr 16, 2021
    Last edited: Apr 16, 2021
  2. tangerino

    tangerino Junior Member

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    And would the inverter warn me with an engine code if it were over some temperature threshold, like a P0217 for engine temperature, or would it just keep going until burning itself out?

    It looks like I can measure the MG1 and MG2 inverter temperatures with my OBD2 to see if I'm approaching dangerous temperatures (>200C?). Apparently normal is just 20F above ambient temperatures (at least for Gen 3): Gen3 Inverter Coolant Temp? | PriusChat.

    EDIT: Looks like I would get a P0A93 code if there were a problem. Fortunately my coolant pump seems to work fine (see turbulence when on): Inverter Overheat | PriusChat
     
    #2 tangerino, Apr 16, 2021
    Last edited: Apr 16, 2021
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    1/2 cup water dilution does seem a drop in the bucket.

    FWIW, in the States Toyota says to do engine coolant at 10 years or 100k miles (whichever comes first), but delay inverter coolant to 15 years or 150k miles. Both are 5 years or 50k miles after first change.

    In your case though, maybe just do both; the inverter doesn’t take that much.

    In Canada Toyota recommends both circuits be done at 10 years or 160k kms (100k miles).
     
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  4. sam spade 2

    sam spade 2 Senior Member

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    1 cm below the mark when cold doesn't qualify to be concerned about.
    Adding that little amount of water isn't a concern either.
    Your added water probably isn't mixed up good yet.
    Give a few days and test it again.

    Regardless, it should be fine until winter sets in again.
     
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  5. edthefox5

    edthefox5 Senior Member

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    The coolant is 16 years old.
     
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah 6 years overdue for changing: Toyota recommends 100k miles or 10 years, whichever comes first.
     
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  7. tangerino

    tangerino Junior Member

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    Yikes I'll get those both changed then. They looked nice and clear pink though.

    I guess it's possible the engine coolant was done at 10years since it was on a city-fleet maintenance schedule (I'll have to dig up those records).

    For replacing the engine coolant I'd need Techstream to bleed the system, is that right? Or else use one of those special no-spill funnels? I read that for the inverter coolant I could turn the car on/off and let the inverter coolant pump run to get rid of any air bubbles.
     
  8. ChapmanF

    ChapmanF Senior Member

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    For the inverter loop, I believe Gen 2 has a bleed valve near the front of the inverter. You can pop a clear hose on the nipple of that valve, stick the other end back in the reservoir, and make the car ON (the two-button-pushes-without-brake-pedal state). The pump will run, you can open that bleeder and watch the fluid and bubbles travel through the clear hose. Generally you shake and squeeze the various hoses in the loop a bunch while you're doing that.

    For the engine bleeding procedure, I hope you have the repair manual procedure handy (or a good reliable transcript of it); it's a bit fiddly, what with the multiple pumps and the thermos and all, making it kind of hard to sum up in few words.
     
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  9. Fred_H

    Fred_H Misoversimplifier

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    Here's an illustration from the manual that I just happen to have handy:
     
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  10. edthefox5

    edthefox5 Senior Member

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    yep stupid easy. just make sure you open the right dump bolt the trans and inverter coolant dump bolts are right next to each other
    on the underside.

    The bleeder petcock is on very tight so grasp the petcock body with some water pumps then while holding the body open the petcock with some pliers. after hooking up the hose.

    Auto parts stores sell a product called Redline Water Wetter its a great product its used to improve car cooling systems. My car has had it in its inverter for 14 years over 3 changes. The circulation is so strong it looks like the coolant is boiling in the tank.
    I use wetter in all my cars.Never ever any cooling issues. Still on original ice water pump.

    Throw A bottle in the inverter and then fill the rest up with Toyota LLC. The inverter will love it.

     
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