Refill engine coolant, without trapped air. (unique method) Gen 2

Discussion in 'Gen 2 Prius Main Forum' started by Albert Barbuto, Oct 29, 2025 at 11:05 AM.

  1. Albert Barbuto

    Albert Barbuto Member

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    It was time to do my first coolant change. I read a lot of information here,(Prius Chat) and realized that trapped air can be a real time waster to remedy. The use of an air-lift tool is the solution to a carefree job. I've never needed such tool for previous vehicles, so I was without. What to do? I was thinking about this for a couple of days, before the light bulb moment arrived. Fill the coolant from the bottom up! The air should stay on top of the new fluid, and exit out the opened radiator cap. Time to try... If successful, I would share this method...


    (1) Drain all fluid out of the thermos bottle petcock, making sure to have the passenger side jacked up some, as this will allow more fluid to drain. Be patient, as it takes a while for all six quarts to empty. Now leave the petcock open.

    (2) Now you will need a S hook, or something to hold a jug to the hood latch. A long piece of plastic tubing is needed. ( 7' long x 5/16"(8mm) inside diameter) Test fit the tubing to the petcock before proceeding. Warming the tubing with heat will soften the plastic, if needed to expand and fit properly.

    (3) A hole needs to be made in the bottom of the jug. I used a tapered shank to make the proper diameter hole. Go a little at a time with your tool, test fitting the plastic tubing. You want a nice tight press fit.

    (4) Hang the jug from the hood latch. A funnel will allow the new coolant to pour into this container. Block the end of the tubing with your thumb, and fill the jug, or hold the end higher than the funnel, then seal the end with your thumb. Now bleed all air out of the tubing before attaching to the petcock.

    (5) The new coolant will fill much faster than it drained, due to the height of the jug. Do not let this jug run dry, as you will have to re-bleed the plastic tubing, to remove the air that is now in it.

    (6) After six quarts have been added, you will see fluid cresting the radiator cap. Close the thermos petcock. Remove the jug and plastic tubing. Keep the passenger side jacked up slightly, from step #1.

    (7) Run the thermos pump with a test meter, or paper clip, and listen. The difference in sound between air/no air in the system is huge. I did four 5 second runs. There was a little air.

    (8) Shove a funnel, or something that fits tight in the radiator cap location. Squeeze the large diameter radiator hose under the radiator cap many times, and see if any air bubbles come out. When satisfied, start the engine, place car in neutral, and let the engine run for about ten minutes. Make sure to set the parking brake, along with wheel chocks. The fluid level in the funnel will rise as the fluid warms and expands. Shut off the car, and let things cool. Now remove the funnel, and attach the radiator cap. You are finished... :)


    Note: Two days of driving and all is normal. I monitored coolant temps with Torque Pro, just to be be safe. IMG_2346.JPG
     

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    #1 Albert Barbuto, Oct 29, 2025 at 11:05 AM
  2. Tombukt2

    Tombukt2 Senior Member

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    But ya had to rig all that up . You can drop almost all in quickly . It's the last two quarts at most are the issue . Pour slooowly and have other things to do . Walk by the offending car every five min top off . Until finally it doesn't move in 5 minutes then you're full cap off top of jug and go heat on hi . Then turn heat down or off . Probably not revisiting this for a very long time afterwards unless s leak doh.
     
    #2 Tombukt2, Oct 29, 2025 at 11:56 AM
  3. pasadena_commut

    pasadena_commut Senior Member

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    Never tried it but did propose it:

    Refill ICE coolant loop through drain valve under thermos? | PriusChat

    Sounds like it worked well. Thanks for being first penguin off the ice and into the water.

    One comment though, I wouldn't hang anything heavy on the hood like that. The aluminum hood is pretty flimsy and it is just held up by a not particularly stout support - on only one side. It might warp, or it could fall down. Safer I think to hang the coolant from a tree branch, under a ladder, from an engine hoist hook, or basically anything that is handy and sturdy.
     
    #3 pasadena_commut, Oct 30, 2025 at 3:07 PM
  4. pasadena_commut

    pasadena_commut Senior Member

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    Three more minor points:

    1. When the fill starts it is OK if there is a continuous air bubble from the valve back up into the tube, as long as there is a solid column of coolant above that. When the valve opens that air will be pushed into ... more air, so it is harmless.

    2. It would probably be a good idea to fill slowly until the thermos is full, or at least mostly so. If the fluid enters so fast that it makes a fountain that will mix air also in the thermos into the coolant. It might be possible to tell if this is happening by listening to the side of the thermos as the coolant goes in.

    3. Good idea to run the heat on full for a while when filling this (or any) cooling system. Heater cores are a notorious location for air to get trapped, and in the worst case it will prevent coolant from moving through the core at all.
     
    #4 pasadena_commut, Oct 30, 2025 at 4:41 PM
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