Refill ICE coolant loop through drain valve under thermos?

Discussion in 'Gen 2 Prius Technical Discussion' started by pasadena_commut, Jan 18, 2025 at 1:37 PM.

  1. pasadena_commut

    pasadena_commut Senior Member

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    Typically one drains the Prius ICE coolant loop through the drain valve under the thermos, with the car tilted with the passenger side raised. Then it is filled at the radiator cap. I was wondering the other day what would happen if it was refilled through the drain valve, essentially reversing the drain procedure. This would mean putting a clean tube onto that outlet, attaching a hose clamp (so that the tube doesn't fall off) and then pouring it into a funnel at the other end of the tube from a level higher than the radiator cap.

    Anybody ever tried it? I'm wondering if filling from the bottom might result in fewer problems with stuck air bubbles. Or maybe it would be worse and it couldn't get past the thermos?
     
  2. Tombukt2

    Tombukt2 Senior Member

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    Why couldn't I bus put the rated amount of cooling in a big container put an air hose to that clamp up like you suggested and fix myself to the container that I have the coolant in and push it in with air not push through it with the air just push it out of the vessel gently up through the drain port you're talking about and then when it's empty then it comes out the cap or something close off that fitting and remove my clamp but if you're going to do all that isn't it cheap to buy that little device that lets you dump the whole amount of cooling in the radiator like all at once especially if you're going to be doing this any kind of regularly.
     
  3. pasadena_commut

    pasadena_commut Senior Member

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    People use Airlift devices from the radiator neck, which is sort of the opposite of what you describe (vacuum pulls coolant in, rather than pushing it in.) Really shouldn't need to force it in with compressed air, gravity will work fine. Just make the elevation of the entry point for the fill hose equal to the radiator neck and pour it into the tube through a funnel. Water in a filled tube will always rise to the same level at both ends. However, that isn't the same thing as saying that pouring water into a complex tube will necessarily fill it completely when the two ends are at the same level. If the tube had some inverted "U" shape passages, and the fluid went in slowly enough it could pour over the "crest" and leave a trapped air pocket at the top of each of those passages. So maybe it needs to go in faster, but compressed air isn't needed, just a greater elevation on the entry point of the tube. At the other extreme, if it was going in really fast there might be foaming or cavitation, both of which would be counter productive.
     
  4. Tombukt2

    Tombukt2 Senior Member

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    Yeah that's a cool thing all that but won't that take a while even if I lift the funnel and hose you know up to roof height of the car no problem I could even do it with a bucket that'll hold the exact amount of coolant that I need to get in the system which is whatever the manual says and then you could just leave it there with the cap off and go do something else and come back and when you come back you're coolant should be close to the filler neck top and your bucket should be empty and you haven't had to stand there or buy the tool.
     
  5. Tombukt2

    Tombukt2 Senior Member

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    But now that we're talking about this those of you with generation 2s that look or don't whatever. When you open your radiator cap on a morning or whatever before the cars ever been started it's been off for 8 hours If you remove the cap from this car under this situation and look down at the filler neck with the cap in your hand do you see coolant in the vertical part of the filler neck it's about 4 in long yes or no? If you squeeze the hose over to the right while you're standing in front of the car the fat radiator hose coming from the cylinder head if you squeeze that hose all the way down while looking in the vertical part of the filler neck do you see water make it to the vertical part of the filler neck when you squeeze the hose yes or no? My car undoing the radiator cap under these conditions I see no coolant in the filler neck If I squeeze my far right radiator hose it was just talked about I can hear the coolant in the radiator moving at the filler neck but can't see it. It will take a 24 oz Coke bottle of water or coolant for me to get the coolant to the top of the filler neck like it is in my Corolla almost ready to dump in the hole that goes to the reservoir. I get no heat until I fill up that radiator until I can get it to stand at the top of the filler neck that usually takes 24 oz of whatever liquid I'm using and I have to add it slowly out of a Coke bottle that's what I use to check my measurement I don't have a beaker close by. Until I get that coolant standing at the top of the filler neck I will have no heat I don't care if I drive 20 minutes or 2 hours and during that time that the coolant is not been filled up to the top of the filler neck every two or three minutes my red triangle comes on and the turtle or the car in the MFD is red with a thermometer and then by the time I look back up at the MFD and the dash the triangle and the turtle are back to green with no problem reported this will go on while I'm driving down the road I don't think this is a damper problem or any of that this is something to do with the coolant not staying level and I can't find a leak anywhere even into the cylinders I think what's happening is when I start the car in the morning the hoses get real hard and it tries to blow off coolant into my almost full reservoir which slightly overfills and comes out to overflow tube and drops on the underpan under the radiator and I'm looking for a leak but it's not leaking. I tried another cap from a running car that's driven every day and it does the same thing and my old cat from this car is on the other car running just fine daily. After this 20 minutes of running the bottom hose is hot on the thermostat housing side of the equation and starting to run up to the radiator The other hose coming from the head is also reasonably warm and as hard as the basketball The hose coming from the bypass at the top of the thermostat housing that goes all the way to the electric motor in between the brake pieces is running and it is not very warm not as warm as the other two main radiator hoses and I think that's where my heat is coming from and of course it's almost nothing and today it's 46°. So when it was 22 you can imagine. Is it possible that it's 390,000 mi my mechanical water pump impeller has literally worn off of its shaft never seen such a thing in 40 years but I guess it could be possible. I do know those electric pumps are pulling water around the system even when the car sitting there not running. Even with a call for heat the car will just shut off sitting in the driveway and be blowing cold air out the vent and I don't think it's a damper door after fooling with it for a few minutes and getting it real full of coolant all of a sudden the magically the heat will start coming through the system about like it's supposed to this is after the car's been running for 25 plus minutes and I've been cracking the radiator letting the pressure off over to the reservoir and then noticing I can't see any coolant and can barely hear it when squeezing the far right hose so I add more cooler and fill it up but I'm just wondering if everybody else's car this water is standing at the top of the neck or not?
     
  6. pasadena_commut

    pasadena_commut Senior Member

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    Water at neck in morning. Definitely not as cold overnight as yours might be though, it only gets down to 41F or so, and I don't know exactly what the thermal contraction would do overall. I suggest every morning filling the overflow tank to a mark at the center (there is no mark there, make one with a sharpie) and then at the filler neck up to and just over the outlet hole to the overflow. Drive normally but do use the heat at least a little each day. Keep an eye on it. Always park in exactly the same place so tilt will play no role. If it is just air in the system it will work its way out over time and the fluid levels should stabilize. If it keeps losing coolant the car may have an issue, although it could just be a bad radiator cap.

    Inspect the hose from the radiator neck to the overflow tank. If it had a tiny hole the car might be able to push coolant into the overflow but not be able to draw it back up into the radiator after parking.