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      03-19-2020, 07:49 PM   #1
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BMW F10 535i Coolant Flush DIY

After countless research on the topic with not much to show, I decided to pull the trigger and get this DIY done. I've got to say, after doing it through this method I can finally say that I got 100% of my old antifreeze out of the system. The reason I can confirm this is because whoever had the car before me put green coolant! Which we all know is a big no no.

USEFUL INFO: The N55 model engine uses 10 liters of coolant.

Furthermore, the tools you will need;

- [ ] Common sense (very vital here)
- [ ] A hose that is long enough to reach the vent hose all the way to your designated bucket
- [ ] 6 or 7 gallons of distilled water
- [ ] 2 gallons of OEM BMW non-diluted antifreeze
- [ ] A bucket(s)
- [ ] A couple of rags or towels

Essentially how the cooling system works is that it is circulated (obviously). The vent hose that connects to the reservoir is basically the return line in this case. The coolant passes through the entire system and returns to the reservoir through this single hose.


1. Release the vent hose from the coolant reservoir by prying the metal clip up with a small flathead. Then remove the hose by gently pressing it off the nipple of the reservoir.
2. Now get your hose, preferably a clear one to monitor the fluid coming out, and find a way to get the vent hose and the hose you're using to connect securely so that coolant doesn't leak out. The best way to do this is to have a hose with a wider diameter than the vent hose. Mine wasn't larger in diameter so I used tape and wrapped it in a microfiber towel to control any leaks. This worked well too.
3. With the cap off the reservoir, get in the car and turn the heat to max with the lowest fan speed. Also turn off The AUTO, AC, and other functions.
4. Start the car.
5. While the car is running you want to make sure the reservoir doesn't run empty and keep it filled with distilled water at all times
6. Monitor the fluid coming out of the hose. You will know that all of the old coolant is gone when the fluid in the hose runs clear.
7. With the car still on and running fill the car with the BMW coolant. You don't need to dilute it because the system is full of distilled water, this mixing with it in the system. My logic was that since the car uses 10 liters of coolant, and I filled the car with distilled water entirely, it's safe to say I would need to put in 5 liters of BMW coolant. If you feel that this method is faulty, just monitor the fluid that comes and make sure the mix is how you like it.
8. By the end of this, you should see the blue BMW coolant mix coming out. At this point you can shut the car off and insert the vent hose back into the reservoir tank.
9. This step isn't necessary in my opinion, but just to make sure there are no air pockets in the system, I run the BMW coolant bleed procedure which is basically having the car in accessory mode and holding down the gas pedal for approximately 10 seconds. You know it's working when the vent hose has coolant coming out of it. The reason I say this isn't really necessary is because you never really introduce any air into the cooling system like a typical fluid drain and refill situation would. As long as you keep the coolant reservoir filled you should be fine and dandy.

With that said, always be care not to overheat your engine when doing this. If it does, something is wrong. Yours shouldn't overheat in this procedure as long as it is filled with liquid. That is your priority.
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      03-19-2020, 07:50 PM   #2
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The picture above is to help clarify what I am talking about when I refer to the vent hose. This is the only thing you need to unclip.
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      03-19-2020, 11:18 PM   #3
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You should put the vent hose back when you've added 5 liters of antifreeze, don't wait for it to turn blue. Might want to make that more clear in the post. Your theory sounds correct to me though. It only works if you do this via the vent line though. My reasoning:

The vent is the return, so that means between the expansion tank and the return port, there's 10 liters of capacity. If you have 10 liters of distilled, and follow it with 5 liters of coolant, it'll flush out 5 liters of water, leaving you with close to 50/50.

One other thing, you absolutely can introduce air into the system even with this method. Turbulence of the coolant as you pour it in will likely cause a small but noticeable amount of air in. Always run the bleed procedure and top off with 50/50.
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      03-19-2020, 11:23 PM   #4
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Thank you for the constructive criticism. I changed it once I saw blue because I wanted to make sure coolant was in the entire system. Maybe my mixes are a bit off but at the end of the day it works. Bubbles also won't be introduced because of the system running constantly when the car is on thus bleeding it in the process. I don't know how you had that assumption. The whole process takes about 30 to 40 minutes and by that time with the car running it should be bled through. Pouring into the expansion tank may create bubbles I guess but those rise to the top as far as I am concerned.
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      03-20-2020, 12:55 AM   #5
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Quote:
Originally Posted by David_Vasha View Post
Thank you for the constructive criticism. I changed it once I saw blue because I wanted to make sure coolant was in the entire system. Maybe my mixes are a bit off but at the end of the day it works. Bubbles also won't be introduced because of the system running constantly when the car is on thus bleeding it in the process. I don't know how you had that assumption. The whole process takes about 30 to 40 minutes and by that time with the car running it should be bled through. Pouring into the expansion tank may create bubbles I guess but those rise to the top as far as I am concerned.
Sorry, I don't quote follow the logic here. To make sure coolant was in the entire system? As in, you're checking for leaks? This doesn't seem like a particularly good way of checking for leaks.

You misunderstood me, I'm not saying bubbles are going to be introduced by running the car. It's going to be introduced by pouring antifreeze into the expansion tank. Sure, most of the bubbles will probably rise to the top, but it's not like the bleed procedure is hard to do or something, so why risk it? It's still best practice to bleed the system any time you touch the coolant system.
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      03-20-2020, 06:33 AM   #6
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I like that common sense is on the list of required items

A weakness that I see in this process is the fluid in the radiator loop. The coolant system isn't a single loop, there are branches all over the place and one of these is the entire radiator. The thermostat needs to be open to ensure you've got proper flow here.

With every inline 6 BMW I've worked on, (M52, M52TU, M54, N52, N55) I have found that even in the summer heat when it's just idling and I have the hood up it sheds enough heat to the environment that the thermostat doesn't even necessarily open. (stop and go traffic in the blazing sun with the AC on is a different environment than idling in the shade in my garage with everything off and the hood open). On the N series engines with electric water pump, if the weather is cool the pump might not even run!

So - I can't conclude your method won't work or anything like that, but it would be a serious reservation on my part. Now - I would assume that the fancy-pants BMW bleed program would force the thermostat open. I wonder if your method would work better if you just connected a charger/power supply and used the bleed program to circulate instead of running the engine? Less risk of burns etc... too.

Related - for a couple of decades I've always tried to change fluids more often than manufacturer recommended. Often with fluids anywhere in the driveline (brakes, transmission, clutch, steering) I can observe improvements in the system after changing the fluid even when I do it "too often". One advantage of doing this is that one doesn't need to feel desperate to get ALL of the old fluid out. When I use a turkey baster to extract and replace all of the power steering fluid once per year or every other oil change or whatever, I don't need to get all stressed about removing every drop of it. What was left in the system is still "good enough" and will blend with the fresh fluid. Same for coolant, transmission, you name it. Taking this approach often means it's an easier job to do (e.g. turkey baster power steering reservoir and then refill instead of pulling banjo bolts at the rack to get every drop out)

Now - you found what appeared to be incorrect fluid so what I just said doesn't apply

Thank you for devising and posting and innovative way of performing this job, which BMW really made a PITA on the F10 by eliminating some drains and requiring a vacuum apparatus to refill.
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      03-20-2020, 09:27 AM   #7
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Quote:
Originally Posted by Surly73 View Post
I like that common sense is on the list of required items

A weakness that I see in this process is the fluid in the radiator loop. The coolant system isn't a single loop, there are branches all over the place and one of these is the entire radiator. The thermostat needs to be open to ensure you've got proper flow here.

With every inline 6 BMW I've worked on, (M52, M52TU, M54, N52, N55) I have found that even in the summer heat when it's just idling and I have the hood up it sheds enough heat to the environment that the thermostat doesn't even necessarily open. (stop and go traffic in the blazing sun with the AC on is a different environment than idling in the shade in my garage with everything off and the hood open). On the N series engines with electric water pump, if the weather is cool the pump might not even run!

So - I can't conclude your method won't work or anything like that, but it would be a serious reservation on my part. Now - I would assume that the fancy-pants BMW bleed program would force the thermostat open. I wonder if your method would work better if you just connected a charger/power supply and used the bleed program to circulate instead of running the engine? Less risk of burns etc... too.

Related - for a couple of decades I've always tried to change fluids more often than manufacturer recommended. Often with fluids anywhere in the driveline (brakes, transmission, clutch, steering) I can observe improvements in the system after changing the fluid even when I do it "too often". One advantage of doing this is that one doesn't need to feel desperate to get ALL of the old fluid out. When I use a turkey baster to extract and replace all of the power steering fluid once per year or every other oil change or whatever, I don't need to get all stressed about removing every drop of it. What was left in the system is still "good enough" and will blend with the fresh fluid. Same for coolant, transmission, you name it. Taking this approach often means it's an easier job to do (e.g. turkey baster power steering reservoir and then refill instead of pulling banjo bolts at the rack to get every drop out)

Now - you found what appeared to be incorrect fluid so what I just said doesn't apply

Thank you for devising and posting and innovative way of performing this job, which BMW really made a PITA on the F10 by eliminating some drains and requiring a vacuum apparatus to refill.
You make very good points regarding that there are multiples loops. I was under the assumption that the thermostat would open up once the car was getting up to temp or whatever. I drained out about 10 gallons of old coolant and antifreeze total so if what you say is true I'm sure I got multiple systems flushed. I also ran the bleed procedure to monitor the content of the fluids color and it all seemed to be blue. I will keep your advice in mind next time. The reason I have this fluid flush mentality is because I don't know what the previous owner put in the car. It bought it at 100k and when doing the valve cover gasket we found out he was using conventional oil. With this and the coolant being green I decided that this previous owner didn't know what he was doing and thus I needed to get as much old fluid out while I can.
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      03-20-2020, 09:51 AM   #8
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Quote:
Originally Posted by Surly73 View Post
I like that common sense is on the list of required items

A weakness that I see in this process is the fluid in the radiator loop. The coolant system isn't a single loop, there are branches all over the place and one of these is the entire radiator. The thermostat needs to be open to ensure you've got proper flow here.

With every inline 6 BMW I've worked on, (M52, M52TU, M54, N52, N55) I have found that even in the summer heat when it's just idling and I have the hood up it sheds enough heat to the environment that the thermostat doesn't even necessarily open. (stop and go traffic in the blazing sun with the AC on is a different environment than idling in the shade in my garage with everything off and the hood open). On the N series engines with electric water pump, if the weather is cool the pump might not even run!

So - I can't conclude your method won't work or anything like that, but it would be a serious reservation on my part. Now - I would assume that the fancy-pants BMW bleed program would force the thermostat open. I wonder if your method would work better if you just connected a charger/power supply and used the bleed program to circulate instead of running the engine? Less risk of burns etc... too.

Related - for a couple of decades I've always tried to change fluids more often than manufacturer recommended. Often with fluids anywhere in the driveline (brakes, transmission, clutch, steering) I can observe improvements in the system after changing the fluid even when I do it "too often". One advantage of doing this is that one doesn't need to feel desperate to get ALL of the old fluid out. When I use a turkey baster to extract and replace all of the power steering fluid once per year or every other oil change or whatever, I don't need to get all stressed about removing every drop of it. What was left in the system is still "good enough" and will blend with the fresh fluid. Same for coolant, transmission, you name it. Taking this approach often means it's an easier job to do (e.g. turkey baster power steering reservoir and then refill instead of pulling banjo bolts at the rack to get every drop out)

Now - you found what appeared to be incorrect fluid so what I just said doesn't apply

Thank you for devising and posting and innovative way of performing this job, which BMW really made a PITA on the F10 by eliminating some drains and requiring a vacuum apparatus to refill.
Good point about the thermostat. If you're adding in room temperature distilled and flushing it, it very likely won't get hot enough to trigger the thermostat. That said, it wouldn't make sense for the bleed procedure to NOT open the thermostat. After all, the radiator is probably the most important part of the cooling system, so to allow air to stay in there seems foolhardy.

Assuming the bleed procedure bleeds the entire system, it seems a better option to use the bleed procedure to flush the system, rather than run the car.
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      03-20-2020, 11:40 AM   #9
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If the highest part of the cooling system is lower than any of the passages in the engine you have a very strong probability of air bubbles and hot-spots. That's why bleeding procedures are developed. I don't know if the family of BMW engines are designed that way. I know it wasn't a BMW, but my last car would overheat just by looking at it if the bleeding procedure wasn't followed 100%.

Just be careful.
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      03-20-2020, 05:26 PM   #10
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This is very useful. I actually used the same coolant tube and an external hose. I kept bleeding it with engine off, and only about 2 gallons at a time came out. I do have the Schwaben fill tool, do you think I should use that in conjunction with the method you just used?
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      03-20-2020, 05:46 PM   #11
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Quote:
Originally Posted by Sylverlee View Post
This is very useful. I actually used the same coolant tube and an external hose. I kept bleeding it with engine off, and only about 2 gallons at a time came out. I do have the Schwaben fill tool, do you think I should use that in conjunction with the method you just used?
Many people are saying it might be better to have the car on accessory mode and to run the bleed procedure but in my opinion it's better to have the car running. My theory is that the car still circulates the coolant without draining the battery power. I did the bleed procedure at the end just to make sure air pockets didn't form. For me, I got about 10 gallons of fluid out while I was putting distilled water in the system. Roughly 5 gallons of old coolant and the rest was distilled water going into my return bucket. Do with this as you may but I found this to be the most efficient process
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      03-21-2020, 10:36 AM   #12
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Quote:
Originally Posted by David_Vasha View Post
Many people are saying it might be better to have the car on accessory mode and to run the bleed procedure but in my opinion it's better to have the car running. My theory is that the car still circulates the coolant without draining the battery power. I did the bleed procedure at the end just to make sure air pockets didn't form. For me, I got about 10 gallons of fluid out while I was putting distilled water in the system. Roughly 5 gallons of old coolant and the rest was distilled water going into my return bucket. Do with this as you may but I found this to be the most efficient process
Does the car circulate the entire system when you run the bleeding procedure? I wonder why mine only did 2gallons (didn't continue adding while running which I'm learning now is prob pretty bad).
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      03-21-2020, 11:16 AM   #13
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Quote:
Originally Posted by Sylverlee View Post
Quote:
Originally Posted by David_Vasha View Post
Many people are saying it might be better to have the car on accessory mode and to run the bleed procedure but in my opinion it's better to have the car running. My theory is that the car still circulates the coolant without draining the battery power. I did the bleed procedure at the end just to make sure air pockets didn't form. For me, I got about 10 gallons of fluid out while I was putting distilled water in the system. Roughly 5 gallons of old coolant and the rest was distilled water going into my return bucket. Do with this as you may but I found this to be the most efficient process
Does the car circulate the entire system when you run the bleeding procedure? I wonder why mine only did 2gallons (didn't continue adding while running which I'm learning now is prob pretty bad).
I assume that the car circulates the coolant given that it needs to be recooled once heated. You always want to add fluid to get the old fluid out. I kept adding distilled water until I saw clear distilled water coming out of the hose.
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      03-21-2020, 01:29 PM   #14
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Quote:
Originally Posted by Sylverlee View Post
Does the car circulate the entire system when you run the bleeding procedure? I wonder why mine only did 2gallons (didn't continue adding while running which I'm learning now is prob pretty bad).
Running a pump dry fucks the pump. A water pump replacement might be in your near future.
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      03-21-2020, 05:21 PM   #15
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Running a pump dry fucks the pump. A water pump replacement might be in your near future.
damn it haha.. Was following someone else's directions. This is even if the car was only on accessory and engine not running?
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      03-21-2020, 06:38 PM   #16
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Quote:
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damn it haha.. Was following someone else's directions. This is even if the car was only on accessory and engine not running?
Yea, any kind of liquid pump does NOT like being run dry. It depends on the liquid for lubrication, so once it's dry it starts damaging itself. The bleed process runs the pump to cycle the coolant. Come to think of it, the reason you only got 2 gallons out is probably because the pump just ran out of stuff to pump. There's definitely coolant passages/tubing that are lower than the pump, so once it runs out of stuff to pump, the fluid just collects in the lower areas.
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      03-21-2020, 09:10 PM   #17
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Quote:
Originally Posted by Unspec View Post
Yea, any kind of liquid pump does NOT like being run dry. It depends on the liquid for lubrication, so once it's dry it starts damaging itself. The bleed process runs the pump to cycle the coolant. Come to think of it, the reason you only got 2 gallons out is probably because the pump just ran out of stuff to pump. There's definitely coolant passages/tubing that are lower than the pump, so once it runs out of stuff to pump, the fluid just collects in the lower areas.
Yah that's what I figured. Ok but if I keep adding coolant, after 2 gallons wouldn't it just started pushing out the coolant I put in? When does the coolant passages/tubing begin to get pumped out?
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      03-21-2020, 11:10 PM   #18
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Question, for the bleeding process, people usually say it lasts for 12 minutes, but when I engage it it can last for 20 minutes plus until I stop the process manually. Do y'all know the reason behind this?
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      03-22-2020, 04:00 PM   #19
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Quote:
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Yah that's what I figured. Ok but if I keep adding coolant, after 2 gallons wouldn't it just started pushing out the coolant I put in? When does the coolant passages/tubing begin to get pumped out?
Sorry, not getting what you're asking. The process in theory should be:

Run bleeding procedure with vent tube draining into a bucket. Run bleed procedure and continuously add distilled water into the expansion tank, essentially flushing the system and replacing all coolant with distilled.

After your drain starts running clear, add into the expansion tank 5 liters of BMW antifreeze. In theory drain hose should still be only outputting distilled, since coolant hasn't reached the vent hose yet. Once added, turn off car to stop the venting procedure, and reattach the vent hose. You'll probably lose some distilled in the reattachment process, nothing to sweat about. Run the bleed process again and top off with distilled water to manufacturer recommended levels. Let the bleed process run for a while to properly mix the antifreeze and water.
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      05-11-2020, 11:22 PM   #20
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So, I tried the bleeding method today. I'm not sure how well it flushes out the system, but god damn that pump can MOVE. At the peak of the bleeding process, it can pump almost as fast as I can pour. 100% a two man job if you're trying to be neat and not spill coolant all over your garage floor. Also, you better have a lot of distilled water and a place to drain all that coolant (please don't just drain it into the street). As in, 10-15 gallons. Why? I'm pretty sure the bleed process bleeds the system out in parts. Not sure about the order, but for example it might do radiator, then heater core, then engine, then aux rad, etc. I really don't think it's cycling the entire coolant system at once, I'll explain why I think this in a second. So to flush the entire system, you need to stand there and pour in distilled water for the entire 10 or so minutes the bleeding cycle takes.

After the bleeding cycle stopped for the distilled water flush, I then just dumped a straight 5L of coolant into the system. But what is this? The water that was coming out at the end of the bleed cycle before was almost clear, but now it's a deep dark blue! This is what makes me think that the system doesn't just cycle the entire coolant system at once, and instead does parts. So it very quickly starts spitting out your coolant mixed with some water after a bit. It still got enough of the coolant into the entire system to read a -30ish*C freeze protection on my coolant tester, but I'm not really happy with how this coolant flush works. I think the best bet is still the BMW recommended method of radiator hose pull, followed by using the vacuum tool air purge and refill. You also don't risk starving the pump and having it die prematurely because it's gulping air.

Interestingly enough, the tubes from those harbor freight hand transfer pumps are the perfect size for this. You can just jam it into the bleeder hose and it won't leak at all.
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      05-12-2020, 12:41 PM   #21
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Quote:
Originally Posted by Unspec View Post
So, I tried the bleeding method today. I'm not sure how well it flushes out the system, but god damn that pump can MOVE. At the peak of the bleeding process, it can pump almost as fast as I can pour. 100% a two man job if you're trying to be neat and not spill coolant all over your garage floor. Also, you better have a lot of distilled water and a place to drain all that coolant (please don't just drain it into the street). As in, 10-15 gallons. Why? I'm pretty sure the bleed process bleeds the system out in parts. Not sure about the order, but for example it might do radiator, then heater core, then engine, then aux rad, etc. I really don't think it's cycling the entire coolant system at once, I'll explain why I think this in a second. So to flush the entire system, you need to stand there and pour in distilled water for the entire 10 or so minutes the bleeding cycle takes.

After the bleeding cycle stopped for the distilled water flush, I then just dumped a straight 5L of coolant into the system. But what is this? The water that was coming out at the end of the bleed cycle before was almost clear, but now it's a deep dark blue! This is what makes me think that the system doesn't just cycle the entire coolant system at once, and instead does parts. So it very quickly starts spitting out your coolant mixed with some water after a bit. It still got enough of the coolant into the entire system to read a -30ish*C freeze protection on my coolant tester, but I'm not really happy with how this coolant flush works. I think the best bet is still the BMW recommended method of radiator hose pull, followed by using the vacuum tool air purge and refill. You also don't risk starving the pump and having it die prematurely because it's gulping air.

Interestingly enough, the tubes from those harbor freight hand transfer pumps are the perfect size for this. You can just jam it into the bleeder hose and it won't leak at all.
So in this method you're just attaching a hose to the coolant tank hose and then running the bleeding method? I tried this and only got like 3 gallons, but wasn't pouring in distilled water at the same time (now realizing that was prob a bad move for the water pump). You got 10 gallons out? Was that all water half way through, or was it still some coolant? If you're feeding it water the entire time, is the water pump actually still being starved?
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      05-12-2020, 09:46 PM   #22
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Quote:
Originally Posted by Sylverlee View Post
So in this method you're just attaching a hose to the coolant tank hose and then running the bleeding method? I tried this and only got like 3 gallons, but wasn't pouring in distilled water at the same time (now realizing that was prob a bad move for the water pump). You got 10 gallons out? Was that all water half way through, or was it still some coolant? If you're feeding it water the entire time, is the water pump actually still being starved?
I remember talking about this with you in the other thread

Yep, you pull the return/overflow line and use whatever method to extend it. I got probably close to 8 gallons before it started to run clearish. Water all the way through, you want to replace the entire system with distilled water. Once you've done that, you know there's 10 liters of water, so you need to drain 5 liters of that out and replace with 5 liters of coolant. I did that by running the bleed cycle a second time (turn car off and wait for 3 minutes before running it again). Once you've added all the antifreeze you need, quickly jam the return hose back onto the nipple. Adjust the coolant level as needed.

I'd suggest people to drive around a few times, and check with a coolant tester. Proper 50/50 mix will protect down to -37*C. Add coolant or water as needed to the expansion tank to adjust the mix.
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