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-   -   Trapped air in the cooling system woo woo !!! (http://www.bimmerfest.com/forums/showthread.php?t=658325)

robertobaggio20 11-15-2012 08:18 AM

Trapped air in the cooling system woo woo !!!
 
Hi Everyone,

Recently, I had to change my radiator as my bleed screw socket's thread got screwed and it was too tempting not to try to change the rad as my fan clutch was not in the way.

So I changed the rad. Needed to fill up 10 quarts of water and coolant concentrate or nearly that, including bleeding.

Watched for a few days and noticed that the water level was dropping fast. Topped up to full again 3 days later and did bleeding for the heck of it. Not much bubbles showed up.

Water levels kept dropping, much faster than my old radiator. I feared the worse...i do have a leaky HG for nearly a year, and there is some coolant and oil loss but its tolerable so I've left it. Suddenly it seemed to be worse, and this is a new radiator !

I feared the worse, particularly because a discussion on steel seal, blown HGs etc was going on over here at the same time. My teeth started a-chattering.

Now, when you have a blown HG or a cracked head and you're losing coolant, combustion gases will get into the cooling system, and coolant would go out the tailpipe. Open your rad cap and you'll see tiny bubbles showing up. I topped up water for the 3rd time, and decided to man up and check for bubbles. I also shot a video. The Padre has kindly uploaded it for me :

http://youtu.be/a-lO-f1zJ34

Its a 90 second video. The engine is pretty loud so please turn down the volume a bit.


Scary right ? I braced myself to do a compression test etc etc. Not happy at all.

So I decided to poll my team. Spoke to my regular mechanic. Finally, a sigh of relief. Here's why.

When you change your radiator, alot of air gets into the system. This makes its way into the expansion tank and looks like falling coolant levels. You may require between 2-3 topups in short order for the coolant levels to stabilise and fall at normal rates (M50 engines, the coolant level drops from max to under 1/2 over 6-8 weeks, and you'll need to top up.) This is normal. This is not dangerous to the engine in any way.

After I shot that video, I monitored the situation twice a day. Water dropped again to the 3/4 mark fairly quickly, and then dropped more slowly..about a mark a day. Yesterday, 20 days after the rad was changed and after 3 prior full topups and bleeds, it was at the cold mark (1/2) when cold, and after a long drive, it was 1 mark higher. While the engine was still very hot, I opened the rad cap. The water level immediately rose up to slightly above the full mark. There was no shooting out. This is a normal response to depressurisation on a normal radiator that is initially pressurised.

Here's the thing :

There was NO HINT of overheating through this entire saga, and I drive my car every day.

My MkII eyeballs were practically glued to the temp gauge throughout this whole period. The car's performance was perfectly normal under all kinds of driving conditions. Each time I topped up water, I bled the car, and apart from the first time when I did this after changing the radiator, there were hardly any bubbles seen during the other bleedings. Yet, the fast drop in coolant levels indicated (in this case) the presence of air pocket accumulating itself out at the expansion tank.

So these are my real world observations. From this, I make the following conclusions.

1. Bleeding is easy.
2. There will always be air in the cooling system.
3. The car is PERFECTLY FINE with LOTS of air in the cooling system. It is very very unlikely for these to accumulate into a sufficiently large air pocket to actually cause problems, if you bled the car according to the Bentley manual's instructions correctly. The cooling system is designed to evacuate all this air out to the expansion tank during driving. I'm assuming that nothing is wrong with your cooling system, particularly the radiator, water pump and thermostat.
4. If you have trouble bleeding, you are not doing it right.
5. If you have bled correctly, and your car is running hot or overheating, you have a different problem in either your cooling system or the engine.

I hope this post and that video in particular helps us put to bed the overwhelming fear that some of us feel about air in the cooling system. Even I freaked out when I saw that stuff. Writing this post, I recall the emotions of that period, and now genuinely feel the sense of relief that all is well, all over again.

How to bleed your radiator (m20/m50)

1. Start when the car is cold.
2. Open the rad cap and bleed screw (m20 engines have an extra one on the thermostat housing).
3. Fill up water into the expansion tank at an even pace until it runs out of both bleed holes. At that point fill up slowly (just to save water) until all the bubbles seem to have run out from both holes, then stop pouring.
4. Start the engine and set cabin heat to high. Blower does not need to be activated.
5. Let the car reach operating temperature ...might take you up to 10 minutes.
6. Pour water into the expansion tank and watch it run out of the bleed hole. There should be a few more bubbles (but its ok if there are none).
7. At some point, only coolant will run out. While pouring water into the expansion tank with one hand, quickly tighten the bleed screw down over the water pouring out of the bleed hole.
8. When the water flow has stopped, stop pouring water and tighten the bleed screw with a screwdriver or a coin. Do not overtighten, you will strip the threads. As long as it feels kinda tight, its fine. Once again, if you keep tightening, it will keep turning....do not do this. I must have done this somewhere along the line which was how I screwed my old radiator.
9. M20 engines will have to repeat step #8 with both bleed screws alternately.
10. After this, fill up water in the expansion tank right to the brim, then fix the rad cap back and tighten it good. Don't worry about jamming the water down, compressing the water, etc. It does not happen.
11. Don't rush through this. That being said, its not a delicate task either. Each bleeding either side of a cold/hot engine would only take about 3 minutes. Add 10 minutes to heat up your engine and you've got a total of 16 minutes for bleeding.

12. If you like, and if you feel you have not reached the Tibetan E34 owner's league's state of nirvanic Utmost Peace of Mind, then drive the car for a day or a couple of days, then repeat the bleeding process once again from scratch. And, even if you notice alot of bubbles this time, do not bleed a third time. NO NEED. There will always be air bubbles. It is designed into the system.

13. Please note that the Bently manual suggests a slightly different method, that involves buttoning up the system after the cold bleed, then starting the engine and only opening the bleed screw after it heats up, then closing it after all the bubbles have left, then shutting down the car and topping up coolant if needed. I am sure this works fine, but I believe the process I use above is faster overall as the E34 can take up to 4 hours to cool all the way down.

Enhanced bleeding methods used successfully by festers but entirely unnecessary in my opinion:

1. Pouring hot water into the top radiator hose.
2. Blowing into the expansion tank during cold bleeding (although this is a good method to flush out more dirt during a rad flush than merely by running water, I've been told on good authority).
3. Attaching an air compressor to the expansion tank's mouth to pressurise the system during a cold bleed.
4. Creating a long tubelike funnel afixed to the expansion tank, standing on a chair and pouring water into it.
5. Parking the car on an incline or elevating the front of the car with a jack and jack stands, before bleeding.

I invite comment to this thread, but especially anyone who chooses to criticise, please, view that video first. It is the pivot for this post, essentially.



rgds,
Roberto

Monsignor 11-15-2012 09:07 AM

Quote:

Originally Posted by robertobaggio20 (Post 7196477)
Enhanced bleeding methods used successfully by festers but entirely unnecessary in my opinion:

1. Drilling holes into the thermostat's flange.
4. Attaching an air compressor to the expansion tank's mouth to pressurise the system during a cold bleed.

Roberto, in exchange for uploading the video, I respectfully ask that you remove these two from your list. In no routine maintenance of any car ever in any system of said car at any point in time in the history of the automobile was drilling ever necessary. I would be disheartened if a fellow 'fester f*cked up their car with a power tool over something as silly as this.

An aircompressor also is not something needed in any car for this particular task. Routine maintenance requires a running motor to pressurize the system naturally, not with over pressuring it with your artificial pressure.

dc_wright 11-15-2012 01:57 PM

Unfortunately steps 4 and 5 of your bleeding process are incorrect. You do not run the engine and bring it up to temperature. If you re-read your Bentley manual where it directs to start the engine is AFTER you have run sufficient coolant to complete the bleeding process (no air bubbles coming out), replaced the bleed screw, and replaced the reservoir cap.
When you are adding coolant to do the bleeding process you do not "fill the reservoir up quickly", it must be done deliberately and very slowly otherwise you get more air entrapment.

How to bleed your radiator (m20/m50)

1. Start when the car is cold.
2. Open the rad cap and bleed screw (m20 engines have an extra one on the thermostat housing).
3. Fill up water into the expansion tank quickly until it runs out of both bleed holes. At that point fill up slowly (just to save water) until all the bubbles seem to have run out from both holes, then stop pouring.
4. Start the engine and set cabin heat to high. Blower does not need to be activated.
5. Let the car reach operating temperature ...might take you up to 10 minutes.

robertobaggio20 11-15-2012 04:08 PM

Quote:

Originally Posted by dc_wright (Post 7197147)
Unfortunately steps 4 and 5 of your bleeding process are incorrect. You do not run the engine and bring it up to temperature. If you re-read your Bentley manual where it directs to start the engine is AFTER you have run sufficient coolant to complete the bleeding process (no air bubbles coming out), replaced the bleed screw, and replaced the reservoir cap.
When you are adding coolant to do the bleeding process you do not "fill the reservoir up quickly", it must be done deliberately and very slowly otherwise you get more air entrapment.

How to bleed your radiator (m20/m50)

1. Start when the car is cold.
2. Open the rad cap and bleed screw (m20 engines have an extra one on the thermostat housing).
3. Fill up water into the expansion tank quickly until it runs out of both bleed holes. At that point fill up slowly (just to save water) until all the bubbles seem to have run out from both holes, then stop pouring.
4. Start the engine and set cabin heat to high. Blower does not need to be activated.
5. Let the car reach operating temperature ...might take you up to 10 minutes.


Hi DC,

I took another look at the Bentley manual. You are correct, it says differently. You're supposed to bleed it once with the engine cold, then fix the bleed screw and rad cap, then start the engine with cabin heat onto high, wait till the car reaches optemp, then merely loosen the bleed screw, more coolant and bubbles will run out, then replace the bleed screw when only coolant runs out, then shut the engine down, and top up the radiator if the water level has fallen.

Well, I'm sure this method works fine if its in the manual, but the method I use eliminates the need and the time taken to stop the engine, let it cool down (which can take up to 4 hours), and then top up coolant. That would essentially be the same as doing 2 bleed cycles on 2 separate days (for practicality), which I've found to be unnecessary, but I still sometimes do so for the fun of it.

That being said, I'm going to do what the manual suggests on my next flush to see if there's any significant difference.

Secondly, while you are correct that pouring in water quickly may introduce air into the system in theory, in practice I do not believe it happens :

1. Expansion tanks always have some water in them usually, even if they are quite low in terms of the volume mark. When you pour water, air is not pushed in through the system, as the connection between the expansion tank and the radiator is at the bottom and the pre-existing coolant serves as a blockage to that opening.

2. Even if air goes in, it gets trapped in the vertical space right under the bleed screw and does not circulate around as the engine is still off and the wp is not functioning. So when you do the cold bleed, this air gets evacuated.

3. When the engine is started and 10 minutes is allowed to pass, any additional air that you somehow introduced into the system will circulate and accumulate under the bleed screw without entering the engine as the thermostat would have been closed for the first 3-5 minutes of the engine's operations and the coolant coming from the radiator circulates past the thermostat and returns to the radiator without entering the block. And of course, it can be easily bleeded out when you do the hot bleed.

4. When you do major cooling system stuff like replacing engines, or radiators, no matter how carefully you pour coolant in, air will remain trapped in the system. This is not dangerous to the engine. All you'll have to do is to top up coolant more than once if the water levels appear to fall quickly over the subsequent days. Remember, the dropping coolant level is actually air in the system accumulating itself out into the expansion tank (when there is alot of air still left). So in such situations especially it would be nice to do a second bleed cycle a few days later. Under normal situations such as radiator flushes, only one bleed cycle is needed.

Regardless, your points are well taken and I will ammend my OP accordingly. Thank you.



rgds,
Roberto

p.s. Padre, my op has been ammended.

Monsignor 11-15-2012 04:16 PM

Jesus.

http://lmgtfy.com/?q=Terse+definition

robertobaggio20 11-15-2012 09:38 PM

Quote:

Originally Posted by 95 E34 (Post 7197345)


"Jesus" is terse indeed, and relevantly so. Will work on being cogent sir. Apologies.


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