Different people have used different methods, so yeah there are some conflicting stories on this.

The most common way is to very slowly fill the coolant in the ET with the bleeder screw out and engine off until no bubbles come out and the ET is full. The heater valve is open with key out, so I don't bother turning the heater on at all. Take it for a nice long drive, let it cool down for several hours, then top up. Check the level again a couple more times in the days to follow.

Hopefully others will post their own methods and explain the reasoning and maybe we'll have a consensus?

 

poke a hole in the upper hose and start the engine. you will get nos spray with this mod after engine warms up.

 

I pretty much do it the standard way everyone does it here with a few extras I found that helped me out. Heat on high engine off, fill until it comes out of bleed screw without any bubbles. I also like to give the hoses a few good squeezes to make sure they are filled with water and not air. After I do that, I let it run to operating temp. I also like to give the engine some decent revs to get the coolant flowing while warming up. Sometimes that will knock a stubborn air bubble loose if your having trouble bleeding. If everything goes well, I check the coolant the next day to top off or add any as needed.

 

Did my cooling system saturday. Flushed the system out with the drain plug opened with 3 gallons of distilled water.

With the front end jacked up a bit, I filled the car cold with about a gallon and a half of 50/50 BMW coolant. Let the car run with the heater on for maybe 20 minutes or so, opening the bleeder screw here and there. After adding about the last half gallon or so, I took it for a short drive to circulate the coolant. Let it cool for a bit, opened the cap and added some more water. We went out to run some errands after that.

Checked it the next day when cold and added a bit more so the float would start to well, float.

That's it.

 

Park in nose-high position.
Remove ET cap and bleed screw.
Engine off.
Turn key to ON.
Set heat to max and turn on blower (halfway or so).
Pour coolant in until it overflows.
Keep pouring until it comes out the bleeder opening
Keep pouring until the coolant is bubble-free (this may take a minute or two).
You will spill a lot of coolant.
Top up ET.
Use turkey baster to remove excess coolant in the ET.
Reinstall bleeder screw and ET cap.

Check frequently over the next few days and top off as necessary.

^That's my technique and it's worked flawlessly multiple times for me.

 

^^^This method, especially the lifted front end part.^^^

 

Borrow/pay to use a vacuum coolant refill kit. 99% guaranteed no air trapped.
When my buddy isn't around, I jack up the front end, heater on max with engine off, bleeder screw open. Sometimes you need to run the engine for a few minutes to push the air to the bleeder area, then rebleed.

 

The real key is to pour in the coolant slowly. Too fast and you'll trap bubbles that will be hard to get out.
Lifting the front isn't necessary, but if it's already jacked up I'd leave it that way while bleeding.

 

There's no "different method." There's only the correct method. Which is on my cooling site/blog/page/post etc.

 

Do what Mango says!!!

 

I picked up a right angle drill a while ago, and got into the habit of running the WP with it to flow the coolant, this is probably the most over the top method though.

I usually also put a bit of clear tubing in the bleed hole leading to a jug so I don't spill. It takes a while to bleed these cars and you should keep an eye on the coolant level for the next couple weeks.

 

When I first bled the e46, it took me 3 pages of posts to figure out the ENGINE IS OFF THE ENTIRE TIME.

No one EVER explains this right, so I will say it again.
ENGINE IS OFF THE ENTIRE TIME.
ENGINE IS OFF THE ENTIRE TIME.
ENGINE IS OFF THE ENTIRE TIME.

1. Did the cold bleed (Key ON, ENGINE OFF, heater 91, fill tank until bleed overflows, blew into tank neck for good measure, no air bubbles, close bleed, siphon excess, dipstick still bobbing)
2. Started the car.
3. Turned on 19/7 OBD temp monitor
4. Drove around until full operating temp, and temp. started cycling between 96-100C. (This was way after temp needle was at noon)
5. Heater: I got hot air from the windshield/dash vent, and the legs vent, but not the front facing clock/radio vent. I was switching b/w "Auto" and selecting the 3 arrow buttons. Bottom line, I got heat.
6. No exhaust smoke at startup. Saw exhaust smoke at a traffic light, but then it mostly went away. Sounds like condensation? I see moisture in tailpipe opening.
7. Drove home and parked car.
8. Jacked front and inspected for leaks. No leak on ground. No obvious leak at lower hose or base of tank coupling. Dry as a bone. Will verify tomorrow.

 

Thanks for all the replies guys!

 

This thread turned out a lot more civil than some past ones, thank goodness. Hot tempers and coolant theads don’t mix. :clap:

 

***What's the 100% correct way to bleed the cooling system after repair?***

The correct answer is "Till there is no air in the coolant system"

If any of you have ever taken your car to a professional shop for cooling system maintenance does the mechanic tell you to come back the next day so he can top off your coolant? Think about it.

I was reading this thread for fun and I have to laugh at some of the responses above - and since it is like an oil thread I was gonna just avoid posting till I read OnTheFence response above - especially when he says 3 times not to start the car. You got this from where - the BMW manual - a forum - certainly not from decades of bleeding various cooling systems on a wide variety of engines.

You posted a set of instructions here a year ago where you asked if an e46 should be bled like an e36. The ones you posted above are similar and I didn't say anything then. I will remark on two of them now though:

Keep pouring until the coolant is bubble-free (this may take a minute or two).
You will spill a lot of coolant.

You will spill coolant with the engine off as there is nothing (waterpump) pulling in the coolant and the bleed hole in the t-stat is only a pin hole - so the front end of the cooling system is full but you're trying to pour more in and only a minute amount can trickle through the t-stat bleed hole. Amateurs try to pour the coolant in quickly on a closed coolant system and it spills or overflows like a frothy beer in a mug. Professionals don't spill coolant on the floor since the engine is running the ET will be empty if the system is low and as you pour the coolant in the waterpump pulls it in, pushes it into the coolant channels and displaces trapped air which cycles around the system and purges out the ET. The other worrying thing is the air bubbles you are seeing are only at the ET - all the coolant that just went in carried air bubbles you are not seeing to the entire cooling system and that still needs purged and burped and that can't happen till it's circulating.


The other instruction I think is ridiculous is this one:

Check frequently over the next few days and top off as necessary.


If you'd bled with the engine running t-stat open, waterpump running - you wouldn't have to check several times over the next few days as you've removed the air via purging and burping the first time - in the professional world who has time for checking several times over a period of days? - is the customer going to bring their car back 4 days straight - you gotta be kidding - do it once - do it right - here's your bill - goodbye.


Your task 2 above in this thread says "start car" OK so the OP drives around and guess what - if there was an air pocket he'll be topping it off tomorrow (hopefully) when the engine is cold - maybe a third day as difficult trapped air in the spiral heater core get purged out now the waterpump is pushing coolant instead of air bubbles - I'm not attacking you individually and I realise that's how BMW basically phrased their instructions for the amateur home mechanic - but that was to make it safer - for them - from lawsuits. The BMW instructions are about liability mitigation. Not sure why everyone on here pays attention to them for bleeding - probably one of the reasons this forum has likely more threads about poor bleeding & issues than every other auto forum in the world combined.

This engine is not any different than any other pressurised cooling system in any other car. It has nooks and crannies and spots that will trap air. If you've lost or drained coolant it has been replaced by air. The coolant you pour in will contain air bubbles - these need purged and burped. Purging only occurs when the coolant is circulating - burping occurs when the trapped air behind the t-stat is allowed to escape through the bleed screw or ET cap.

Not gonna write a how to on bleeding a bloody engine - but if you have questions - do a Google Search and read how an engine is bled with it running - don't pay attention on this forum for this aspect of e46 maintenance. - pros do it with the engine running Doing it cold with nothing running to purge the air just means you hope that after your next drive the air has been moved to the ET where you can just top it off per the safe amateur instructions - well you're really doing the same thing - just in two different stages and possibly without the same results in addition to possibly driving the car low on coolant before top off. Often the trapped air doesn***8217;t get moved even after driving since you***8217;ve now closed the system and air compresses much easier than coolant with pressure and the result is 40,000 threads about e46 bleeding issues.

Edit: and ..... the reason many raise the front end when bleeding/topping off is so the escape route for air (ET hole or bleed screw) is higher than any other coolant component - meaning the air can be pushed through and as we all know air rises in liquid - can escape.

 

***What's the 100% correct way to bleed the cooling system after repair?***

The correct answer is "Till there is no air in the coolant system"

If any of you have ever taken your car to a professional shop for cooling system maintenance does the mechanic tell you to come back the next day so he can top off your coolant? Think about it.

I was reading this thread for fun and I have to laugh at some of the responses above - and since it is like an oil thread I was gonna just avoid posting till I read OnTheFence response above - especially when he says 3 times not to start the car. You got this from where - the BMW manual - a forum - certainly not from decades of bleeding various cooling systems on a wide variety of engines.

You posted a set of instructions here a year ago where you asked if an e46 should be bled like an e36. The ones you posted above are similar and I didn't say anything then. I will remark on two of them now though:

Keep pouring until the coolant is bubble-free (this may take a minute or two).
You will spill a lot of coolant.

You will spill coolant with the engine off as there is nothing (waterpump) pulling in the coolant and the bleed hole in the t-stat is only a pin hole - so the front end of the cooling system is full but you're trying to pour more in and only a minute amount can trickle through the t-stat bleed hole. Amateurs try to pour the coolant in quickly on a closed coolant system and it spills or overflows like a frothy beer in a mug. Professionals don't spill coolant on the floor since the engine is running the ET will be empty if the system is low and as you pour the coolant in the waterpump pulls it in, pushes it into the coolant channels and displaces trapped air which cycles around the system and purges out the ET. The other worrying thing is the air bubbles you are seeing are only at the ET - all the coolant that just went in carried air bubbles you are not seeing to the entire cooling system and that still needs purged and burped and that can't happen till it's circulating.


The other instruction I think is ridiculous is this one:

Check frequently over the next few days and top off as necessary.


If you'd bled with the engine running t-stat open, waterpump running - you wouldn't have to check several times over the next few days as you've removed the air via purging and burping the first time - in the professional world who has time for checking several times over a period of days? - is the customer going to bring their car back 4 days straight - you gotta be kidding - do it once - do it right - here's your bill - goodbye.


Your task 2 above in this thread says "start car" OK so the OP drives around and guess what - if there was an air pocket he'll be topping it off tomorrow (hopefully) when the engine is cold - maybe a third day as difficult trapped air in the spiral heater core get purged out now the waterpump is pushing coolant instead of air bubbles - I'm not attacking you individually and I realise that's how BMW basically phrased their instructions for the amateur home mechanic - but that was to make it safer - for them - from lawsuits. The BMW instructions are about liability mitigation. Not sure why everyone on here pays attention to them for bleeding - probably one of the reasons this forum has likely more threads about poor bleeding & issues than every other auto forum in the world combined.

This engine is not any different than any other pressurised cooling system in any other car. It has nooks and crannies and spots that will trap air. If you've lost or drained coolant it has been replaced by air. The coolant you pour in will contain air bubbles - these need purged and burped. Purging only occurs when the coolant is circulating - burping occurs when the trapped air behind the t-stat is allowed to escape through the bleed screw or ET cap.

Not gonna write a how to on bleeding a bloody engine - but if you have questions - do a Google Search and read how an engine is bled with it running - don't pay attention on this forum for this aspect of e46 maintenance. - pros do it with the engine running Doing it cold with nothing running to purge the air just means you hope that after your next drive the air has been moved to the ET where you can just top it off per the safe amateur instructions - well you're really doing the same thing - just in two different stages and possibly without the same results in addition to possibly driving the car low on coolant before top off. Often the trapped air doesn't get moved even after driving since you've now closed the system and air compresses much easier than coolant with pressure and the result is 40,000 threads about e46 bleeding issues.

Edit: and ..... the reason many raise the front end when bleeding/topping off is so the escape route for air (ET hole or bleed screw) is higher than any other coolant component - meaning the air can be pushed through and as we all know air rises in liquid - can escape.

My thought on why BMW recommends filling the cooling system while the engine is not running is because this procedure both eliminates the air and saves time:

When the system is filled with coolant some air will be trapped inevitably. Obviously, this trapped air is nog going to be removed if the engine isn't running - you need the coolant to start circulating to get the bubbles out.
However, the design of the upper radiator hose doesn't seem to allow efficient removal of the circulating bubbles through the open bleeder screw - the hose is just too wide and a lot of the air will just pass by the screw hole. It doesn't matter, because ultimately the circulating air will end up in the expansion tank, where most of the actual "bleeding" occurs.

So, why wasting time staring at the screw hole with the engine idling? It is better to close the system and take the car for a test drive, keeping an eye on the engine temp rather than the bleeder.
There is also a better chance to get the pockets of trapped air to circulate while the car is moving and the engine runs at higher RPMs.

After cooling system work, I just drive around the block until I am confident the engine gets to proper operating themp and stays there, then check visually for leaks.
Then I just park the car. I know that when I check the coolant level on the next day, it will be 2-3 oz low, butif everything is done right, I don't need to top it off multiple times.

 

I'll just say that the comment above "until there's no air in the system" is pretty good...but...not knowing all the readers, I'll just say "except for the air in the top of the ET." Very important 'buffer' against your system blowing up.

I use this method after filling it up and then I'll drive it around the block a few times...and will also make sure I check the level every few days for a week at least...and only fill to between min and max so I do not overfill it.

With car cold and ET just filled to the top after complete system draining...

Close bleeder and ET cap. Heater on highest temp...fan on low.

Start car, rev to 4,000 rpms for 20 secs.

Turn car off.

Inspect/adjust level of coolant.

Repeat as necessary.

 

Heater on highest temp...fan on low.

A question for the masses: why do we turn on the heater at all when the heater valve is already open with key off?

This bit me once (back in my early E46 naive days) when I was trying to bleed coolant on a very hot SoCal afternoon, near 100F ambient temp. The heater valve didn’t open because it was above 91F, the maximum heater setting!

 

I think no matter what, we're all going to have our own ways of bleeding the system, like mentioned.
A shop won't tell you to come back. Why do you think?

My guess is they have something similar to this air purge tool.

https://www.ecstuning.com/b-schwaben-parts/coolant-refill-air-purge-tool/003466sch01/

 

Man, I'd love to pick one of those up. but I like my spinning the WP pump method too.

Friend bought a 325i on my recommendation. We were doing the cooling system as you do on a newly purchased E46 and he was very confused as to why I had brought out the drill.

 

Just a heads up, this happened to me twice now. A brand new upper coolant hose (hose to expansion tank) comes with a brand new bleeder screw installed already inside the hose. If you remove that bleeder, put another brand new one in its place don't re use that bleeder that came with the hose. The o ring has already been crushed and may not seal properly. Again, it's happened to me twice now on two separate cars. Double check afterwords you have no coolant leaks!


Sent from my iPhone using Tapatalk

 

I read one post about the spinning water pump using a drill attachment - neat concept but how do you get the t-stat open doing that so the coolant can circulate?

 

Car is on, and heater is set. Basically the spinning is just to speed up the process.

 

My Cooling System Filling Method -- assuming fill after repairs/service

The cooling system capacity is roughly 10 quarts. The goal is to fill the system with a mix of 50/50 water and anti-freeze. There is ample debate on the viability of using water from your hose or distilled water, I will not weigh in on that debate. I will, however say that you should flush the engine block and heater when the cooling system is open, and I use my garden hose for this task. You can find the block drain and empty the block if you want, I do not bother.

Back to filling the system.

When you mount the new radiator and make all connections, leave the connection of the Top Hose and the Radiator open. Pour your coolant mixture into the top hose until it comes out of the inlet on the radiator. Since I have just finished flushing the block with my garden hose, and the system holds 10 quarts, then if I pour in a gallon of pure anti-freeze, then I will have a near 50/50 mix at this point if I have not drained the block after flushing it. If the block and radiator are empty, then I pour in a full gallon of pure anti-freeze, then a gallon of water, this gives me 50/50 mix. Then I take a second gallon of pure anti-freeze and divide it among the empty gallon jug and the jug that the anti-freeze comes in, and fill both jugs with water until full. This gives me two more gallons of 50/50 mix. I continue to fill the block through the top hose (key to Position II (RUN) before Engine Start, heater controls set to high so the heater valve is open) until coolant comes out of the inlet where the top hose should be connected. This fills the block and heater, and then fills the radiator and expansion tank.

Connect the top hose to the radiator and check for leaks, bleed as necessary.

My experience is that if you have an empty radiator, and fill the expansion tank, the cooling system is well below capacity and the engine will over heat. If you fill the system through the top hose, then it will be filled to capacity will not overheat while trying to bleed it. The transfer tube that moves coolant from the expansion tank to the radiator is not very large, and you get a full tank and empty radiator, which makes bleeding very difficult. You can get around this by filling the entire system via the top hose where the fluid flows into the block, into the radiator via the bottom hose, and into the expansion tank via the heater hoses. When the entire system is filled, coolant will come out of the radiator where the top hose is supposed to be connected. Bleeding is quick and easy after that.

 

I'm not trying to force anyone to bleed the same way I do. There is no right or wrong way as long as you get the air out - just ways that take longer, have a higher risk of poor results and put your engine at temporary risk.

I thought I'd add a little more info to let folks fully appreciate why I bleed with the engine running and hardly ever use the bleed screw.

Here's what you're up against - you've done system work which removed coolant. - You now have air where that coolant was. The two highest areas of this coolant system (remember air rises in liquids) are the heater core and the expansion tank. Air that is inside the engine block now or worked it's way into the hoses and heater core needs to be removed. New coolant just poured in is much more oxygenated (meaning it has air bubbles) and these air bubbles will join to form small air pockets - these also need to be removed. Much of this air is now behind your thermostat and inside the engine block and heater core

You want an unobstructed circulation system so that any liquid you pour in can easily displace the air. To best accomplish that the heater valve should be open and the thermostat should be open. Both act like small dams - controlling the flow of coolant at times to maintain certain conditions. Depending on the status of the engine - one or both may be closed while you are attempting to fill with coolant. This is not optimal.

The thermostat on the e46 unlike many common auto t-stats does not have a bleed hole directly on the face of the dam (see image #2) - it has a pin hole in the plastic t-stat housing (image #3). If you are bleeding with the engine cold and t-stat closed ALL of the coolant that goes toward the t-stat housing must flow through this pin hole to reach the engine block and coolant channels. Alternately coolant can come from the other direction of the circulation but that direction includes the heater valve and a considerable uphill routing of hoses and tubes - still, coolant does come around "the back". However during this exercise air gets pushed out by the arriving coolant and can ONLY escape via the bleed screw or if you have the ET cap off (I use the ET cap off as it is a bigger inlet and outlet and I can see the coolant level in the reservoir). Think about this - if you have coolant going into the engine block through the pin hole in the t-stat housing - how effective is it to have air escaping in the opposite direction thru the same pin hole? (picture of this hole posted below image #3)

This is why it is easier with the thermostat dam open - now there is a bigger throughput for coolant to enter and for air to escape. Not only is the thermostat open but the waterpump is helping push the coolant to the extreme locations of the coolant system - mainly the heater core - where flow is purposely slowed by design to assist in the transfer of heat from coolant to metal by the use of spiral flow rods inside the heater core.

Now you can rely solely on gravity to bleed (BMW instructions) but you can also assist the bleeding process by using the cars ability to flow coolant to get it to those locations and purge the air faster. I suggest you use whatever method you are more comfortable with. Bleeding with the BMW instructions is cumbersome, lengthy and two stage. It was developed that way as they were worried folk would hurt themselves with hot coolant. My concern with it is that if you leave substantial air pockets in an engine you can develop heat spots - this is where coolant is not in contact with the block surface and a crack can form. Don't listen to me- research it yourselves. And in case you didn't know the thermostat (yes even the 97C) starts to open at 80C so you've finished bleeding before the coolant gets anywhere near scalding.

I just took apart an e46 t-stat to show you what I was referring to in regard to the bleed hole in the housing. I also added a couple of images of t-stats for other vehicles where the bleed hole is much bigger but also right on the dam (image #4)

 

Bleeding isn***8217;t real and is a waste of time
I fill up with coolant slowly, drive around the block until it reaches operating temp so the thermostat opens, let the car cool down and fill it again. Keep checking the level the next few days.
No need to even mess with the bleed screw and no need to bleed any air. Why bleed the air anyway? The air comes up to the et, the system bleeds itself.
Btw if you bleed too much air trying to chase bubbles the hoses might collapse when the car is cool

 

Bleeding isn't real and is a waste of time
I fill up with coolant slowly, drive around the block until it reaches operating temp so the thermostat opens, let the car cool down and fill it again. Keep checking the level the next few days.
No need to even mess with the bleed screw and no need to bleed any air. Why bleed the air anyway? The air comes up to the et, the system bleeds itself.
Btw if you bleed too much air trying to chase bubbles the hoses might collapse when the car is cool

A bit time consuming if you're doing this on multiple cars per day in shops, but your right and that's exactly what BMW wanted people to do - and it works about 90% of the time on well maintained cars as our cooling system is designed to purge air into the ET. It does however expose you to the risk of heat spots before top up though. For the other 10% (and climbing with age) that have air locks, or a partially clogged heater valve from the minerals in tap water, or a weak water pump it doesn't work though.

 

Just for fun, here is the BMW coolant bleed steps in the TIS.
newTIS

 

The 100% correct method is linked above.

Just for fun, here are BMW's coolant bleed steps in the TIS.
https://www.newtis.info/tisv2/a/en/...a/en/e46-325ci-cou_200401/repair-manuals/17-cooling/17-00-cooling-check/ANzABPr

Thanks BD. You know I never actually read these BMW instructions but they are the same as what I’ve been saying. The engine needs to be running and the thermostat should be open. So where does the BS come from on this forum about bleeding with the engine off?

3 key points in those linked instructions:

1. Start with a cool engine. Otherwise conditions (input temp sensor values) may prevent the heater valve from opening.

2. Turn on heater and blower

3. Run car until thermostat is open.


What the instructions don’t mention is that stubborn air locks can be pushed out by raising the front end and revving the engine to get the waterpump pushing harder.

Thanks for posting those. BTW. Did you notice the first thing BMW says:

WARNING: Danger of scalding

 

The point is that to correctly bleed this engine the thermostat needs to be open as does the heater valve. Instruction 10 says to start the engine until the thermostat is open. My method just does that while you are still topping it off - no need to drive around the block with air pockets or potential hotspots. No where in the instructions does it say to take car out for a drive - just get the engine up to where the t-stat opens then add more coolant - BMW instructions are designed to prevent scalding. Personally I'd much rather be filling the ET with the cap off, engine running and t-stat open than running it with the cap on then removing it. You're more likely to get scalded that way. Do it however you want.

BTW - I wouldn't call a tablespoon out of the bleed screw significant "spillage" And if you want to avoid even that you can burb it out the ET cap while the t-stat is open and the heater valve open and have no "spillage"

So back to my original point in my first post. Bleeding this engine properly Does mean the engine must be started. Until it does and the thermostat & heater valve have been opened for coolant to circulate the bleeding process is incomplete. Lastly - driving the car before the bleeding process is complete can damage your engine with hotspots caused via airpockets.