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View Full Version : How to properly bleed cooling system


wolferj
09-03-2009, 11:34 PM
There's a lot more to it than just removing the bleed screw and filling the expansion tank. This is why people have to go back and rebleed over and over.

Start by parking on an incline so the nose of the vehicle is angled upward. Air bubbles travel up. With a cool/running engine, turn the heater on full blast. By full blast, I mean turn the temp knob on the HVAC panel to full red and turn the fan all the way to the highest setting. This will allow coolant to circulate through the heater core. Now, pop the hood and remove the radiator fill cap and bleed screw. Slowly add coolant/water to the radiator expansion tank. Continue to fill until you see coolant exiting the bleed hole. You can assist the air bubbles by tapping on the top of the radiator and massaging the radiator hoses. Once you see a steady stream of coolant with no bubbles flowing out of the bleed hole, replace the bleed screw and fill cap. Drive around the block a few times, park on the same incline, let the engine cool and repeat the process 3 or 4 times.

Thanks!

713bmw318ti
11-23-2009, 01:47 AM
Man my heater was not working for 3 years and I bled the cooling system today. All i got to say is the heater blows hot!!!!

pdxmotorhead
11-24-2009, 07:08 AM
Redline water wetter. It helps! The chemical breaks the surface tension of the coolant and helps air pass through the system.

Dave

dgroebl
12-20-2009, 09:07 PM
So what if your radiator is already filled to the cold line? In order to get coolant from my bleed screw I have to fill the over flow tank higher than the cold line on the tank. I have to almost completely top off the radiator in fact to get coolant from the bleed screw. Do I need to worry about over filling my cooling system?

cooljess76
12-20-2009, 09:15 PM
So what if your radiator is already filled to the cold line? In order to get coolant from my bleed screw I have to fill the over flow tank higher than the cold line on the tank. I have to almost completely top off the radiator in fact to get coolant from the bleed screw. Do I need to worry about over filling my cooling system?

Nope, the fill cap has a built in relief, so the system will not/should not overpressurize.

dgroebl
12-20-2009, 09:26 PM
So then should I eventually siphon some out to get it back down to the cold mark? Or just don't worry about it because it will take care of it's self?

cooljess76
12-20-2009, 09:38 PM
it'll level itself out once you drive the vehicle.

dgroebl
12-20-2009, 10:14 PM
Thanks. So that's basically what I did last weekend. Seamed like the heater was maybe only 80% of what it should be though. So now I'm doing it again. Its been about 20 minutes, heaters nice and hot, probably got about a quart of coolant on the floor, but the bubbles just keep trickling out! Every 20 seconds or so there's a few more. I'm starting to think head gasket! :eek:

bmvw
12-21-2009, 01:25 AM
Why is there so much drama with the BMW cooling system. I have a 300,000 mile Toyota and I think I only checked the coolant once. Yet BMW (& I hear Benz also) one little plastic part breaks and $5000 engine.

dgroebl
12-21-2009, 06:20 PM
I think cars always reflect the culture that they came from:

Japan = Memoirs of a Geisha vs. Germany = Femdom

pdxmotorhead
12-21-2009, 06:23 PM
Interestingly enough, I've drained my TI several times to do work never jacked it up tilted it or any thing. Just filled it back up opened the bleed screw and it purges fine....
I always use water wetter.

I've probably just cursed myself... :)

Dave

William
04-06-2010, 02:30 PM
I flushed the cooling system and went through all the procedures listed above. My heat is so hot it will run you out of the car. My problem starts on day 2. After the car sits overnight there is tons of pressure built up. Car is hesistant to start. Remove bleed screw and cap. Pressure is relieved and car starts right up. Not quite sure what is going on, and I know I may have left out some details, but I need some direction.

cooljess76
04-06-2010, 05:29 PM
I flushed the cooling system and went through all the procedures listed above. My heat is so hot it will run you out of the car. My problem starts on day 2. After the car sits overnight there is tons of pressure built up. Car is hesistant to start. Remove bleed screw and cap. Pressure is relieved and car starts right up. Not quite sure what is going on, and I know I may have left out some details, but I need some direction.The radiator cap is supposed to have a built-in relief @ a certain pressure. I think it was 15-19psi, but don't quote me on that. I can't remember what it is off the top of my head, but excessive pressure is bad. It sounds like your expansion tank is not relieving itself, you should make sure you have the correct radiator cap. Might also be a good idea to do a cylinder leakdown test as cooling system overpressurization can be caused by a minor head gasket leak.

sleighty
04-07-2010, 07:36 PM
i fixed one of the plastic cooling pipes a few months back, refilled and bled the system with no problems i get a nice hot heater when required and the engine sits at the middle of the temp gauge. However in the radiator reservoir its about half way full, if i fill it to the top and do around a fortnights driving and recheck its gone down to half full again. Could i still have a leak? Or is this level normal? Ive never wanted to let it get any lower than half full so im not sure if i goes any lower

cooljess76
04-07-2010, 08:16 PM
i fixed one of the plastic cooling pipes a few months back, refilled and bled the system with no problems i get a nice hot heater when required and the engine sits at the middle of the temp gauge. However in the radiator reservoir its about half way full, if i fill it to the top and do around a fortnights driving and recheck its gone down to half full again. Could i still have a leak? Or is this level normal? Ive never wanted to let it get any lower than half full so im not sure if i goes any lowerYou might still have a leak or perhaps a cracked radiator/expansion tank. The best way to find out is to use a radiator pressure test kit, pressurize the system to about 10psi and listen for leaks. Another thing, CirrusSR22 noticed that one of the plastic cooling pipes had a defective flange on it that wouldn't allow it to seal properly. Check this thread for more info on that:
http://www.318ti.org/forum/showthread.php?t=18066

ChItalian1027
04-16-2010, 11:45 PM
Thanks James and Jess! Jess or James if you guys could answer this.

Is the bleed screw at the top or the bottom of the radiator or is it on the expansion tank?

spidertri
04-17-2010, 12:12 AM
Bleed screw is at the top right next to the expansion tank fill cap.

cooljess76
04-17-2010, 12:16 AM
yep, plastic screw next to the cap. You could use a quarter to tighten/loosen it. Don't over-tighten it as I've heard of people snapping them off:wink:

ChItalian1027
04-17-2010, 12:33 AM
Ok, thanks guys!! time to bleed my system

mugger7714
04-25-2010, 08:51 AM
ok i tried this and i did it 3 times as directed and now my car overheats it never over heat before what should i do ?

R111S
05-06-2010, 01:55 AM
It really does work. I just replaced my leaking Expansion Tank. It was leaking around the lower O-Ring Seal.

Notes for my Log File:

04MAY2010 – The new parts from Pelican arrived today. I greased the upper and lower Gasket Rings, w/Silicone Grease, of the new “Kühlerausgleichsbehälter” or in English “Expansion Tank” first. After cleaning the sealing surfaces of the mating holes, I installed it – it took allot of downward pressure to make it go into the holes.

I parked the car on the driveway where it slopes the steepest so that the nose of the car was high. I removed the Expansion Tank Cap and the Bleed Screw to begin bleeding the air out of the system. With the engine running, I filled up the Expansion Tank with a 50/50 mix of BMW Coolant and Water till coolant overflowed the bleed screw hole (close to the “Kalt” line).

A couple of times, when the bubbles stopped, I put the bleed screw back in, revved the engine once, and then took it back out and topped up again to get the overflow and bubbles going again.

I had the Heater on Full the whole time and it slowly went from barely warm to really hot. The bubble bleeding process took ~15 minutes. A short test drive revealed the Temperature Indicator held steady at the straight up position and no leaks were noted - and the Heater puts out lots of heat! The following morning I topped up the Expansion Tank to the “Kalt” mark.

Post Script - 24NOV2010 and ~10K Miles later:
It's been below freezing overnight the last few days and the heater works great. No problems with the cooling system since the work noted above was perfomed. A ~2300 Mile trip to the Gulf Coast last month went well too.

blndweasel
06-07-2010, 08:30 PM
Just a note on this -- the Bentley manual has this procedure outlined, and says you can just turn the key to the ON position, without starting the car. Then turn the heater controls to full HOT. set your fan to "1".

Tried this, and it works just fine. Not that filling the coolant with the engine running should be any concern anyways. It takes a little longer to bleed the air out without the engine running, but works just fine.

tbw

cooljess76
06-07-2010, 09:16 PM
Just a note on this -- the Bentley manual has this procedure outlined, and says you can just turn the key to the ON position, without starting the car. Then turn the heater controls to full HOT. set your fan to "1".

Tried this, and it works just fine. Not that filling the coolant with the engine running should be any concern anyways. It takes a little longer to bleed the air out without the engine running, but works just fine.

tbwHere's why the Bentley manual is screwed up. If the engine is not running, the water pump is not spinning. If the water pump is not spinning, coolant isn't circulating through the radiator, engine and heater core. The reason you turn the heater on full blast is beacause it opens the valve to the heater core and lets the coolant circulate through it just in case there's air trapped in there as well. The fan setting has nothing to do with the flow rate of the coolant, only the blower itself which blows air across the top of the heater core and into the cabin. I tell people to turn it on full blast so they can feel the heat coming out of the vents easier. The whole idea of bleeding the system is to get the air to escape. The water pump is driven by the belt. If the belt isn't turning the water pump, how is the coolant going to circulate? It can't. Simple mechanics.

The Bentley is full of typos and misinformation and this is just another one of them. It almost caused me to seriously damage my engine when I was replacing the timing cover gasket and setting the timing. Never trust the Bentley 100%. It's an alright source of info, but I always verify things before taking the Beltley's word.

THE ENGINE MUST BE RUNNING TO PROPERLY BLEED THE COOLING SYSTEM.

blndweasel
06-08-2010, 12:33 AM
The water pump is driven by the belt. If the belt isn't turning the water pump, how is the coolant going to circulate? It can't. Simple mechanics.

Jesse, I'm not trying to contest any information you're providing here, I'm just contributing my own observations.

The coolant doesn't have to be circulating for air to escape, because the air rises and is released through the bleeder valve when it is open. By adding coolant to the expansion tank, with the vehicle on an incline (the one thing they definitely DON'T mention in Bentley), the coolant you add to the top of the expansion tank is at a higher point than anything else in the system. Gravity does the rest.

Now, it takes a goddamn long time, because the only way for air inside the engine circuit to escape the system to reach the bleeder screw, is passing through the BB-check valve in the thermostat (smallest point of constriction and only way for air to escape with T-stat closed), but eventually, you get coolant coming out of the bleeder valve as described. I too, thought the Bentley manual was wrong, I went back to re-read it, and by the time I came back and looked at the expansion tank, a half inch worth of coolant had filled into the system. It just takes a really really long time.

Yes, turning the fan on inside the vehicle probably doesn't do anything. I thought "just in case", since without knowing the circuitry of the heater valve, I thought it might stay closed if the fan is set to "0". Since the heater valve is electronically controlled, I did this just in case, and mentioned it just because.

In the end, it takes probably 15 minutes of VERY SLOWLY adding coolant to the expansion tank until tiny bubbles of water and air, then eventually a constant stream of coolant water is coming out of the bleeder screw. The expansion tank will be full to the brim, but this is fine because once the engine warms up, it will take whatever it needs of that excess coolant, and burp off the rest. By the time you fully heat cycle the engine, the coolant should be back at the "kalt" mark.

Do it my way, do it your way, it doesn't matter, just make sure you properly bleed your coolant system before operating the engine.

tbw

The other thing to mention is that perhaps my scenario worked because I had just installed a fully overhauled M44 engine, and physically inspected every single cooling system component. New T-stat. New waterpump. New fittings. In an older engine, it's quite likely you might have mineral deposits clogging your BB-check valve, or some other small passage in the circuit, which would make this whole process impossible. You would have to bring the engine to temp, and let the T-stat open in order to bleed the air out. Or it might take several heat cycles for the air to eventually work its way out. Every engine is different in this respect, and the older and less maintained an engine is, the less likely it will behave like a fresh-from-the-factory M44, which is what Bentley based all of their procedures on.

just my $0.02!

chudzikb
06-08-2010, 04:21 AM
Just did this, put the heater on high, put the car half way up the curb to get the nose in the air, opened the bleeder screw and let it burp. Was easier than my 97 328i, lots easier, got it done first time. Did it 2X after cooling down, did it again. No issues.

blndweasel
06-08-2010, 05:53 PM
I went back and checked my levels again several times yesterday, burped it again with the engine hot, burped it again with the engine cold. No air bubbles. Basically my coolant had dropped about 1/2" from the cold mark since I originally did the bleeding procedure with the engine off last Monday. Approx 10 heat cycles have occurred since.

There is of course a certain volume of space inside the engine block which resides above the BB check valve in the thermostat. There is probably also a certain volume of space in the heater core which resides above the control valve (although I have never serviced the heater core, and don't know if it's oriented/located at any point above the valve). Both of these scenarios would represent air still trapped in the system after a cold bleed procedure.

With the cold bleeding procedure, what you end up with is an expansion tank which is filled to the brim. Presumably what happens is, after cold bleeding, the first time the T-stat opens with the water pump circulating coolant, the remaining air pockets inside the block fill with coolant, and it siphons from that excess volume in the expansion tank. furthermore, after the system pressurizes itself for the first time, upon cooling, the reducing volume of fluid (PV=nRT) will effectively suck up more of that excess expansion tank fluid. Several heat cycles would eventually work out any remaining smaller bubbles, and then you find yourself with an expansion tank which is either back to the normal cold marking, or perhaps slightly lower.

My personal opinion (and I know that others will argue against this) is that the cold bleeding procedure detailed in the Bentley manual WORKS if you are extremely patient while filling due to the restriction of air passing through the BB check valve, and you follow up after several heat cycles of the engine to verify coolant levels.

Also note -- I would only feel confident stating this opinion for an M44 cooling system which is in verifiably perfect condition -- one which is very close to factory specifications (e.g. low miles, or recently replaced service items, no corrosion or calcification / chlorination deposit buildup in the circuit).

That said, there is no reason NOT to do the same procedure with the engine running, as stated in the KB article. I've performed this process as well, and can verify it works also.

What I would suggest is that BOTH procedures are only complete after the engine has fully heat cycled, and the T-stat has opened and released any remaining trapped air from the engine coolant circuit. Each successive heat cycle post-bleed will remove smaller and smaller amounts of air trapped in the system. In my case with the cold bleed procedure, it seems to have represented about 1/2" worth of coolant in the expansion tank.

The Bentley process is really only intended to ensure that enough coolant is in the system so that on initial startup, you won't suck the expansion tank dry and end up with excessive air pockets potentially preventing circulation of coolant in the block.

Again, exhaustively, whichever process you follow, you *must* bleed your coolant circuit any time you service any items in this group. Furthermore, you *must* follow up after several heat cycles to top off the system.

tbw

mohaughn
06-08-2010, 06:53 PM
One thing that my Ti does that I've not seen mentioned in any of the cooling burp discussions is that the electronic heater valve will stick shut sometimes. I live in Florida and never use the heat in the car, so not something that I notice unless I'm trying to burp the system. I have to take a really long screwdriver, turn it around backwards and tap on the electronic valve sometimes to get it to open and then let the system flush.

Sometimes I can get it super easy and less than 5 minutes. The last time I replaced hoses I had to get one of my mechanic buddies to burp it for me at the track because I had been trying for 45 minutes and couldn't get it to burp...

19742002tii
08-05-2010, 04:37 AM
Dont start the car with the plug removed, hah hah. That said, starting to get heat. Hard to tell when it's 100 outside:cool:

btbiii
08-29-2010, 08:42 PM
Where is the bleeder for the cooling system? Is it the screw next to radiator cap? Do I just remove the plastic plug?

tiFreak
08-30-2010, 01:37 AM
Where is the bleeder for the cooling system? Is it the screw next to radiator cap? Do I just remove the plastic plug?

that should be it, it has the German word on it for bleeder I believe

MusicalRich
11-24-2010, 01:04 AM
Why is there so much drama with the BMW cooling system. I have a 300,000 mile Toyota and I think I only checked the coolant once. Yet BMW (& I hear Benz also) one little plastic part breaks and $5000 engine.

What I have found, is a lot of people think these are little race cars and neglect basic PM( prevtative Maintenance). Also because of that, some owners just don't take the time and when you find one, it's been abused.

antny
10-08-2011, 12:49 AM
Ok guys I am going to bump this because I am about lost in my troubles. I have bled the system more times than I can count now following these instructions to the T. I have replaced every single part and hose to the cooling system so everything is new. MY car is still getting hot sitting at idle and thats with the fan wired to run all the time. Headgasket is fine, no smoke and the plugs are bone dry. NO coolant leaks at all anywhere in the system. Could it be a faulty temp sender? Wiring from the sender bad? This is a motor that came from a running car with no cooling issues before I put it in. Any Ideas or thoughts? I really have bled the system over 20 times and even bypassed the heater core to ensure there wasnt any chance for any air pockets in that system. Thanks, I am just at a loss here.