How to bleed your cooling system

Okay, so a lot of us here know how to properly bleed/fill our cooling system, but it's a terribly painstaking thing to write the whole procedure out every time someone needs help with it. Here is the right way to fill your cooling system.

Before you go crazy trying to fix an overheating car, make sure that your cooling system is in good shape.

For example:

Is your thermostat working properly?

Is the water pump spinning freely with no lateral motion or grinding noises?

Are your hoses in good shape, not bulging or cracking at the connections?

Is your expansion tank/radiator leaking from a small crack that you can't easily see?

Is your expansion tank cap old and maybe leaking or not letting pressure escape?

These are all eventual problems that our cooling systems suffer from.

If all the components check out and you still have problems, you most likely have air in your cooling system. Plumbers refer to this as "Air-bound."

The same thing happens in home heating systems. If you have baseboard heating in your house then you might have felt the heat on the left side and right side but not in the middle. Air can block the flow of water and cause cold spots. The same thing happens when air is trapped in your engine.
Here is the procedure for filling your cooling system to eliminate the possibility of air causing a blockage, and leading to an overheated (read: destroyed) motor:

Start with the engine cold!

Remove the small black bleed screw from the elbow that connects to the expansion tank.

Remove the coolant filler cap

Turn the ignition on but do not start the engine

Turn the climate control to the highest temperature and put the fan on the lowest setting

Slowly pour coolant into the expansion tank until coolant runs out of the bleed screw hole

keep pouring coolant until you no longer see any air bubbles in the coolant coming out of the bleed screw hole

Replace the bleed screw and check the coolant level in the expansion tank

Replace the expansion tank cap and start the motor

Allow the car to idle until normal operating temperature is reached

Watch carefully to make sure the temperature gauge doesn't rise above 12:00

If the gauge starts to move past 12:00 shut the car off immediately, let it cool and start over

After a few minutes of idling at normal temp it is safe to assume there is a minimal amount of air in the system. Take the car for a quick test drive, carefully watching the temperature. If all is well congrats, you have completed your task, if not, you may still have air in the system. Shut it down, allow it to cool and try again.

Hope this helps out.

Sticky?...

Turn the climate control to the highest temperature and put the fan on the lowest setting

I've seen this mentioned a couple of times, how does this help when adding fluid?

Originally Posted by Darkoz

I've seen this mentioned a couple of times, how does this help when adding fluid?

Heater valve opens hence coolant flows through the heater core too

I see, thanks for clearing that up.

I would like to add the following:
Car should be on level ground.
If the system has been drained, it will take several fillings and some waiting for all the air to come out! Pour coolant in until it runs out the bleed hole. Stop and wait because the level will slowly drop as air rises to the high point and comes out. Keep adding coolant until the level at the bleed screw stops dropping. Now you have a properly bled system! I did not have to add more coolant after the drive.

I would emphasize pouring the coolant in 'SLOWLY'. Doing so will eliminate the need for frequent bleeding of the system.

Bump for more opinions

I think I have air in my system, because of girgling, the temp is fine though...

when the car is cold should the hoses be full of coolant? I can open the bleed screw and squeeze either of the hoses and air comes out, but no fluid. anyone know if that is normal?

This is an excellent post. My low coolant level light keeps coming on then going off. I think when I filled it initially, i didn't bleed the system properly. I have looked a few times to check for leaks and *knock on wood* nothing so far. I'm thinking I can do this and it'll be solved. My temp gauge never goes above normal so that is good. Thanks for the info.

Thanks!

I was gonna comment on the expansion tank thread but didnt get the chance.
Anyways, I think when the procedure is not done correctly, the system gets over-pressurized. Guess what happens... exploding expansion tank. The excess pressure has to go somewhere. Something's gotta give. And that's the poor old expansion tank.

Not all expansion tanks explode so dont blame the expansion tank being of poor quality. Instead THINK of how and why the engine cooling system gets over presssurized in the first place.

If you are having trouble with the expansion tank even accepting enough coolant, then start the engine and briefly rev it to 5000rpms. This forces the air past the air bleed hole in the thermostat; thereby, allowing you to add coolant.

when the engine is cold, isn't the termostat closed, so how can the fluid flow? or does it open once you turn the heater on?

Originally Posted by pstrizz

I think I have air in my system, because of girgling, the temp is fine though...

when the car is cold should the hoses be full of coolant? I can open the bleed screw and squeeze either of the hoses and air comes out, but no fluid. anyone know if that is normal?

You need to fill and bleed the system as described above!

Originally Posted by FatBimmer

Thanks!

I was gonna comment on the expansion tank thread but didnt get the chance.
Anyways, I think when the procedure is not done correctly, the system gets over-pressurized. Guess what happens... exploding expansion tank. The excess pressure has to go somewhere. Something's gotta give. And that's the poor old expansion tank.

Not all expansion tanks explode so dont blame the expansion tank being of poor quality. Instead THINK of how and why the engine cooling system gets over presssurized in the first place.

The cap on the expansion tank is the pressure control device! 13-14 psi normally.

Here's the problem I'm running into. My expansion tank is already full. I open the bleeder screw, there's no water or air coming out. Heater's on high, fan on low, ignition at position 2. Yet, I'm getting to the red every time I drive, faster when AC is on. Then after a while, my AC stops blowing cold air and I have to shut it down. I'm hoping it's just air in there, but I'm not sure how to bleed if the expansion tank show full on the dipstick and no air or water is coming out of the bleed screw. Do I overfill the expansion tank until water comes out the bleed screw??? Or do I run the engine with heat full blast and open the bleeder screw??? A little help please.

Originally Posted by jvidamins

Here's the problem I'm running into. My expansion tank is already full. I open the bleeder screw, there's no water or air coming out. Heater's on high, fan on low, ignition at position 2. Yet, I'm getting to the red every time I drive, faster when AC is on. Then after a while, my AC stops blowing cold air and I have to shut it down. I'm hoping it's just air in there, but I'm not sure how to bleed if the expansion tank show full on the dipstick and no air or water is coming out of the bleed screw. Do I overfill the expansion tank until water comes out the bleed screw??? Or do I run the engine with heat full blast and open the bleeder screw??? A little help please.

You're getting to the red every time I drive, faster with AC on?

JV,

You should not be driving the car and should know, if you've done any cooling work, that when it gets to red you shut it off and get it fixed...towed if necessary. You've done it repeatedly. Stop doing that...you know there's a risk of head gasket/head failure? $1500-2500.

Anyway, my advice is to read a lot of cooling threads, and then, prolly try the instructions exactly above...not sure you've done that...

Also, what were you doing to then need to bleed the system? Maybe that'll give us a hint.

My advice, follow proper bleeding procedure...if that doesn't work, follow the advice of someone really smart who can help you with bleeding while running...

Have you only used OE fluid...miles...other work done....etc?

Doug

Originally Posted by dmax

You're getting to the red every time I drive, faster with AC on?

JV,

You should not be driving the car and should know, if you've done any cooling work, that when it gets to red you shut it off and get it fixed...towed if necessary. You've done it repeatedly. Stop doing that...you know there's a risk of head gasket/head failure? $1500-2500.

Anyway, my advice is to read a lot of cooling threads, and then, prolly try the instructions exactly above...not sure you've done that...

Also, what were you doing to then need to bleed the system? Maybe that'll give us a hint.

My advice, follow proper bleeding procedure...if that doesn't work, follow the advice of someone really smart who can help you with bleeding while running...

Have you only used OE fluid...miles...other work done....etc?

Doug

I only tried bleeding because my temp gauge has been going between the 3/4 mark and the start of red zone the past couple days when driving with AC on. It hasn't actually gone into the red, but right at the edge. Not good either way. The first time I noticed it was when my AC went from good and cold to instantly pushing out lukewarm air. So I shut it off. Today after bleeding using your instructions, I took it for a test drive and temp was fine for the first mile (dead center) with AC on max. Then I accelerated fairly hard and within seconds it was up to the 3/4 mark. I shut the AC off and turned heat to full blast and temp went back down to dead center. AC back on, temp back up. I replaced the coolant and electric aux fan about a month ago with OE. Car has 170k and I just purchased it a couple months ago. Hoses look fine. Expansion tank is fine. No leaking fluid on driveway. Fluid level is full. No weird water pump bearing whining or noises. Is there a way to test and see if it's water pump? How do you know if it's your thermostat?

Originally Posted by jvidamins

I only tried bleeding because my temp gauge has been going between the 3/4 mark and the start of red zone the past couple days when driving with AC on. It hasn't actually gone into the red, but right at the edge. Not good either way. The first time I noticed it was when my AC went from good and cold to instantly pushing out lukewarm air. So I shut it off. Today after bleeding using your instructions, I took it for a test drive and temp was fine for the first mile (dead center) with AC on max. Then I accelerated fairly hard and within seconds it was up to the 3/4 mark. I shut the AC off and turned heat to full blast and temp went back down to dead center. AC back on, temp back up. I replaced the coolant and electric aux fan about a month ago with OE. Car has 170k and I just purchased it a couple months ago. Hoses look fine. Expansion tank is fine. No leaking fluid on driveway. Fluid level is full. No weird water pump bearing whining or noises. Is there a way to test and see if it's water pump? How do you know if it's your thermostat?

Thermostat is prolly tied with water pump as cause, but therm has to be replaced and at that point...don't know cost of WPs, but not having to go into cooling system again...priceless!

Also, not to be mean...but bet that's an original radiator too...$140 buys you a new one...maybe bracket for it...a few hoses, even those that look fine. The heater/engine cooling hoses are original...with 170K...only one is a pitb, and I gave up on it, but will get it next time system is open. Look at your rad really closely...you'll find picks of a failed one right here today.

Just saying, they're machines and cooling system is really important...I make no money saying this, you know, just hate to see bmws stranded or read about cracked heads.

...and add coolant in a.m. when it's cool...and I usually need to add a cup the first morning after a bleeding and maybe an oz or two the day after.

Oh, and you bled following my instructions or Wills, above? I reviewed them and think they're fine, but let it be on Will's head if he forgot something! LOL Anyway, it's Will's thread, so out of courtesy to him, think you ought to follow his instructions...also avail here in some thread from the original TIS...search bleeding/TIS something will likely come up too.

Some of my friends here bleed with engine on...but they know what they're doing...jury is still out on you! LOL Just be careful!

HTH

Doug

Here's is my problem. I replaced expansion tank, water pump, belts, thermostat and one of the hoses. I followed the procedure for bleeding but continue to have problems with the coolant light being on all the time. I replaced the sensor and it didn't make a difference. The car runs fine. Temperature doesn't go over mid point. I just hate having warning lights on. Any advice would be appreciated.

@beauch3

Question:
Is your ET generic or BMW brand?
Because some generic tanks have an slight issue of the magnet within that's not lined up properly causing it to trigger the low coolant light.