[alddiem415]

I will be replacing the expansion tank on my 11 335i xdrive.

Do i need to bleed the system?

[NinetyEight740]

Absolutely, any time you lose any coolant you need to bleed the system.

[ewicky]

Our cooling systems are self bleeding. Just keep adding coolant until it stops taking it. There's no need to crack a bleeding screw open or anything like that.

[FlyingBuckeye3]

Yes, you'll need to bleed the system. Be ready for coolant to pour out of the lower hose when you disconnect it, assuming you still have a fair amount of coolant left in the car. After replacing my tank, I filled the system back to the max level in the expansion tank, bled the system, and checked the level again, filling with more coolant as necessary.

Do you know what caused the need to replace the expansion tank? For me, it signaled my water pump was going bad.

[N52bigblock]

Yes definitely bleed it. They have a bleeding procedure and bleed screw for a very good reason.

[ewicky]

Originally Posted by neilj35

Yes definitely bleed it. They have a bleeding procedure and bleed screw for a very good reason.

The reason is so that dealers can send people on their way without the customer ever having to top off coolant.

If you are a DIYer and don't mind pouring your coolant, there is no need to bleed. After a few moments of observation, anyone who has passed middle school physics could understand how it's self bleeding, the bleeding screw does essentially nothing because of its location, and you just need to drive and keep topping off until it's full.

Now, if you really wanted to be fancy and ensure there are no air bubbles, you should... also not bleed the system. You would vacuum the system. That's because no bleed, whether thru a traditional bleed screw, our useless bleed screw, or self bleeding, is perfect. But a vacuum down to as-near-as-can-be absolute vacuum will definitely insure the system is free of bubbles.

[N52bigblock]

Originally Posted by ewicky

The reason is so that dealers can send people on their way without the customer ever having to top off coolant.

If you are a DIYer and don't mind pouring your coolant, there is no need to bleed. After a few moments of observation, anyone who has passed middle school physics could understand how it's self bleeding, the bleeding screw does essentially nothing because of its location, and you just need to drive and keep topping off until it's full.

Now, if you really wanted to be fancy and ensure there are no air bubbles, you should... also not bleed the system. You would vacuum the system. That's because no bleed, whether thru a traditional bleed screw, our useless bleed screw, or self bleeding, is perfect. But a vacuum down to as-near-as-can-be absolute vacuum will definitely insure the system is free of bubbles.

Ok then you stick to your theory and I'll stick to mine.

[mweisdorfer]

You should :

1) crack the bleeder screw when filling the new expansion tank.

2) Close the screw.

3) Put the cap on tight.

4) Put a battery charger on it, set to maintenance.

5) put the key in & turn the your heat all the way up & set to level one.

6) press the gas pedal down for 10 Seconds until you hear the water pump kick on & let it run for 14 min.

7) when it's done, check the level of the expansion tank. If you have to add coolant repeat steps 1-6 & you are done !

You might say it's overkill, but better safe than sorry !

[banglenot]

I've got to speak up because the "no bleeding needed" statement is simply wrong, per newtis. If you're new to BMW's you may believe that the system is self bleeding. It is not.

Like the OP's '11 335, these use an electric coolant pump and an electronic bleeding procedure that is started as the expansion tank is being filled. It takes about 12 minutes and forces all the air out of the system. The Pierburg and VDO electronic pumps used in them are expensive ($300+) and all the procedures to bleed the system should be used.

Here's the procedure on a typical N52: https://www.newtis.info/tisv2/a/en/e...-drive/ElXYxd2

Newtis has a procedure related to bleed/fill with vacuum filling unit, but still requires the above electronic bleeding as well.

The best procedure I've used has a tool like a funnel that screws onto the expansion tank. It allows coolant to be poured in, and forced up out of the tank as bubbles are released, without making a mess. Doesn't require a bleed screw to be opened.

[N52bigblock]

Originally Posted by mweisdorfer

You should :

1) crack the bleeder screw when filling the new expansion tank.

2) Close the screw.

3) Put the cap on tight.

4) Put a battery charger on it, set to maintenance.

5) put the key in & turn the your heat all the way up & set to level one.

6) press the gas pedal down for 10 Seconds until you hear the water pump kick on & let it run for 14 min.

7) when it's done, check the level of the expansion tank. If you have to add coolant repeat steps 1-6 & you are done !

You might say it's overkill, but better safe than sorry !

Exactly.

[ewicky]

Originally Posted by banglenot

I've got to speak up because the "no bleeding needed" statement is simply wrong, per newtis. If you're new to BMW's you may believe that the system is self bleeding. It is not.

Indeed, newtis is procedures originally intended for dealers. And as I mentioned, dealers will bleed so they don't have to send customers home with a jug of coolant.

The fact that, even according to newtis, the electric pump procedure is done with the "bleed screw" closed makes the system, by definition, self bleeding. That's literally why there are two hoses going to the expansion tank. It isn't rocket science, people. It's the way it's designed.

EDIT: about "new" people; it is likely the reverse of your suggestion. DIYers who have been around BMWs for decades have a much higher chance of understanding how BMW designs their cooling systems. At least one could hope.

[N52bigblock]

Originally Posted by ewicky

Indeed, newtis is procedures originally intended for dealers. And as I mentioned, dealers will bleed so they don't have to send customers home with a jug of coolant.

The fact that, even according to newtis, the electric pump procedure is done with the "bleed screw" closed makes the system, by definition, self bleeding. That's literally why there are two hoses going to the expansion tank. It isn't rocket science, people. It's the way it's designed.

EDIT: about "new" people; it is likely the reverse of your suggestion. DIYers who have been around BMWs for decades have a much higher chance of understanding how BMW designs their cooling systems. At least one could hope.

If the "self bleed" method works for you then that's great. But as a mechanic of 26 years i honestly think you will come unstuck using that method sooner or later. I've seen DIY disasters on numerous occasions. I sincerely hope it keeps working for you, but to others who read this, experience tells me this method is very risky. I do not recommend it at all. Proper bleed procedure is a must. That's just my opinion. Pretty sure 99% of mechanics would either use the bleed procedure and or vacuum.

[Efthreeoh]

Originally Posted by ewicky

The reason is so that dealers can send people on their way without the customer ever having to top off coolant.

If you are a DIYer and don't mind pouring your coolant, there is no need to bleed. After a few moments of observation, anyone who has passed middle school physics could understand how it's self bleeding, the bleeding screw does essentially nothing because of its location, and you just need to drive and keep topping off until it's full.

Now, if you really wanted to be fancy and ensure there are no air bubbles, you should... also not bleed the system. You would vacuum the system. That's because no bleed, whether thru a traditional bleed screw, our useless bleed screw, or self bleeding, is perfect. But a vacuum down to as-near-as-can-be absolute vacuum will definitely insure the system is free of bubbles.

I have to chime in... You are completely wrong. I've been wrenching on BMWs for over 30 years, and have worked on BMW cooling systems back to the E21. The N52/54/55, with an electric cooling pump, uses a cold-bleed procedure. First off calling the tank an "expansion" tank is misleading. The tank is not a tradditional expansion tank with a rubber hose that allows coolant from the system to expand into a holding tank when the radiator cap pressure valve opens. The E9X tank is a coolant reservoir. It's pressurized, and feeds coolant to the cooling system. The E9X radiator has no storage capacity. The tank has two lines. The line that feeds into the tank where the bleed screw is is a return line from the top radiator hose. When the system is bled, that small-diameter line allows the air trapped in the engineblock, and more importantly the cylinderhead, to bleed out of the cooling system as the engine fills up with coolant from the bottom. That's why the line is at the top of the system and why the bleed screw needs to be open when refilling to cooling system after a full drain. Keeping the bleed screw closed prevents the air trapped in the block and head from escaping the system. As the engine fills, the air can't force it's way out of the coolant reservoir through the fill neck. The bleed screw gives the air the shortest and easiest path to escape the system.

If the system were a true vacuum, the pump would not be able to spin. The cooling system needs air space in it to allow for coolant expansion. The air space is in the coolant reservoir, which is why the tank is at the highest point in the cooling system.

[ewicky]

Originally Posted by Efthreeoh

I have to chime in... Dude, you are completely wrong. I've been wrenching on BMWs for over 30 years, and have worked on BMW cooling systems back to the E21. The N52/54/55, with an electric cooling pump, uses a cold-bleed procedure. First off calling the tank an "expansion" tank is misleading. The tank is not a tradditional expansion tank with a rubber hose that allows coolant from the system to expand into a holding tank when thevradiator cap pressure valve opens. The E9X tank is a coolant reservoir. It's pressurized, and feeds coolant to the cooling system. The E9X radiator has no storage capacity. The tank has two lines. The line that feeds into the tank where the bleed screw is is a return line from the top radiator hose.

yup yup yup. I find traditional expansion tanks to be inferior to the self-bleed reservoir design.

Originally Posted by Efthreeoh

When the system is bled, that small-diameter line allows the air trapped in the engine block, and more importantly the cylinder head, to bleed out of the cooling system as the engine fills up with coolant from the bottom.

yup, literally how the system self bleeds. A two hose reservoir system, with the smaller top one acting as an air-bubble-return-line until the system has fully bled itself. And the bottom, larger hose fills up the engine from the bottom. I'm glad we are in agreement, not sure how that means I'm "completely wrong".

Originally Posted by Efthreeoh

That's why the line is at the top of the system and why the bleed screw needs to be open when refilling to cooling system after a full drain. Keeping the bleed screw closed prevents the air trapped in the block and head from escaping the system. As the engine fills, the air can't force it's way out of the coolant reservoir through the fill neck. The bleed screw gives the air the shortest and easiest path to escape the system.

I encourage you to lookup the scientific functional definition of "displacement" because that's not how physics works. Also, the bleed screw isn't on the block nor head, so it has no control over air being trapped in those locations. That is why I mentioned previously the silly location for our "bleed screw". Which, by the way, BMW newtis refers to as a vent screw not a bleed screw. I can only speculate why.

Originally Posted by Efthreeoh

If the system were a true vacuum, the pump would not be able to spin.

Pump can spin in a vacuum no problem, so I'm not sure what you mean by this. Obviously when I mentioned vacuuming the system, I mean temporary as a superior alternative to attempting to "bleed" it. You wouldn't want to seal the system up vacuumed (somehow) when the car/pump was running anyways because the coolant would boil too easily, but I don't think that's what you really meant because that would be ridiculous.

Originally Posted by Efthreeoh

The cooling system needs air space in it to allow for coolant expansion. The air space is in the coolant reservoir, which is why the tank is at the highest point in the cooling system.

yup yup yup.


Look, I'm not trying to be a donkey's rear end here. And I recognize several members' names as being terribly helpful all over these forums. Respect is due for that. But to answer this thread's particular question: our cars don't have a traditional cooling system design that would need bleeding. And I feel like people who understand gravity and displacement can see how, because of the way BMW designed it, there's no way the system could possibility be bled out of the bleed screw.

[ewicky]

Originally Posted by neilj35

If the "self bleed" method works for you then that's great. But as a mechanic of 26 years i honestly think you will come unstuck using that method sooner or later. I've seen DIY disasters on numerous occasions. I sincerely hope it keeps working for you, but to others who read this, experience tells me this method is very risky. I do not recommend it at all. Proper bleed procedure is a must. That's just my opinion. Pretty sure 99% of mechanics would either use the bleed procedure and or vacuum.

If following BMW procedures is a must, independent thought is forbidden, and anything else is "risky," then I hope everyone here is using runflat tires and changes all four with brand new ones every time they have a puncture. I also hope nobody has ever tuned their car with anything other than Dinan.

I joke. On a more serious note, you have voiced your opinion and so have I. Anyone reading is hopefully capable of critically thinking and can make their own decision, and not just blindly follow procedures that weren't meant for them, just for the heck of it.

[Efthreeoh]

Originally Posted by ewicky

yup yup yup. I find traditional expansion tanks to be inferior to the self-bleed reservoir design.yup, literally how the system self bleeds. A two hose reservoir system, with the smaller top one acting as an air-bubble-return-line until the system has fully bled itself. And the bottom, larger hose fills up the engine from the bottom. I'm glad we are in agreement, not sure how that means I'm "completely wrong".I encourage you to lookup the scientific functional definition of "displacement" because that's not how physics works. Also, the bleed screw isn't on the block nor head, so it has no control over air being trapped in those locations. That is why I mentioned previously the silly location for our "bleed screw". Which, by the way, BMW newtis refers to as a vent screw not a bleed screw. I can only speculate why.Pump can spin in a vacuum no problem, so I'm not sure what you mean by this. Obviously when I mentioned vacuuming the system, I mean temporary as a superior alternative to attempting to "bleed" it. You wouldn't want to seal the system up vacuumed (somehow) when the car/pump was running anyways because the coolant would boil too easily, but I don't think that's what you really meant because that would be ridiculous.yup yup yup.


Look, I'm not trying to be a donkey's rear end here. And I recognize several members' names as being terribly helpful all over these forums. Respect is due for that. But to answer this thread's particular question: our cars don't have a traditional cooling system design that would need bleeding. And I feel like people who understand gravity and displacement can see how, because of the way BMW designed it, there's no way the system could possibility be bled out of the bleed screw.

I'm sorry, but I think you misunderstand the cooling system. I described in my last post exactly the purpose of the bleed screw. Every BMW I've owned has a bleed screw at the top of the cooling system to allow air trapped in the engine to escape the system as the engine fills with coolant. If you look closely at the E9X cooling system design, the small return line that mounts to the elbow on the top radiator hose is the pathway for trapped air to escape the system through the bleed screw. The bleed screw is in place exactly at the location the small return line enters at the top corner of the reservoir tank. If the bleed screw is not open the air can't find another way out of the system since the reservoir design will not allow it.

And TBH what automotive cooling system is not self bleeding? All of them are design to bleed off pressure. I and others here that wrench on these cars really just don't understand why you think you have better bleeding technique than the manufacturer who actually designed the system does.

[N52bigblock]

Originally Posted by ewicky

If following BMW procedures is a must, independent thought is forbidden, and anything else is "risky," then I hope everyone here is using runflat tires and changes all four with brand new ones every time they have a puncture. I also hope nobody has ever tuned their car with anything other than Dinan.

I joke. On a more serious note, you have voiced your opinion and so have I. Anyone reading is hopefully capable of critically thinking and can make their own decision, and not just blindly follow procedures that weren't meant for them, just for the heck of it.

Like i said before, i have seen many DIY disasters over the years, the last of which was a Mini owner who changed his thermostat and just refilled the cooling system without using the bleed screw and "was sure he got all the air out" The end result was him overheating the engine and the valve seats falling out and destroying the engine. If you think you know better than everybody else on this forum and the BMW Engineers who designed the system then good luck to you. I still think you will come unstuck with your method sooner or later. Good luck. That's all I'm saying on this subject. I'm out.

[Efthreeoh]

Originally Posted by ewicky

yup yup yup. I find traditional expansion tanks to be inferior to the self-bleed reservoir design.yup, literally how the system self bleeds. A two hose reservoir system, with the smaller top one acting as an air-bubble-return-line until the system has fully bled itself. And the bottom, larger hose fills up the engine from the bottom. I'm glad we are in agreement, not sure how that means I'm "completely wrong".I encourage you to lookup the scientific functional definition of "displacement" because that's not how physics works. Also, the bleed screw isn't on the block nor head, so it has no control over air being trapped in those locations. That is why I mentioned previously the silly location for our "bleed screw". Which, by the way, BMW newtis refers to as a vent screw not a bleed screw. I can only speculate why.Pump can spin in a vacuum no problem, so I'm not sure what you mean by this. Obviously when I mentioned vacuuming the system, I mean temporary as a superior alternative to attempting to "bleed" it. You wouldn't want to seal the system up vacuumed (somehow) when the car/pump was running anyways because the coolant would boil too easily, but I don't think that's what you really meant because that would be ridiculous.yup yup yup.


Look, I'm not trying to be a donkey's rear end here. And I recognize several members' names as being terribly helpful all over these forums. Respect is due for that. But to answer this thread's particular question: our cars don't have a traditional cooling system design that would need bleeding. And I feel like people who understand gravity and displacement can see how, because of the way BMW designed it, there's no way the system could possibility be bled out of the bleed screw.

I'll not argue who has more college credits in Physics....

But I will argue the bleed screw doesn't need to be on the engine cylinderhead; it needs to be at the highest point in the cooling system, which is where the air will collect when pushed from the block as the liquid coolant displaces the air within the block. So the bleed screw is on the cooling system reservoir, which is higher than the top of the cylinderhead and a few inches above any water jacket inside the head.

Not sure you understand what vacuum means in terms of physics.

You are completely wrong because you state and argue that the bleed screw is useless and advise not to follow BMW's bleeding procedure. In fact when one reviews BMW's literature regarding the design of the N52 engine and its use of an electric cooling pump, it states BECAUSE the system uses an electric cooling pump "a special filling and bleeding procedure must be implemented for servicing." Pg. 58 of the New Generation 6 Cylinder N52.

[Wolf 335]

Just a comment...Every reputable independent bmw shop in my area claims that the system is self bleeding as well. And these are the guys that used to work for bmw before they left and opened their own shops.

[gbalthrop]

Originally Posted by alddiem415

I will be replacing the expansion tank on my 11 335i xdrive. Do i need to bleed the system?

Originally Posted by Wolf 335

Just a comment...Every reputable independent bmw shop in my area claims that the system is self bleeding as well. And these are the guys that used to work for bmw before they left and opened their own shops.

Problem with the replies to this thread is that it appears NO ONE has answered the OP's question. Actually the OP SHOULD have stated (1) WHY he was replacing the Reservoir, and (2) How long it has been since the coolant was drained and refilled.

There are multiple reports on the forums of reservoirs bursting due to too much coolant in the system with NO room for expansion of the coolant as it warms, and possibly a failed pressure release mechanism. Obviously, if the reservoir failed in such a manner that plastic shrapnel was introduced into the system, care should be taken to make sure that has NOT gotten into the pump. So OLD Reservoir failure may cause pump failure, OR be the symptom of another issue which MAY cause failure of the NEW Reservoir.

If OP is replacing the Old Reservoir simply due to a leak, his question MAY be: Is there a way to replace the reservoir, so that I don't have to Bleed the system? The answer is YES. Simply clamp off the larger hose BELOW the reservoir (to prevent coolant from flowing UP, out of the hose fitting when disconnected from the old reservoir), and have the replacement reservoir ready to attach as soon as you remove the old. THAT will prevent loss of more than about an ounce of coolant if done correctly, and if the fitting separates without issue. I'm NOT familiar with the N55 Engine, but if the Reservoir is basically the same as N52 with two fittings, that should work.

That said, when you have an electric coolant pump and a battery charger, WHY take any chances that there is an air pocket in the head that, as Neil suggests, may cause local overheating and damage a valve seat or other issue from overheat. BEFORE you start the engine, you can make sure that ALL the air is out by running the bleed procedure, topping off, and running it again. You do NOT have to "babysit" the bleed procedure, so what's the rush? If there is ANY doubt about cooling system history, or how much air got into the system, (1) DRAIN the old coolant, and then (2) Refill & BLEED the system according to this TIS procedure, SPECIFICALLY for N55:
https://www.newtis.info/tisv2/a/en/e...check/D84yFYBu

QUESTION:
On US models which do NOT have a "Water Valve" or "Auxiliary Pump" located at the base of the left Strut Tower, is there any reasons to do Step 3 of the procedure linked above: "Set heater to maximum temperature and turn blower down to lowest speed"?

George

[Efthreeoh]

Originally Posted by Wolf 335

Just a comment...Every reputable independent bmw shop in my area claims that the system is self bleeding as well. And these are the guys that used to work for bmw before they left and opened their own shops.

Okay, but what modern automobile doesn't have a self-bleeding cooling system? If the cooling system has a filling cap on the system that has a pressure valve built into it, then it's self bleeding. It's not like the E9X has some magic self-bleeding cooling system different from other BMWs, or even other brands. All four of my BMWs use the same bleed screw on their cooling systems. Two cars have electric pumps and two have belt-driven pumps. The bleeding procedure is slightly different for each car, but all procedures call for slowly filling the cooling system with the bleed screw open and stop filling once a bubble-free stream of coolant is flowing from the bleed screw.

All cooling systems can trap air inside the cylinderhead, which is problematic, because the head can rapidly overheat without indication from the temperature sensors built into the cooling system. The E9X cooling system using an electric pump eliminates the risk of overheating the head. Why someone comes on here and says BMW's bleed procedure in the TIS is only for professional technicians working in dealership is just stupid.

Plus, it's such a simple and easy procedure follow.

[N52bigblock]

Originally Posted by Wolf 335

Just a comment...Every reputable independent bmw shop in my area claims that the system is self bleeding as well. And these are the guys that used to work for bmw before they left and opened their own shops.

I would guarantee that if you asked them to elaborate on what they mean by "self bleed" they would say they fill the cooling system then activate the pump and then it bleeds itself. Yeah it does bleed itself IF
you fill the system with the bleed screw undone, then tighten the bleed screw, put the cap on, and you ACTIVATE THE COOLANT PUMP. (just like it says in the bleed or venting procedure, strangley) You can quite happily walk away from it and it will bleed the air out of the cooling system, because the pump is circulating the coolant and venting the air into the expansion tank, then you simply top it up afterwards. I worked for BMW as well from 2003 until 2012 in 3 different countries and i have never seen or heard anybody not use the proper bleed procedure, except for an apprentice. He didn't do it once and overheated the car. It's a disaster waiting to happen. As Efthreeoh mentioned the procedure is so damn easy to do anyway. Why the hell wouldn't you? It would be far quicker (in reality less than 5 mins) to do it properly than to fart around waiting for all the bubbles to "hopefully" come out and keep topping it up for god knows how long. I'm done now. Promise!