[els_86]

It's so simple to do in our cars and it seems like every so often it would be a good idea to run the bleed process just to make sure no air bubbles are in there. Could this hurt the engine in any way, or am I missing something?

[jadnashuanh]

Except with a drain and a refill, it should be totally useless to randomly decide to bleed air from the system. Whatever air may be in there will dissolve and work its way out.

[els_86]

Originally Posted by jadnashuanh

Except with a drain and a refill, it should be totally useless to randomly decide to bleed air from the system. Whatever air may be in there will dissolve and work its way out.

Okay I was gonna add a little more coolant in the morning. I just did a coolant change so after I add a little more coolant in the morning I figured for good measure I would bleed it again. Even if this isn't going to do anything, it can't hurt to let's say "bleed the system too much" can it?

[jadnashuanh]

The level dropping is likely just the normal action of what little air was in there, working its way out, lowering the level. Just top it off and watch it. Unless you notice the vehicle temp getting higher than normal, water is circulating and everything's fine. Why throw away the expensive antifreeze? It's also toxic waste and you shouldn't just dump it on the ground or down the drain.

[els_86]

Originally Posted by jadnashuanh

The level dropping is likely just the normal action of what little air was in there, working its way out, lowering the level. Just top it off and watch it. Unless you notice the vehicle temp getting higher than normal, water is circulating and everything's fine. Why throw away the expensive antifreeze? It's also toxic waste and you shouldn't just dump it on the ground or down the drain.

I understand. But bleeding it too many times can't hurt anything right?

[els_86]

Also I have seem mixed opinions on this, but how much do you top off the coolant tank? I first thought to fill it to max, but then a mechanic said when it gets hot it will expand and if it's at max will have no where to go. So I filled it right to where thr red dipstick just sticks out of the top about an inch. I figure once it's hot, the dipstick would basically be at the full position.

[els_86]

Anyone?

[Efthreeoh]

els, you are seriously worrying about this way too much! I'll try to explain physics involved here so you get a better understanding.

When an engine has a full, or near-full cooling system, and the engine has been run (i.e. the system is pressurized), any air in the system is forced out of the system. The system is pressurized by the action of the water pump forcing the coolant around in the system and because as heat is generated the coolant is trying to change state from a liquid to a gas, so the pressure increases to keep the coolant as a liquid. A automotive cooling system's operating pressure is typically about 16 PSI. The coolant reservoir cap has a pressure relief valve built into it so that when the system reaches above 16 PSI the system will self-vent. Any gas (i.e. air) in the system will vent first.

For the E90, bleeding the system cold allows for any trapped air to be forced into the coolant reservoir, which then escapes to the atmosphere when you open the cap. Bleeding the system cold prevents any local overheating of the cylinder head due to air pockets that may be present after a drain and refill procedure. Air can get trapped in the cylinder head because it is generally the highest part of the engine and air always rises to the top of a void (you see this phenomenon every day when you look at your Gatorade). So operating the coolant pump on the E90 (with the engine cold) avoids the possibility of localized overheating of the cylinder head because the air is forced out without generating any heat from combustion. On cars with a belt driven pump, the easiest way to run the water pump is to start and run the engine, which in turn generates heat, which can locally overheat the cylinder head if air pockets are trapped in the cylinder head and coolant cant get there to remove the heat before the air is forced out (this is what I think you are unknowingly worried about); this doesn't happen in the E90 because the air is removed when the engine is cold.

Now, the reason you bleed the E90 system with the cap and bleed screw fully closed is allow the system to properly move any trapped air from the cylinder head to the coolant reservoir and establish the proper level of coolant; which you do when after the bleed when the pump stops, you open the reservoir - any trapped air escapes - and you top off the coolant. Leaving bleed screw open when you originally fill the coolant reservoir allows any trapped air in the reservoir to escape before you close up the system and bleed it. The proper coolant level is when the system is cold and the level indicator stick lower ball is even (level) with the reservoir neck (there is a pictogram embossed on the reservoir that shows this - it's hard to see and you may not have seen it). When the coolant is at this level (when cold) it allows for the proper expansion of the coolant.

Bottom line is if you would just follow the BMW procedure as several people have provided in the DIY section, you will have no issues with the coolant level and will not damage the engine. That said, you can run the bleeding procedure all you want (every day if you'd like) all it will do is unnecessarily drain the battery and run the water pump. Once the system is bled, it's bled. If there are no leaks in it then you need not worry about it other than to periodically check the coolant level.

Originally Posted by els_86

Also I have seem mixed opinions on this, but how much do you top off the coolant tank? I first thought to fill it to max, but then a mechanic said when it gets hot it will expand and if it's at max will have no where to go. So I filled it right to where thr red dipstick just sticks out of the top about an inch. I figure once it's hot, the dipstick would basically be at the full position.

Hmm...I'd make another thread about. You haven't beaten this dead horse enough already lol @ a repost of your own repost

[els_86]

Haha sorry guys im done talking about it now! I tested the coolant and it seems i added a little too much water. Can i just take a turkey baster and drain some out of the tank and theb add some of the concentrate to bring it to about a 50/50 level? Is it ok to suck some out with a tirkey baster and is it okay to add straight coolent like that? Last question i promise!!!!

[PINeely]

Originally Posted by els_86

Haha sorry guys im done talking about it now! I tested the coolant and it seems i added a little too much water. Can i just take a turkey baster and drain some out of the tank and theb add some of the concentrate to bring it to about a 50/50 level? Is it ok to suck some out with a tirkey baster and is it okay to add straight coolent like that? Last question i promise!!!!

You'll be fine. Water actually does a better job of cooling, you just can't use pure water because it A) boils B) freezes and C) corrodes your engine. Most people use a 50/50 mix but the exact ratio is not important.

If it really bothers you then there is nothing wrong with your turkey baster method. The concentrate will mix with the existing solution inside the radiator and engine.

[jadnashuanh]

Next time, if you need to ever add some to the cooling system, once it has the proper mixture, do not add pure water OR pure antifreeze...mix it up so you're adding it at your desired concentration (normally 50/50, but could be different if you're in a really extreme hot or cold climate).

To get it back to the 'proper' concentration is a nice review of algebra, or lots of trial and error.

[els_86]

Cool thanks so much guys. The only part I am still a bit confused on is how much to fill the expansion tank to when cold. For the bleeding procedure people are saying to full until coolant is coming out of the bleeder hole. However, it says on our cars to fill so the red dipstick is level with the cap. If I do this, nothing is coming out of the bleed hole. The only way to get fluid coming out of the bleed hole is to top it way off, and that is more than is recommended for a cold top off.

I filled it up to the point where the red dipstick was level with the top of the coolant tank and then bled.

[PINeely]

The Bentley manual says to fill it 100ml over the "max" line.

[els_86]

Hmm I thought if you fill it over the max line cold then when hot it would expand too much. I filled it so the red dipstick was level with the top and then bled it. Can anyone elaborate on the correct method or if they are both ok?

[PINeely]

Both will work fine but the Bentley manual procedure is the "correct" one recommended by BMW. 100ml over the max line on a cold fill is what it suggests. You'll have a really hard time overpressurizing the system.

Fwiw, I usually just fill to the max line because I don't carry around a graduated cylinder to add 100ml with lol.

[els_86]

Originally Posted by PINeely

Both will work fine but the Bentley manual procedure is the "correct" one recommended by BMW. 100ml over the max line on a cold fill is what it suggests. You'll have a really hard time overpressurizing the system.

Fwiw, I usually just fill to the max line because I don't carry around a graduated cylinder to add 100ml with lol.

Weird that the bently manual say that, because there is a diagram on our expansion tanks that shows us what the recommended cold max capacity should be, and that is the red dipstick level with the cap.

[els_86]

I would assume it doesn't matter if you fill it until coolant is coming out of the bleeder before bleeding the system. You are going to be introducing air when you take off the cap to the coolant expansion tank after you bleed so it's not like air is never introduced ...

[PINeely]

Exactly, and air stays in the ex-tank anyway. The idea is to keep the air pockets out of the cylinder head. Once the system is bled no more air is introduced to the head and the air that you see inside the expansion tank stays there. Think of it like a well; the water underground (inside the engine) has no air in it though it is free to circulate and the well (expansion tank) is just the above-ground access to it. The air in the well can't make it to the ground water. Really it is an exercise in bubbles rising to the top of a liquid system.

[Efthreeoh]

Are we still seriously talking about this?

The reservoir tank is at a level above the cylinder head. It is designed this way so that the air in system (air always collects in the highest void in container) collects in the reservoir, not in the cylinder head. As the block drains during the coolant procedure, the void is filled with air. As the new coolant is added to the system and fills the engine block the air is forced out of the cylinder head (the highest point in of the engine "block") through the small coolant tube that feeds into the top of the reservoir where the bleed screw is, which is why you keep the screw open when refilling the coolant. The small coolant tube connects to the upper radiator hose right at the upper radiator inlet, runs across the top of the radiator and over to the top of the coolant tank. The purpose of the tube is to provide for an easy path for air in the system to move back to the reservoir.