[applehusky]

After the radiator vent hose on my '14 335i gt broke and let some coolant out, I had to follow a procedure for bleeding the system after filling the coolant back up.

I was wondering if anyone knew why they don't tell you to just turn the engine on and drive around in order to get the air out.

I have thoughts but I'm wondering if anyone here "in the know" could shed some light on this.

[Billfitz]

If you don't bleed the air out you can't fully fill the system with coolant. There will be pockets of air trapped in the hoses. If you run the engine it and the transmission could overheat and cause damage to a number of components, starting with the water pump and getting progressively worse from there.

[applehusky]

Interesting
I knew why the bleeding needed to happen, just thought it was odd that it had to be done separately from starting the engine.

So it's basically just to minimize the risk of the engine overheating while filling the coolant?

[Billfitz]

No, it's to get rid of air in the system. The system is sealed, so any air trapped in it will stay in it unless purged. That's the reason why the coolant must be put into the circuit under pressure as well. It's not your father's Oldsmobile.

[applehusky]

Originally Posted by Billfitz

No, it's to get rid of air in the system. The system is sealed, so any air trapped in it will stay in it unless purged. That's the reason why the coolant must be put into the circuit under pressure as well. It's not your father's Oldsmobile.

oh I knew what bleeding was and why it needs to happen. sorry for not being clear.

my question had to do with the way BMW chose to have it done. I'm having a conversation with a friend of mine about how you bleed the system on a BMW as opposed to another type of car. in his opinion, BMW's procedure is unnecessary complicated. however, I think there's a good reason behind it because procedures like these don't exist just because.

so, this is my question: what is the design problem that BMW were trying to solve by creating a procedure that bleeds the coolant circuit without the engine running?

[Billfitz]

I don't see a design problem per se. Coolant doesn't fully circulate through the system until the engine comes up to operating temperature, so if you wait for that to happen before the system can purge trapped air damage can occur before the air gets out of the system. If you purge the air without running the engine that can't happen.

[applehusky]

Originally Posted by Billfitz

I don't see a design problem per se. Coolant doesn't fully circulate through the system until the engine comes up to operating temperature, so if you wait for that to happen before the system can purge trapped air damage can occur before the air gets out of the system. If you purge the air without running the engine that can't happen.

that makes sense

[328iX]

What he's referring too is a thermostat, the coolant isn't circulating until it's up to temperature, thermostat opens and then it goes through the whole system.

Don't forget to turn your heater on fully so the water can pass through the heater core as well.


Also, no car can be bled by driving it around, even an oldsmobile or a honda, they either have a bleeder screw at the highest point of the cooling system, or it's done through the overflow/radiator cap.

[Wellingtonz]

Originally Posted by Billfitz

No, it's to get rid of air in the system. The system is sealed, so any air trapped in it will stay in it unless purged. That's the reason why the coolant must be put into the circuit under pressure as well. It's not your father's Oldsmobile.

can air trapped in the system cause coolant to disappear?

I previously had the overheat warning came up without any low coolant warning at all and found out the tank was empty.

I didn't know about bleeding or anything as I was at the highway and panicked so I just poured in distilled water and then bought bmw coolant and topped up the tank until around max marking but it keeps disappearing.

I've tried changing the coolant cap but it's still disappearing.

people are saying maybe it leaked into the transmission but the car shifts fine

[Billfitz]

The only place that coolant could disappear without a trace is through the engine and out the exhaust via a head gasket leak. Otherwise you'd see it on the ground under the car.

[Wellingtonz]

Originally Posted by Billfitz

The only place that coolant could disappear without a trace is through the engine and out the exhaust via a head gasket leak. Otherwise you'd see it on the ground under the car.

wouldn't a leaking head cause the coolant to mix with the engine oil? I've been keeping an eye on the cap for any milky residue but nothing.

I've heard multiple people say transmission heat exchanger but not sure how to determine it

[Billfitz]

It might, or it might just allow it to get sucked into one or more cylinders. That I know from experience. I don't see the tranny heat exchanger being the cause, it would fill the transmission with coolant.

[AspektUSA]

BMW very specifically says you can only change the coolant using a vacuum tool.

Using a can or bucket isn't kosher per TIS.

[Wellingtonz]

Originally Posted by Billfitz

It might, or it might just allow it to get sucked into one or more cylinders. That I know from experience. I don't see the tranny heat exchanger being the cause, it would fill the transmission with coolant.

How do I confirm it?

[Billfitz]

Catch the exhaust drippings. Coolant will be obvious by the color.

[Wellingtonz]

Originally Posted by Billfitz

Catch the exhaust drippings. Coolant will be obvious by the color.

I observed the exhaust during warm up just now and nothing. no smoke or liquid

[Wellingtonz]

Originally Posted by Billfitz

Catch the exhaust drippings. Coolant will be obvious by the color.

could air in the cooling system cause this? I forgot to clarify that the coolant level drops from max to around minimum or slightly below not fully empty. each Time i only top up around 300-400ml before it reaches max be it a few days later or it can be weeks after the initial top up

[Billfitz]

I can't say from personal experience.

[F32Fleet]

Originally Posted by AspektUSA

BMW very specifically says you can only change the coolant using a vacuum tool.

Using a can or bucket isn't kosher per TIS.

TIS is written for a shop environment not DIY'er

[SuperLomi]

Originally Posted by F32Fleet

TIS is written for a shop environment not DIY'er

While true, to get the fill correct in one go this is the only way.

For the DIY method: Even after doing the bleed process multiple times, you’ll still probably see coolant level drop and need to be topped up after driving for a bit.

[AspektUSA]

Originally Posted by SuperLomi

While true, to get the fill correct in one go this is the only way.

For the DIY method: Even after doing the bleed process multiple times, you’ll still probably see coolant level drop and need to be topped up after driving for a bit.

Yes, given that there is around 14.5 liters of coolant between the hot and low temp circuits in the B58 series - I'd just go ahead and get the $60 tool from ECS to do so.

Why risk it?

[SuperLomi]

Originally Posted by AspektUSA

Yes, given that there is around 14.5 liters of coolant between the hot and low temp circuits in the B58 series - I'd just go ahead and get the $60 tool from ECS to do so.

Why risk it?

I mean you still need other things, like a compressor which aren’t cheap.

The DIY method works, it’s just more work, time, and care. Which is why the official method isn’t that.