[fortythirtyfive]

Last June I did a coolant flush as I noticed my levels were pretty low.

From what I recall I filled it up just below the halfway line after 2 successful automated bleeds.

Tonight I noticed it was looking low again.. should it really be burning off that much in nearly 12 months?



I have enough fluid left so I can always schedule some time in to do another flush and top up.

[Billfitz]

It shouldn't burn off any. So long as you don't have an overheating problem, or a leak, adding more will eventually purge air from the system.

[fortythirtyfive]

Originally Posted by Billfitz

It shouldn't burn off any. So long as you don't have an overheating problem, or a leak, adding more will eventually purge air from the system.

Topped it up and ran the bleeding procedure. It dropped just as low again so I'm going to guess (and pray) it was a few bits of trapped air. Anyway, ran the procedure 4 more times to be super super sure and eventually it held right on the seam.

Also, am I being an idiot here? I was always told to crack the vent screw a tiny amount whilst it's bleeding, however that's right above the vent pipe and when it's bleeding it pours fluid EVERYWHERE. I don't remember it doing this last time? In the end I just ran the procedures with the cap off.

Screwed it back on and went for a 25 minute drive, got back and undid the cap and loads more air came out.

I'll keep an eye on it.

[AlmondJayRoM3]

Originally Posted by fortythirtyfive

Topped it up and ran the bleeding procedure. It dropped just as low again so I'm going to guess (and pray) it was a few bits of trapped air. Anyway, ran the procedure 4 more times to be super super sure and eventually it held right on the seam.

Also, am I being an idiot here? I was always told to crack the vent screw a tiny amount whilst it's bleeding, however that's right above the vent pipe and when it's bleeding it pours fluid EVERYWHERE. I don't remember it doing this last time? In the end I just ran the procedures with the cap off.

Screwed it back on and went for a 25 minute drive, got back and undid the cap and loads more air came out.

I'll keep an eye on it.

Venting while doing the bleed procedure is not called out in the tech manual. I’m guessing you didn’t do a vacuum fill which IS called for in the tech manual in addition to a bleed procedure. The cooling system on these cars is complicated and leaves a lot of places that can trap air. Doing the vacuum fill eliminates a lot of potential spots for that air to get trapped into.

Also the air coming out of the cap is only because the system is pressurized from the heat (PV=NRT and that jazz), not necessarily trapped air in the coolant system. It is always going to do that regardless of anything that happens in the system. Only way you know is that coolant level lowers. In other words don’t keep venting the system and keep an eye out for level. Only open the system when you have to refill.

[fortythirtyfive]

Originally Posted by AlmondJayRoM3

Venting while doing the bleed procedure is not called out in the tech manual. I’m guessing you didn’t do a vacuum fill which IS called for in the tech manual in addition to a bleed procedure. The cooling system on these cars is complicated and leaves a lot of places that can trap air. Doing the vacuum fill eliminates a lot of potential spots for that air to get trapped into.

Also the air coming out of the cap is only because the system is pressurized from the heat (PV=NRT and that jazz), not necessarily trapped air in the coolant system. It is always going to do that regardless of anything that happens in the system. Only way you know is that coolant level lowers. In other words don’t keep venting the system and keep an eye out for level. Only open the system when you have to refill.

Yeah fair enough, I presumed it would be negative pressure though rather positive though.

Vacuum filling pretty much eliminates the bleed procedure - I appreciate it's mentioned to use both in the old TSB but it has since been proven that topping up the coolant manually and using the automated bleed procedure works just as well.

[AlmondJayRoM3]

Originally Posted by fortythirtyfive

Yeah fair enough, I presumed it would be negative pressure though rather positive though.

Vacuum filling pretty much eliminates the bleed procedure - I appreciate it's mentioned to use both in the old TSB but it has since been proven that topping up the coolant manually and using the automated bleed procedure works just as well.

As you already figured out, standard bleeding works… eventually…but it is not efficient in terms of time and effort. Used it all the time with simple single circuit cooling systems.

But there’s a reason BMW instructions says damage might occur if you don’t do the vacuum fill. Air pockets can be left in the engine and leave localized hotspots throughout. Those hotspots aren’t measured by any of the sensors either. But you do you.