F40 M135i Coolant bleed

Maxvalentine · 2025-10-03T10:57:21-0400

Hello,

I recently bought a crashed M135i from Copart. I have had to replace the whole front end including rad packs and crash bars etc. I am attempting to repair it on my driveway and has been going well so far.

I tried to vacuum fill the coolant but it only sucked up 50% of it because there was some air bubbles in the tube. I am now at the stage where I need to bleed it. I have tried the bleed procedure online (fans on low, heat on high with ignition on and holding accelerator for 10-15 seconds but can’t hear the pump going.
I dont have a diagnostic tool yet but does anyone know of where the bleed screws are so I can bleed the coolant and run the engine?
I also dont know if the water pump works as when I got the car I ran it for 5 mins ish when there was no coolant in the car (I know very silly of me). Now I’m scared I’ve blown the water pump up.

anyone got any suggestions on how to proceed with bleeding it?

Johnnyroper · 2025-10-03T18:35:23-0400

The bleed screw is on the header tank by the cap, slacken screw and fill system up.

think it’s mechanical water pump on B48 rather than electric so that would explain the bleed procedure not working. Have a look at the aux belt and see what it’s driving to confirm.

Maxvalentine · 2025-10-05T13:54:27-0400

Hello,

Thank you for the quick reply. It looks like it’s got an electric coolant pump. Online it says that too. The screw you mentioned is a hose but it just goes directly into the tank, so would it matter if i loosened it when the coolant cap is already off?

Not sure what to do from here to get the bleed procedure to work. I can’t see any codes on the car for coolant problems.

payno · 2025-10-05T14:29:07-0400

Part numbers say its a mechanical water pump, https://www.realoem.com/bmw/enUS/showparts?id=7L12-EUR-06-2024-F40-BMW-M135iX&diagId=11_7793, as does a pic of a genuine BMW part, Pardon our interruption...

Johnnyroper · 2025-10-05T14:33:19-0400

https://www.realoem.com/bmw/enUS/showparts?id=7L12-EUR-02-2019-F40-BMW-M135iX&diagId=11_7793

Real oem shows mechanical pump.

just fill expansion tank up and run at idle keeping eye on the level, air will expell through the small pipes back to expansion tank

Maxvalentine · 2025-10-05T15:17:37-0400

Okay thank you. I think I was looking at the auxiliary pump here on eBay.

Pardon our interruption...

I just didn’t want to run the engine incase it breaks the pump. Will all the air come out when I run it or will I still have airlocks after?

I’ll keep an eye on temp tomorrow when I run it. Pretty sure you can get the secret menu open and see coolant temp temp from there. Scary moment as it’s the first time I’ve ran it since replacing the rad pack and the rest of the front end 🤣. Thank you both for your help so far

Johnnyroper · 2025-10-05T18:42:17-0400

I have always found them to bleed quite easily, either via the bleed on expansion tank (which yours does not have) or by it returning via the small degassing pipes.

just run to temp keeping eye on level then let it cool down and take cap off and top up as required

F40 M135i Coolant bleed

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