I want to try to bleed the coolant in my 2008 Clubman R55, as I think there may be an air bubble. I am paranoid about the bleed screw, because I've read it can come out.

Not sure if I should expect any coolant to come out cold and not started?

I turned a few turns and chickened out. Nothing comes out. (And where will I see it?)

Can somebody suggest exactly how many turns are safe, and screw will not come out? I sure as hell don't want to get squirted with hot coolant!

 

Maybe Henry James knows…

 

Coolant will come out before the screw comes all the way out. Even if it does you can just screw it back in since you'll release all the pressure when opening the screw. Its like 4 or 5 full turns before it wants to come out. Just turn it until you see coolant come out or hear air come out. Should really only take like 2 or 2 and a half turns for coolant to come out.

 

In order to bleed properly, first take a spin with the AC set to full heat/minimum ventilation until the engine reaches its operational temperature. Keep the engine (and heater) running while bleeding the system. This will ensure that the thermostat is open and coolant running through the pipes. Beware of the hot engine and coolant.

The (riskier) alternative would be to bleed cold and keep coolant level in sight until it no longer drops when using the car (replenishing coolant whenever its level in the expansion tank drops). The risk in this variant is that if a "bubble" gets stuck around the temperature sensor, the latter may report lower temperatures than those inside the engine.

 

I tested this on my new thermostat before installing. I got around 7 full turns before the screw came out and you need about 3 full turns to get coolant flowing for bleeding.

cheers
MacMini34