Coolant light query

[JimmyMc]

Hello
I have a 1990 320i M20.
Have recently flushed the system as the coolant sensor needed changing.
Bled the system best I could. Now, when I bring the car to a stop, after driving for 15-20 mins, with the engine still running, the coolant light comes on.
Next day, if untouched, the light will be off.
I think air is trapped, and when heated, compresses and lowers the level. Plenty in the tank before, and after.
If it’s air, how do I get it out. Nothing else is coming out of the nipple.

[Bonymaenjack]

Hello
I have a 1990 320i M20.
Have recently flushed the system as the coolant sensor needed changing.
Bled the system best I could. Now, when I bring the car to a stop, after driving for 15-20 mins, with the engine still running, the coolant light comes on.
Next day, if untouched, the light will be off.
I think air is trapped, and when heated, compresses and lowers the level. Plenty in the tank before, and after.
If it’s air, how do I get it out. Nothing else is coming out of the nipple.

Take a look at this
https://www.e30zone.net/e30wiki/index.p ... g#Bleeding

[JimmyMc]

I’ve tried bleeding the system with the nose raised. Filled the rad before connecting the top hose.
Air blows hot and was turned on throughout. Temp sits at mid point or just below. Doesn’t overheat. Rad is new.

[fixedwheelnut]

I’ve tried bleeding the system with the nose raised. Filled the rad before connecting the top hose.
Air blows hot and was turned on throughout. Temp sits at mid point or just below. Doesn’t overheat. Rad is new.

Rather than using the small bleed screw undo one of the temp switch blanking plugs as in the photo above, fill up cold until water runs out there, then fill up header tank, refit blanking plug, run engine with heater on hot at approx 300rpm until the coolant can be see circulating in the header tank, top up more if required, fit the cap and run it until hot, then re check the level when cold again, next day usually.

[JimmyMc]

Thanks. So should I drain and start again?

[mark_i]

Hey Jimmy. draining not necessary.
2 things i would check:
i/ the thin tube from the top of radiator to expansion tank is clear
ii/ maybe a level sensor wiring issue . ..

[JimmyMc]

Hey Jimmy. draining not necessary.
2 things i would check:
i/ the thin tube from the top of radiator to expansion tank is clear
ii/ maybe a level sensor wiring issue . ..

Thanks. I’ll investigate those. I think the top small rad hose is okay though.