E39 coolant loss

[Brianmoooore]

528i began to show slight overheating on the way home last night. Coolant bottle was empty this morning, so I filled it up, and drove the car onto the ramp in the workshop.
No signs of water dripping while the engine was running then, but there was plenty of sticky coolant around the engine bay, which seemed to at it densest near the front of the engine on the LH side.
Though I'd fill and rough bleed the system before connecting up the pressure testing kit, so filled the bottle to the brim, and went to unscrew the black plastic bleed screw in the top radiator hose near the water pump.
As soon as I touched the screw, the head fell right off.
Heated the end of a flat blade screwdriver, pushed it into the top of the remains of the screw, cooled the screwdriver, pushed it back into the slot I'd made, unscrewed it, raided an old M40 radiator for a replacement, filled the bottle, fitted the replacement screw, bled the radiator.
Job done.
Wish all potentially expensive repairs were that simple!

[Jesus325iTouring]

Much like my P38 off roader Brian. It's the 4.6V8, had a serious overheat problem one day. This led to much speculation of blown head gaskets, porous blocks, slipped liners etc. Upon checking the basics, thermostat, rad flush etc I discovered the actual cause was a blocked pipe from the rad to the header tank. Very small thin pipe blocked with a blob of gasket sealant where the previous fitted a new water pump. Blockage cleared, cooling system rebled, now all fine.

[Speedtouch]

Nice method of extracting a broken bleed screw, but did you get to the bottom of what caused the water loss in the first place?

I know the E39 radiator header tanks are prone to developing leaks - I check the level on mine every week, just in case...

[Brianmoooore]

but did you get to the bottom of what caused the water loss in the first place?

It was the bleed screw - the head was just lying there, not attached to the rest of the screw, and the coolant was escaping up the small slot in the thread. Another case of the notorious BMW black coolant system plastics.

[DanThe]

Im on the second expansion tank on my 540 and thats showing signs of leaking now, Febi item, so was expected to be quality

The E39 electric controlled thermostats are complete and utter junk, its the main reason why everything gets so hot, the pressure gets so high and things fail. Although ive fitted an 80 degree normal thermostat I still see in the hot summer weather up to 99 degrees on the dash. I have since fitted a Spal pusher fan after the second original aux fan died, next on the job list is to try a lower temp fan control switch in the rad.

[Simon13]

you just don't get these issues on the e34 e36 stuff as the cooling systems aren't runing under such pressure. E46 systems can be like the e39s

[DanThe]

E36 328i suffered from overheating with their 93 degree stat, plastic parts and guage that tells lies, definitely more to do with neglect if they did overheat though.
Standard 540i thermostat is 110 degrees, the guage doesnt just tell lies, its a complete waste of space in the dash... just stupidity...

[Simon13]

E36's are fine