Need help with an elusive coolant/water leak

[bikermice]

I have a 2000 E39 523i that loses coolant over a period of a couple of days when it stands. I have replaced the water pump, expansion tank and top hose, all to no effect. I cannot find any traces of coolant in the bottom covers at all and no other visible signs of leaks anywhere. Is anybody able to give a heads up to where the problem may possibly be ? It is really frustrating to have to keep topping up before using the car.

 

[Ahmedy]

Have you checked if it's mixing oil with water, also is there a lot of vapor in the exhaust. Have you blead it with the heater on max (optional preference for some)

 

[Benji]

Heater core? When you crank up the heat in the morning, do you smell coolant?

 

[Coisman]

Take the car to silverton radiators ore something and have it pressure tested.

 

[bikermice]

No coolant smell if the heater is on, system was bled with heater on full and there is no oil/ water mix at all. Have not had a pressure test done other than waiting for the car to get to operating temperature and checking all pipes etc. Guess I will take it in and have a check done.

 

[Mytfine]

Add a dye to the system and then use a blacklight.

 

[Coisman]

Trust me. Easiest way to spot a micro leak is with a pressure test. My radiator was leaking a mist spray behind the expansion tank. Only saw it with the pressure test

 

[getty150]

Investigate the expansion tank...what's happening is there's a crack in the expansion tank when the engine is warmed up and as the engine cools the tank crack seals up again

 

[bikermice]

Thank you, will do.