Losing coolant...

[Truvalu]

I had the thermostat replaced about 2 months ago as the temp guage always used to stay very cold on the open road.

Now I keep on filling up with coolant and I can't find anywhere that it might go.
No water in the oil (dipstick).
No obvious visible leaks.
Temp stays normal, so no overheating.
Expansion tank never totally empty.

 

[Nic_s]

I had the thermostat replaced about 2 months ago as the temp guage always used to stay very cold on the open road.

Now I keep on filling up with coolant and I can't find anywhere that it might go.
No water in the oil (dipstick).
No obvious visible leaks.
Temp stays normal, so no overheating.
Expansion tank never totally empty.

I had the same issue until I saw green marks against the radiator. Have a nice close look at the radiator for any water marks or after a good drive for any leaks. Not to clued up on where the E39's tend to leak though.

 

[moranor@axis]

get a pressure test done...

 

[Truvalu]

I just had the engine run for a good 10 minutes while I bled the coolant system.
Will keep an eye on it and see if it stays level.

 

[StK]

Try bleeding it properly and put on a new radiator cap. E39's are notoriously hard to bleed so you may have to lift the front end up as high as you possibly can. After you have done this and you are still losing coolant then there will be a leak somewhere......hopefully not HG, you can get a sniff test done to check the HG but try first things first. Good luck

 

[Truvalu]

Thanks for the advice guys,

I have done the 2L water bottle bleeding process...........
You put the filled 2L bottle upside down in the filler tank after removing the caps. All happens with the engine running.
First you loosen the bleeding screw nearest to the thermostat and let as much as possible of the air out and close it.
Next is the bleeding screw next to the filler cap and close that after no more visible bubbles.
Remove the bottle and replace the filler cap.