Sprinter loosing coolant through overflow-no sign of leak

[Ljh1]

Sprinter (55 plate) is loosing coolant through the overflow (via bottle test), replaced the radiator cap but it's still coming out of the overflow pipe. Temp staying at around 80 or just under so it's not overheating. Any ideas/suggestions greatly welcomed.

Thanks

 

[sallison1504]

Have you changed the lid to the expansion bottle?

 

[Ljh1]

It hasn't got an expansion bottle,the overflow pipe comes put of the rad neck.