Thanks to Mick J, tkamiya, ctaylor738, J.HIDALGO for your reply. I have read through your replies carefully and have tried to fix the problem.
Mick J: I don't understand what "viscous coupling" is, so I was unable to check for that.
tkamiya: I have also looked for the fuse in both driver side and under the bonnet. Fuse number 25 under the bonnet is for AUX Fan. This fues does not exist in my car as it is only for diesel models acording to the label on the fuse box cover.
ctaylor738: Do you mean the fan clutch as in the fan blade not rotating and being lose. If so I have also check for that and it seems to be fine.
J.HIDALGO: My car is an E230. I live in Scotland - Glasgow. I've not been able to find the coolant switch or thermostat. I have checked the coolant level, which seems to be fine. I also found some other information on the internet about mercedes coolant requirements. I'm not aware, what coolant the previous owner has used. Next thing I'm going to do is to buy new coolant from mercedes and flush out the old one.
I have got some digital pictures of the engine and radiator. but was unable to post them as picture attachment points to http://
path, which I don't know how to use on the forum.
I would like to thank all who have replied to my question.
I would appreciate any further help. Thanks..