got a 2000 clk 320 and the cooling fan doesn't run, even when the engine overheated till the coolant boiled and steamed (that's actually how i realized the fan never worked since i bought the car couple months ago). the clk's onboard computer doesn't indicate any malfunction, all fuses are checked and good, nothing showed up even on a diagnostic computer in the auto shop. the shop owner told me i need to replace the thermostat but i don't think that's the source of the problem.

i've heard there's actually a fuse on a relay that controlls the fan on some mercedes models but haven't check this yet on my clk.

any other suggestions from any of you guys here??

First Check the UPPER and LOWER radiator hose..(IF) one is HOT and the Other is COLD then Yes the thermostat is defective..

If Both hoses are the same temp..Inspect the cooling fan switch

thanks mark... both hoses are hot and the fan works when directly supplied with 12v current. just seems there's no power going to the fan for some reason. maybe a faulty relay somewhere? i know faulty relays are common on some japanese cars, not sure if its the same with mercedes.

now, where's this fan switch you mentioned located?