1995 E320 overheating and knocking at signal lights

Can someone help with ideas about what to check or could be wrong. The temperature slowwly rises when the car is stopped and the Engine is running. It goes close to 120 in the temperature guage. Running car
operates around 80 degrees. Please help. One mechanic told me fan clutch is bad. Any other ideas?
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Listen to the fellow who diagnosed a bad fan clutch. I believe the electric fan should also run when the engine's temperature reaches 100 degrees C.
The good news is that the radiator is OK because the engine runs at 80 degrees C on the road, as it should.
The knocking you hear is preignition because the engine is too hot for the fuel grade - are you buying premium? Probably not.
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Assuming your aux fans are not coming on, Here is a test . There are two auxilary electric fans in front of the radiator. With car off, see if these turn freely by hand.- If OK >>>>>> Next: There is a 2 wire sensor on top of the thermostat housing . It has a blue base. It turns the fans on to high speed at 105/107C. With the car running, unplug this connector and see if the high speed fans come on. [ if yes , you have a bad sensor] If NO , the most common fault is the fan feed fuse. This fuse is not in the fuse box. It is in the relay box behind the fuse box. This will require the removal of 6 phillips holding screws for removal of the lid. You will now see the relays . The one in Slot "C" is is the high fan relay and the fuse will be on top of this relay. Pull the fuse and check it. While you are there , the next relay back [ slot "B" ] should also be checked . This is the fuse/relay for the low speed fan. This fuse was originaly 15 amp, but has been modifies by Benz 25, so do that while you are in there. If you found a bad fuse , relplace and repeat the first test at the sensor for fan operation. If OK, take it for a ride ..and let us know .. Don't use a/c on first test . as a/c is low fan operation on 124s.
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