Block heater. Where is it?

I just bought the 96' E300D. It is my first MB. It has 87KMiles. It looks like my glow plugs are bad because the preglow light does not start after I turn the ignition but it lights up after I start the engin. I'd like to find out if I can use the block heater to warm it up. The engine starts with no problem but it makes knocking noise, shakes badly and produces lot's of smoke. After the engin reaches the right temperature the smoke stops and engine runs smooth.

Any idea where would be a good place to buy the plugs from?

Also I get the message that the water coolant is low (display malfunction) even though it is at the right level. Is that the sensor? Can this also cause the chceck engin to be on?

Please give me some hints. Thanks.

heater block, i think you have to empty up the coolant below the engine with an X allen keys (4 scew,and replace on them with the heater block. A hassle mechanical job

I thought that there is a block heater already installed. Shouldn't there be some electrical plug where I would plug my extension cord? I wonder.