Radiator Flush Time
 

Well my father is taking a trip in the 87 300d turbo next weekend and wants me to flush the radiator and add new coolant before the trip. The car runs hot usually. My questions for you are:

1: Where is the plug (I don't have a manual), a picture would be helpful

2: Approx how much coolant will need to be added to re-fill the radiator?

3: Should regular anti-freeze or 50/50 be purchased?

Thats all the questions I have for now, thanks much in advance.

search citric above, you will find tons of info there.
on the 603, ESPECIALLY if it is running hot, you really need to keep it clean and fresh or you will be replacing the motor.
the drain plug should be just above the oil pan in the center of the block look for a random bolt protruding from the block. should be 19mm, but I do not have a 603,
do a detergent flush, several water flushes, and a citric acid flush and several more water flushes. all draining out the drain plug on the block and flushing very very very well.
then fill with a mix of 50% distilled water and 50% Mercedes coolant, or zeres G-05 it should take around 3 gallons of mix.

While you're at it, slide the windshield-washer bottle up and out, and remove the auxiliary pump below it. This will drain the heater core and allow you to see if the pump runs free, if it doesn't turn easily with a small screwdriver or other small probe, replace it while your CCU is still good.