Does anyone know how I go about bleeding a radiator for a 1987 300D? Problem with refilling cooling system. air lock? Help!

Welcome to the forum.

These engines can get difficult at times with air.

Take the upper radiator hose off the radiator, carefully (don't break the plastic nipple ) and pour as much coolant as you possibly can into the head. When it won't take any more, then reconnect the hose.

Put the cap on and take it for a drive with the heater on high ( ). This will circulate coolant through the heater core and drive any air out of the heater core.

Watch the temperature gauge. It should not go over 100°C.

Let it cool off completely and refill it to the cold mark the next morning.

You may need to repeat the filling for a couple of days as the air slowly works it's way out of the system.

Some have had additional success by lifting the front end during the fill process. Get's the radiator higher in the system and let's the air rise to the top.

I drill a 1/16" or next size larger hole in the thermostat, (where the up arrow is), I drill all my new thermostats, even on my pickup, if they do not have a jiggle pin in the new thermostat..
This small hole will bleed the air out and save a lot of air lock problems.
I have posted this before, but I guess no one believes me.

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1985 300D California w/cat. (257,000 + Miles)
1980 300SD (208,000 + Miles)

Thanks for the welcome! I will try it and let you know.