thermostat
 

1983 300 d ,running real cool now i think fan clutch is a little tight , but if i squzze upper hose it bubbles in over flow tank when engine is stone cold. is thermostat bad?
i thought it should be closed at start up.

It should run above 80 degrees Centigrade once at operating temperature. If it never reaches that you need to replace the thermostat. These stats are designed to fail in the open position. I have had this happen a few times with MB stats.

Good luck,