A part you might be interested in learning a bit about is the Autmatic Climate Control Servo (ACC Servo). It's a part you'll probably replace every 3-4 years and if you don't pull it out of a junkyard car, it will cost you about $700-$1000. If memory is serving me (I've been working my my 88 560SEL too much and my 78 300CD has been well behaved lately so no need for anything other than oil changes) this part is what diverts coolant to the heater core when heat is demanded from the Climate Control System.

Good luck with your 300CD. I love mine and it's neat, although too rare to see another on the road!



Scott