After purchasing my 1985 300D I found that the former owner had bypassed the heater core. After talking to him, I am still not sure if the heater core was leaking or it was another problem. He was a Greek gentleman and could not speak English very well. He lived in Miami and all he could tell me is that you don't need a heater in Miami and it was too expensive to fix. I live in Central FL and it gets cold enough here that you need a heater.

My question is:

How prone are the heater cores to leaking??? or could it be the mono valve.

Second question - Since he removed the heater lines from the mono valve, and just ran a heater hose around the back of the engine straight into the block, which direction does the water flow in? The two small fittings and out the large fitting?

Would like to try flushing it with water and checking to see if there are any leaks before I try to take the heat core out of the car.

Thanks a lot for any suggestions

Dave