Originally Posted by TonyFromWestOz

Charles,
In my 300D, I took hot coolant from the heater hose connection to the head, near the oil filter housing, and returned the coolant to the heater hose adjacent to the water pump.

My car does not have the auxillary water pump, but I believe that the aux water pump is controlled by the ACC (Automatic Climate Control IIIRC - I don't have one ) and so may not allow coolant to flow to your fuel heater in some circumstances.
The source of coolant I use is not affected by anything other than the correct operation of the engine cooling system. It is effectively in parallel with the other connections to these points.
NOTE: when installing the Tee in the coolant hose near the oil filter, ensure that service access for the filter is not compromised.
I did post photos of the connections in the past, but do not recall when and I do not know how to search for particular photos.