Got a Sierra estate with an Endura-D engine. Coolant system is an unholy mess, coolant is somewhere between mud and Guinness in colour. I'm currently in the process of replacing the head gasket and then I'm gonna take advantage of the fact that the coolant's already drained to flush as much of the muck out as humanly possible. Can't find much info on how to do that though - Haynes manual for the Sierra doesn't cover the diesel, and although I've found the manual for the Fiesta with the later version of the same engine online, I'm not sure how similar the two coolant systems are?

Any advice?

Cheers!