I did my truck today a 2006 F-450 with 52,000 miles, Ford says you can go 100,000 on the factory coolant. Well I decided I'am not going to do that and I did a flush with distilled water I didn't use the flushing VC9 fluid your asking for troubles using a cleaner. I drained the rad and refilled with plain water drove around flushed it out did it again flushed it out, used a hose and flushed out the expansion tank while running the engine. Filled the rad up with distilled water flushed out the tap water then refilled the rad with new FORD Premium gold coolant. Lets just say the coolant that came out of the rad looks like a dark ale beer it is really dark looking I was really surprised when I seen the color of the new coolant. So there is lots of crap or rust in the old coolant if I left it till 100,000 miles I may end up with oil cooler problems. So my advice to anybody with a 6.0 PSD and you never had a rad flush and coolant change do it right away. For us Canadians Ford Premium Gold is 28 dollars a gallon from the Ford dealer and you need to use the Ford coolant. Took me about 5 hours to flush out the old coolant and replace it with new.