Re: 05 F-250 Diesel
It'd be good to contact your dealer to get more information on this death shake.
I run Prestone 50/50 in all my vehicles (2006 Sprinter diesel as well as those listed in my sig) with no problems in over a decade of using it. I change it every 100K although I can go farther.
If you take the rad cap off, and you see white gunk at the top starting to accumulate around the edge you know it's time for a coolant flush.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!