I've had no problems with Dex in any of the vehicles I've used it in:
2011 Crown Vic LX 4.6 V8 (iron block, alum heads)
2005 Crown Vic PI 4.6 V8 (iron block, alum heads)
2009 Chevy Malibu 2.4 I4 (alum block, alum heads)
1998 Ford F150 5.4 V8 (iron block, alum heads)
1999 Cadillac Eldorado 4.6 V8 (alum block, alum heads)
1995 Cadillac Deville 4.9 V8 (alum block, iron heads)
1991 Cadillac Deville 4.9 V8 (alum block, iron heads)
1990 Cadillac Eldorado 4.5 V8 (alum block, iron heads))
1989 Cadillac Eldorado 4.5 V8 (alum block, iron heads)
1988 Olds Cutlass Supreme 2.8 V6 (iron block, alum heads)
That's a lot of vehicles and a lot of miles. Lots of cast iron parts. Most of the vehicles on that list didn't even come with Dex as factory fill, and I still have yet to experience problems with Dex.
Here are some pics from a t-stat change in the 2011 Crown Vic. See any hint of problems?