For cables near heat sources like headers I use a high temp fiberglass sleeve. You can buy it from McMaster-Carr by the foot. For things like starter cables, speedometer cables etc,the 3/4 inch stuff works well. Part number 2592K64
For radiant heat issues, like a starter motor, or evaporator box underhood I like to use the aluminum faced fiberglass insulation. Part number 88475K2 It should be installed foil side to heat source. I know it looks like a spaceship, but it works. Wrapping a starter motor will really reduce the temperature. We went to the moon & back using that stuff. Works well in lots of places, and unlike some other products (dynamat) it is not flammable.
B.