Hoses fail from heat when the heat is concentrated. In a roomy bay, air moves around a hose and carries heat away from it. In a tight one the hose sits near a manifold, a downpipe or a turbo housing, and the only path left for heat is into the rubber.
So the same hose can last years in one car and fail within months in another. The hose has not changed. The distance to the nearest hot surface has, and that distance is usually the only variable you can control.
Radiant heat crosses a gap without touching anything. Conducted heat arrives through contact, and it does more damage because there is no air to carry it away. A hose resting on a hot pipe is being cooked along a line rather than warmed evenly.
That is why a hose with a visible flat or a shiny, hardened band on one side has usually been touching something. The band marks the contact line, and the hardness says the material has already lost the plasticiser that made it flexible.
Heat also reaches a hose through its fittings. A metal clamp conducts from the pipe into the hose wall, and a metal joiner does the same along its whole length. The hose then fails beside the fitting rather than in the middle of the run.
Look at the ends first when a hose has failed. A split that starts at the clamp and runs along the wall is a problem of heat and movement at the joint, not a material problem in the middle of the hose.
A barrier works by interrupting the path, so where it sits matters more than what it is made of. A shield placed between the hose and the source with an air gap on both sides is effective. The same shield wrapped tightly around the hose is much less so.
Reflective sleeving helps against radiation and does very little against contact. A formed exhaust heat blanket on the hot part lowers the surface that faces the hose, which is often easier than shielding the hose itself.
A hose gives warning. It hardens, it takes a set in the shape it was bent into, it develops fine cracks at the clamp, and it begins to weep at a fitting. Any of those is the start of the end rather than a cosmetic issue to be watched.
A squeeze test is still useful, but only against a new hose of the same type, because the feel is relative. If the wall does not spring back, or the surface cracks when it is bent, the silicone hose has already changed and no amount of shielding will reverse it.
Shielding is the cheaper answer and the right one when the hose passes a heat source on an otherwise fixed route. Rerouting is the right answer when the hose runs parallel to a hot part for most of its length, because shielding a long run costs as much as changing it.
The decision rule: if the hot section is shorter than your hand, shield it. If it is longer than the hose itself, reroute. A hose that can run clear in a tight bay usually needs a bend or a different fitting angle rather than a different material.
