Insulation and connector housings are often the first things to suffer, because those materials are chosen for electrical properties and cost rather than for heat. Look for hardening, a sheen where plasticiser has been drawn out, cracked loom tape, or terminals that have gone loose inside a housing that has crept. Once a connector has been cycled to that point it will not recover.
The fix is not to move the loom if the harness shape fixes the routing. It is to put something between the loom and the heat source. A shaped exhaust heat shield fixed to the body or the engine, rather than to the hot part, keeps the air gap intact and does the job without disturbing the harness.
Clips, cable ties, sensor bodies, fan shrouds and undertrays soften and then crack. A tie that has turned brittle is a reliable early warning, because it fails at a temperature where nothing else looks wrong yet. Battery boxes, reservoirs and covers deform slowly and often show a wave or a shine on the face nearest the heat.
Replacements are cheap but the failure is not, because a cracked clip lets a loom drop onto a manifold or a belt. Protecting the area ahead of the failure is more reliable than replacing the same parts in the same bad location over and over.
Rubber loses its elasticity with heat. Engine and gearbox mounts, exhaust hangers, bushings and flexible boots all harden from the hot side inward. A mount that has stiffened transmits more vibration, which accelerates wear elsewhere. A cracked boot near a turbo or a manifold will fail long before its counterpart on the cool side of the engine.
This is where a targeted wrap helps, because the hot part itself is the source and the rubber may be wrapped around it. Covering the tube that passes closest to the rubber with an exhaust heat blanket lowers the temperature the rubber sees, and keeps a flexible part flexible for longer.
Fuel lines, brake lines, power steering pipes and oil feeds do not like local hot spots. Fluid inside a line that runs close to an exhaust can heat-soak while the car is parked, and repeated cycles stress seals and fittings. A line that is uncomfortable to touch after a short run needs attention before a clip or a fitting lets go.
The answer is separation first, then shielding. Re-route if the line allows it, and where it cannot be moved, place protection between the line and the source so the line keeps a stable stand-off. Check the whole run, not just the obvious point of contact.
Under-bonnet paint, seam sealer, underseal and sound deadening all bake. The symptoms are dulled or chalky paint near the top of the bay, sealer that has shrunk back from a seam, and deadening that has sagged onto the floor. On a road car this stays cosmetic until water gets into a seam and the rust begins.
Guards over the hot section are common here, especially along bulkheads and floors. Match the protection to the panel area rather than to the pipe shape, because the goal is simply to keep the surface below the point where coatings start to move.
Walk the bay after a run and note every surface that is uncomfortably hot, every hardened tie and every discoloured clip. That list tells you where heat is actually going, which is far more useful than covering the whole engine bay. Then place protection along the line of sight between source and victim.
A shield handles flat areas, panels and bulkheads. For the tube itself, an exhaust heat blanket is the better tool where the pipe passes close to several things at once. Attack the specific points you found, then check them again after a few thousand kilometres of real use.
