A new system is at its loosest on the first drive. Joints that were tightened cold have just been through their first real heat cycle, the rubbers have taken a set, and every clearance you measured on stands has changed now that the car sits on its wheels under its own weight. Nothing has failed yet, and nothing has proved itself either.
Treat that trip as a baseline rather than a judgement. A short route with a steady cruise, some gentle acceleration and a few low-speed bumps tells you more than a long motorway run, because you need the system to move through different loads while you are still close to home and still listening to it.
Work backwards from the front. The joint closest to the engine sees the widest swing between cold and hot, so it is usually the first to lose preload or take up clearance. Look for a soot shadow at the mating faces, a polished edge where two flanges have rubbed, or a nut that no longer sits flat on its washer.
On a new stainless system a single settling is normal; a joint that moves twice is telling you something different. Usually the pipe was drawn into position by the fasteners instead of sitting square on its own, so the joint keeps relaxing as it heats and cools and never quite holds what you gave it.
Hangers are where an installation quietly fails. A rubber that has stretched into a new shape, a bracket that has swung off centre, or a hook that now rests against the edge of its mount all point to the system having found a different resting position once it was hot. Photograph them as they sit now, before you touch anything.
The check is simple: with the car level on the ground, the pipe should hang with each hanger roughly centred in its mount and no rubber pulled hard to one side. If one hanger is carrying the whole system, the others are doing nothing, and the loaded one will keep stretching until the pipe starts to move with it.
Look for witness marks before you look for damage. Bright polished spots on a subframe, a scuffed patch of underbody coating, or a clean line drawn through road grime on a pipe section all record contact that happened while you were driving. Contact comes first; damage comes later.
Check the fastener heads too. A bolt that has been working shows a shiny ring under its head and a disturbed layer of dirt around the washer, which is not the same as a bolt that was never tight. The difference matters, because one of those needs a new fastener and the other needs a joint that is lined up properly.
Two senses beat any tool at this stage. A tick that follows engine speed is exhaust, a tick that follows the road surface is contact, and a tick that appears only when everything is cold is usually a gasket face that has not yet expanded into its seat. Listen with the windows down at low speed, where the sources separate.
Smell is the other early signal. A new system normally has something on it to burn off, and that smell fades as the surfaces clean themselves. A smell that grows stronger rather than weaker, or one that arrives with a visible haze at the tailpipe, is not burn-off and should be found before the next drive rather than monitored.
Give the system a proper second look once it has cooled completely after that drive. Everything that is going to move has moved by then, and everything is back at a size you can measure. This is the moment to correct a joint, reseat a hanger, or accept that the installation has simply settled where it wants to sit.
If nothing has moved, stop checking. Re-tightening a joint that is already stable only removes the margin the fastener was holding, and the third visit to the same nut is usually the one that damages it. Two checks, then trust the work until something actually sounds wrong or leaves a stain.
