By this point the system has written its history on itself. Stainless takes on a straw to brown tint near the hottest sections, and titanium moves through a range of colours in bands that follow the welds and the heat-affected zones. Both are oxide films forming on the surface, and both are normal.
The information worth reading is the pattern rather than the colour. A tint that runs evenly along a pipe says the heat is even. A single bright or dark patch says something local is happening: a shield resting on the pipe, a restriction, or a leak drawing air across hot metal. Read the pattern first and the colour second.
Soot collects where flow is slow and where gas escapes. In a healthy system it is light, even, and concentrated near the tailpipe. In a system with a leak it appears as a fan at a joint. In a system running rich it is heavy everywhere and the tailpipe is black inside, which is a mixture question rather than an exhaust one.
Look inside the tip and at the inside of the first bend after each joint. A clean joint with soot downstream of it means gas is passing through as it should. A stain radiating outwards from a joint face means gas has found a second exit, and it has been finding it long enough to leave a mark on the metal.
Staining is discolouration that sits on the surface and leaves the metal underneath unchanged. Pitting is a small crater you can feel with a fingernail, often with a dark centre. Staining is cosmetic and can be polished out. Pitting is corrosion that has started, and it usually begins where something has been sitting against the metal holding moisture.
The places to look are under clamps, under hangers and under any shield that traps road salt and dirt. Those crevices are where a stainless steel exhaust system can corrode while every visible section stays perfect. A pipe that looks immaculate but has a rough patch under a rubber is not a clean bill of health.
Rubbers deform to the load they carry, and by now they have taken a permanent shape. That is acceptable when the shape is symmetrical and the pipe still hangs where it should. It is not acceptable when a rubber has stretched long, when a hook rests on the edge of its mount, or when one hanger is clearly carrying all the weight.
Check the hangers with the car on the ground and the system at rest. A pipe that has settled lower at one end is a system that is not sharing load, and it will keep moving that way. Correcting a hanger is a small job; correcting a cracked pipe caused by an unsupported section is a much larger one.
A titanium exhaust system tends to look more dramatic at this stage because its colour change is more visible. It is also thinner and lighter, so it is less forgiving of a hanger that loads it in the wrong place. The colour is not a warning; a dent or a bright rub mark is.
Stainless is heavier and holds its shape with less support, so it hides installation problems for longer. The practical consequence is that a titanium system wants its hangers and clearances reviewed more carefully at this point, while a stainless system is more likely to show its problems later, once a loaded hanger has had time to fatigue the metal.
Some parts should look exactly as they did when they went on. Nuts should not have bright rings under their heads. Flange faces should not have soot fans on them. No hanger should be polished where it meets its rubber. Those three are the signs of movement, and movement at this stage is the start of a failure rather than settling.
Everything else can be allowed to age. The system is supposed to discolour, collect soot and look used. What it is not supposed to do is move where it was fixed. Judge the first long interval by the fasteners and the contact points, and keep appearance out of the assessment entirely.
