A soldered seam on an exhaust cannot survive the gas temperature or the vibration. Why the process fails on principle, and what a sound repair looks like instead.
Brazing melts the filler, not the parent, so it suits thin walls and dissimilar metals but not load or heat. How to judge which joining process a given part actually needs.
How cleaning products leave films that read as faults, solvent and spray residues compared with carbon, oil and coolant, and the heat cycle test that separates them.
Why water at the tailpipe causes so much confusion, what condensation and coolant each leave behind, the smell test, and how the expansion tank settles it.
How a bend throws the flow outward, why the outer wall collects a band, what a heavy band says about velocity, and when the bend itself is the problem.
A clean bore is a reading too: the washed look left by a fluid leak, the honest clean of a healthy engine, cold metal, and clean zones behind a restriction.
