Mazda Mazda6: GG/GH Rear Wheel Arch and Sill End Rust Perforation

The rear wheel arches and rear sill ends on GG and GH Mazda6 models suffer from accelerated corrosion caused by road debris trapping moisture against the inner arch lip and the sill drainage channels blocking. Rust initiates at the factory seam welds on the outer arch lip and progresses inward through the wheel arch liner. The rear sill ends (behind the rear wheels) also perforate at the drain hole area. This is a cosmetic-to-structural progression: early cases are panel rust, but advanced perforation compromises the rear floor and sill box section which forms part of the side-impact structure.

• Bubbling or lifting paint along the rear wheel arch outer lip, often first appearing as a blister line following the seam weld
• Orange rust staining visible through the wheel arch liner from behind
• Perforation holes at the lower rear sill end, sometimes hidden under plastic trim caps
• In advanced cases, audible creak from the rear body when the car flexes over a dip, indicating sill box section compromise

1. 1

   Look for bubbling paint, rust staining through the arch liner, or perforation holes.

2. 2

   Inspect the rear sill end caps and the lower sill panel immediately behind each rear wheel for bubbling, flaking paint, or holes.

3. 3

   Press on any suspect areas with a gloved thumb — a crunching sensation indicates through-rust.

4. 4

   Check drain holes in the sill for blockage and standing water.

5. 5

   If a workshop inspection is possible: Remove the rear wheel arch liners (if fitted) and inspect the inner arch lip seam weld with a torch and probe.

Parts involved: Body corrosion.

$500 to $3,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Can I remove the rear wheel arch liners during inspection to check the seam welds?”
• “Has the car had any rust repair or underseal treatment done on the rear arches or sills?”
• “Has the car been garaged or stored outdoors in a coastal or high-rainfall area?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.