2004 Mazda 6 2.0L Petrol · R5 OKE

The first-generation Mazda 6 GG/GY suffers from notoriously poor factory corrosion protection and thin underbody seam sealant. In the wet and salted UK road climate, road grime and damp mud become trapped inside the folded metal lips of the rear wheel arches and behind plastic underbody shields. Rust starts from the inside out, bubbling through the rear quarter panels, consuming the structural sills, and rotting the rear suspension mounting crossmembers and front subframe legs. Unchecked corrosion compromises crash structure integrity and results in extensive structural MOT failures, requiring expensive bespoke metal fabrication and welding to rectify.

On 2.0-litre CiTD common-rail diesel models, the copper injector seat crush washers can fail over time, allowing high-pressure combustion blow-by gases to escape past the injectors into the engine oil gallerias. The escaping hot carbon rapidly carbonises and sludges the engine oil. When the oil circulates, these baked carbon particles are drawn into the oil sump, where they completely choke the fine wire mesh of the oil pump pickup strainer. Oil pressure drops catastrophically without warning, leading first to turbocharger bearing seizure and subsequently to total crankshaft and engine failure. Routine sump removal and injector resealing are essential preventative measures.

First-generation Mazda 6 models—particularly the higher-torque 2.0 CiTD diesels and 2.3-litre petrol models—are prone to accelerated clutch plate wear and dual-mass flywheel (DMF) degradation. Drivers encounter a stiff, heavy clutch pedal, clutch slip under hard acceleration in higher gears, and prominent vibration or shuddering when pulling away from rest. In addition, the clutch release bearing can fail prematurely, producing an audible squeal or rattle in neutral that disappears when the pedal is pressed. Replacing the clutch on the transversal layout requires subframe lowering, making labour costs significant.