Mazda 6 2.0 CD GH

This is the RF7J engine's most serious design flaw. The original triangular-shaped copper injector seals deteriorate over time, allowing hot combustion gases past the seal into the camshaft area. These gases cook the engine oil, producing hard carbon deposits that circulate through the oil system. Eventually these deposits block the oil pump suction strainer, starving the engine of oil pressure. Symptoms include rising oil level (fuel dilution from DPF regens), low oil pressure warning light, and in severe cases catastrophic engine damage. Mazda issued a technical bulletin and revised the seal design in 2014 (tinned copper washers with a new tightening procedure). Repair involves removing injectors, cleaning pockets, fitting new seals, and cleaning the oil strainer. If caught early this costs around €800-1,200. If the engine has sustained bearing damage from oil starvation, a rebuild or replacement can reach €3,000-3,500. Any used GH diesel should have the revised seals fitted as a minimum.

The 2.0 MZR-CD's DPF management is widely considered poorly executed. Unlike most competitors, the Mazda 6 GH does not display any indication that a regeneration cycle is in progress or needed. If the car is switched off mid-regeneration, the process stops and unburned fuel washes past the piston rings into the sump oil. Over time this raises the oil level (check the dipstick for overfilling) and dilutes the oil's lubricating properties. Cars driven predominantly on short urban trips rarely complete a full regen cycle. Professional DPF cleaning costs €250-400, while a clogged unit needing replacement runs €1,000-2,000 including fitting. Using the correct ACEA C1 low-ash oil is essential, as standard ACEA C3 oil generates more ash and accelerates clogging.

The variable nozzle turbo uses small internal vanes to regulate boost pressure. Over time, especially with gentle driving and short trips, these vanes become coated in soot and carbon from the exhaust and can seize. Symptoms include loss of boost below 2,500 rpm followed by a sudden surge of power, EPC/engine warning lights, and limp mode. In some cases the rivet holding a flap on the turbo actuator fails. If caught early, a turbo clean (removing and manually cleaning the vanes) costs around €400-600. If the turbo internals are damaged or the actuator has failed mechanically, replacement runs €1,200-1,800 with a reconditioned unit. Regular spirited driving that keeps the engine above 2,500 rpm helps prevent carbon buildup on the vanes.

When injector seals leak and oil becomes contaminated with fuel and carbon particles, the exhaust camshaft lobes suffer accelerated wear. The cam follower material on certain production runs was also harder than ideal, contributing to the problem. Worn exhaust lobes mean the exhaust valves do not open fully, causing poor fuel economy, reduced power above 4,000 rpm, and hesitation. Metal fragments from the worn camshaft can also damage the vacuum pump seals and enter the turbo bearings. Repair requires camshaft replacement, which involves significant labor. This issue is almost always a consequence of neglected injector seals and contaminated oil, so cars with documented seal replacement and frequent oil changes are at much lower risk.

The diesel model uses a dual mass flywheel to absorb drivetrain vibrations. These wear gradually, producing a rattling or knocking noise at idle that disappears when the clutch pedal is pressed. The DMF cannot be resurfaced and must be replaced. Parts cost €400-600 for an aftermarket unit (LuK or Sachs), with labor adding another €400-600 due to the complex gearbox removal procedure. Most specialists recommend replacing the clutch disc and pressure plate at the same time, bringing total cost to €1,000-1,800. Typically needed between 120,000-180,000 km depending on driving style. Urban stop-start driving accelerates wear.

Carbon buildup on the EGR valve is a common issue on the MZR-CD diesel, particularly for cars used on short trips. Symptoms include rough idle, hesitation on acceleration, and occasional stalling. The Mazda 6's EGR valve can usually be cleaned rather than replaced, which saves considerable money. However, removal and cleaning takes several hours of labor due to accessibility. Cleaning costs €200-300 at an independent garage, while replacement with a new valve runs €400-500 fitted. Most owners report needing EGR attention every 60,000-80,000 km.