Low-load running and what it leaves behind
Almost all driving around Norbury town centre and up over Pollards Hill is low-load: London Road is a red route with constant signals and bus stops, Northborough Road is residential and speed-limited, and even the run out past Norwood Grove and Pollards Hill Park is stop and start. An engine in that traffic is making a fraction of its available power, with combustion temperatures too low to keep plugs and the inlet tract burning themselves clean.
Over a two-year interval that shows up at the plugs. Deposits build on the insulator, the electrode wears and the gap widens, and the ignition coil has to work harder each time to bridge it. The early symptoms are easy to live with and easy to misread: slightly longer cranking, a stumble as you pull away from the lights, fuel consumption drifting upwards. The late symptom is a misfire that puts unburnt fuel into the catalytic converter and ruins it.
At a major service we fit plugs of the exact specification your engine calls for, from NGK, Denso or Bosch, torqued properly, and we look at what the old set tells us about how the engine is running. On diesels the fuel filter takes their place where there is a serviceable one. The brake fluid is changed completely from a sealed container and moisture tested before and after, which two years of red-route braking makes worthwhile.
Everything in the full service is included, including the wheels off with pad and disc measurements recorded and a fault code scan across the control modules. Allow most of the day with us. The route down is the Pond, the Lombard roundabout and the A236 across Mitcham Common, about eighteen minutes, and collection and delivery can be arranged. Written quote first, and a 3-month workmanship guarantee on repairs.

