Volkswagen EA837 (3.0 TFSI supercharged)

The Volkswagen Group's supercharged 3.0 V6 — a Roots blower sitting in the vee rather than a turbocharger — in the Audi S4, S5, A6, A7 and Q5, and the Porsche Cayenne and Panamera. Its turbocharged successor of the same displacement is the EA839.

The supercharger's cooling is a separate circuit with its own pump, and it is the fault that reads as nothing at all. When the pump or the intercooler coolant is neglected, charge temperature rises, the engine quietly pulls timing, and the car simply feels flat — no code, no noise, no smoke. A 3.0 TFSI that has lost its edge is that circuit before it is anything expensive.

The thermostat and water pump are a single plastic module driven off the timing chain, at the back of the engine. It fails, and reaching it means removing the supercharger. The part is inexpensive and the job is not, which is why a coolant leak on one of these produces an estimate that looks like a mistake.

The timing chain and its tensioner wear on earlier engines, and being direct-injected it deposits carbon on the intake valves at mileage — the ordinary consequence of the design, and the reason a rough idle at 80,000 miles is often a cleaning job rather than a fault.