Volvo B4204S / B6304

Volvo's modular petrol engine in its four- and six-cylinder forms — the 2.0 B4204S in the S40 and C70, the 2.9 and 3.0 B6304 in the S80 and S90.

They are one architecture with a different number of cylinders, and the five-cylinder version — the white block that most people mean by a Volvo engine — has its own page here. All three share their bore spacing, their head design and most of their faults, so results from the five usually apply.

The recurring items are ventilation and ignition. The crankcase ventilation system blocks, pressurises the crankcase and pushes oil past the seals — the classic Volvo oil leak, and it is a maintenance item rather than a failure. Ignition coils fail one at a time.

The timing belt is an interference design and drives the water pump; on the six it is a longer, more expensive job than the four, which is worth stating before a quote is given.

The B6304T turbocharged six in the S80 is a different proposition from the naturally aspirated engines and its boost plumbing is where its own faults live.