Know your turbocharger

Replacing a turbocharger is an expensive business, but understanding how it works and how to look after it can massively increase its life, as Ed Evans explains

APROPERLY used turbocharger can be expected to last the life of the engine, assuming the engine itself is correctly maintained. And that’s quite a result, considering turbochargers were never designed with any direct maintenance in mind. Even on the increasingly complex turbochargers fitted to later engines, there is still no prescribed maintenance for the turbo and, in many cases, no possibility of accessing it if there was. In theory, they’re a fit-and-forget component. In practice, they can fail in a variety of ways.

With early turbos we can often work out the problem, maybe fix it, and certainly renew the turbo ourselves. On later electronically controlled versions it’s a different matter. I recently had to replace the turbocharger on my Range Rover Sport because the dashboard message centre effectively told me to, but more of that later.

The first Land Rovers to be fitted with a turbo were the Ninety and One Ten 2.5Td (turbo diesel) models, and that was something of a disaster because the bottom end of the old 2.5-litre engine wasn’t up to handling the extra performance from the turbo. That was the only problematic engine in respect of its turbo, and Land Rover turbos have since evolved from basic mechanical units into electronically-controlled modulated systems that change output to match the driving demands of the moment. Turbos aren’t so much a performance booster, as an efficiency booster, which is why every

diesel has one, and it’s now also common to see them on petrol engines.

It’s basically a turbine driven by the engine’s exhaust gases which, in turn, drives an air compressor that charges (or increases the pressure of) the air going into the engine.

Putting air into the engine at a higher pressure has a simple and direct effect on the performance. Before an engine cylinder fires, diesel fuel and air are compressed in the cylinder, creating heat that ignites the fuel. As the fuel-air mix explodes, the resulting expansion of the gas forces the piston down, thus turning the crankshaft. With a turbocharger fitted, the initial air charge in the cylinder is at a higher pressure so, after the explosion, the gas tries to expand even more. Of course, the gas can only expand within the confines of the cylinder, so it simply drives the piston down with even more force. This is one of the reasons why turbocharged diesels have masses of torque at low engine speeds – ideal for heavy towing and off-roading.