Dear Doctor Diesel,

How do turbochargers get contaminated with whatever they do, for the vanes to get stuck? The air enters via the air filter and then arrives at the turbo to proceed to the inlet manifold via the intercooler and EGR. I am at something of a loss as to where the awful muck that can clog the turbocharger comes from. Is there any device between the air filter and the turbo? I cannot see one on my car, Astra 1.7 CDTi, 2006 registered.

Regards,

Peter Duffy

Well Peter, you certainly got me thinking about this, and in particular how turbocharger cleaning fluids work, which I had not thought about before. Firstly though, the vanes on a variable geometry turbocharger are on the hot side of the turbocharger, where the vanes being driven by exhaust gases, which obviously can have particulates, oil mist and other things in them. It is these exhaust products that can clog up the variable angle vane actuation, usually as a result of the engine being in poor condition, due to age and mileage, or poor combustion, or use of lower quality fuel. So that side is totally unrelated to the intake gases. The driven turbo that handles the inlet gases will generally stay pretty clean, due to air filtration, but with some danger of contamination when crankcase gases are recirculated, and I believe that on some engines (possibly HGV engines and other larger diesels), the crankcase gases are filtered. The EGR (Exhaust Gas Recirculation) gases, at high pressure, are fed via a throttled EGR valve into the inlet gas flow after the boost turbocharger rotor and intercooler, so they won’t contaminate that side of things.

Increasingly though, engine designers are using “low pressure” EGR though, where the cooler exhaust gases are drawn from further along the exhaust gas route and fed back into the inlet gases somewhere around, or before, the boost turbocharger. They are, by then, cleaner and far less damaging than hot exhaust gases, and therefore help to reduce emissions compared with high pressure, high temperature EGR. Today’s EGR systems generally seem to use hot/high pressure EGR from start-up, to aid engine warm-up, and then phase over to low pressure/low temperature EGR when the engine reaches normal running temperature.

What got me thinking, though, was how turbocharger cleaners work, since they involve liquids being fed into the air intake, when they then have to get all the way through the boost turbocharger rotor, and pass through the combustion chamber, before they can do anything at all about cleaning the exhaust side turbocharger and its vanes. Having asked myself this question, I found an answer as follows, from the turbo cleaner product “Revive” that advertises in Diesel Car:

ìUnlike flammable propellants, which combust and are spent by the time they reach the hot side of the turbo (turbine), Reviveís patented non-combustible formula survives the burn process, and the ingredients are still active passing through the exhaust valves and turbocharger, ensuring an effective clean of the variable vane mechanism.î

So, there you have my explanation, for what it is worth!

Best regards,

Doc Diesel