We have corresponded before regarding mass-air-flow (MAF) cleaning, by revving the engine up to 2,500rpm and switching off the engine, although it was at least a couple of years ago. I am still running my Mercedes-Benz C 250 Turbodiesel Estate (delivered new in February 1997, and now past the 250,000 mile mark). It is running superbly for its age and mileage, having been regularly serviced most of its life by Cobra Auto Services of Edmonton until just recently. I have now retired to Kent and my new garage, Red Oak Garage, an independent Mercedes specialist in Maidstone, said that it had been excellently serviced previously – quite a compliment from one garage about another. Anyway, the turbocharger is the original one, but is at last showing its age by leaking a little oil from its bearings, although otherwise performing excellently. I have been told that turbochargers can be refurbished for less than half the cost of a new one (£750 to £800), but would you recommend this action? I know the car will be off the road for longer than by just removing the old part and fitting a new one, but I can manage this by putting it into my local garage before I go on holiday, and it should then be ready when I return. The five cylinder in-line engine (Not many V5s around Terry!) has never needed to have its cylinder head removed for any work and I have only had to have replacement glow plugs and new injectors fitted, plus one new exhaust system and a water pump in all this time. I regularly use Millers Diesel Power, every 2,000 miles or so, which seems to have kept everything clean and tidy, a tip from Diesel car some years ago! I again look forward to your very good advice and your articles are the first items I read each time I get my Diesel Car magazine. Thanks for all the useful information you provide.
Terry Raynor, Maidstone

I remember the subject indeed, but not the name. Never mind, it is always very good and rewarding to hear from loyal readers. 250,000 miles with the C-Class – most impressive! Good maintenance in the past, as you say, and good to know that your new garage agrees. I’m publishing both garage names, old and new, as they both seem well deserving of some free publicity. Not forgetting credit to the Millers, of course. Turbochargers can indeed be re-manufactured, rebuilt, reconditioned, or what you will, at a far more economical cost than fitting a brand new one. So the principle is fine. But I would check out whether your new garage is going to send it away to a turbocharger specialist (it might not even be your original one that came back) rather than do it themselves, which I would not be too wild about, unless you know that they have specialist turbocharger experience. No offence intended to your new garage either, but it would be worth getting a quote from a specialist, such as Turbo Technics, or Turbo Solutions that you can find on the web, as a cross-check on costs. Did we ever decide whether the engine switch-off routine worked with Mercedes engines and MAFs?? Senility again I’m afraid!
Doctor Diesel

To which Terry replied: 

My new local garage have said that they would send the turbocharger away to a specialist to rebuild the turbocharger, so no problem there. Regarding the MAF sensor cleaning, yes it does seem to improve matters on the Mercedes when carried out about every 5,000 miles. I don’t do it more often than that as I feel the thermal shock of heating the sensor by this method may well reduce its useful life.
Terry