It is no secret that there are a significant number of failures on TDi turbos, particularly at Highveld levels and particularly on the Polo models. It is a known fact that VW replaces a lot of them, and that the reasons for their failures are often misrepresented. So here are some thoughts and suggestions for those who are either concerned or have had some experience with this problem.
First of all, let me clear something up which is a common misconception. The VNT15 turbo fitted to the PD motors is NOT a bad turbo, in fact the variable vane turbo fitted to the Polo is one of the best on the market. However, every part of a car is only as good as the conditions it works in, and there are a number of reasons which contribute to the failure of these units;
1.) Oil feed. The hoses that feed oil to and from the turbo are poor diameter and have limited thermal resistance to heat from the manifold, exhaust and turbo itself. These are often not replaced after turbo failure, even after a turbo repair, with the consequent result that the problem that caused the first turbo to go, may precipitate the same on another turbo. Heat causes the oil in the channels to carbonise, and often this carbon is drawn into the turbo bearings, ultimately causing wear & causing the shaft to break. Bearings are on their way out when you can hear a characteristic whine/whistle from the turbo.
2.) Although you will find precious little if anything in your owners manual, you should run your turbo down for 30 seconds around town and as much as 3 minutes after sustained high load running/ or long trip. This allows oil to circulate through the turbo. There is no auxilliary oil pump which operates after the engine runs down similar to that employed in the S3. Hot shutdowns may potentially precipitate 1.) above.
3.) Do not use poor quality oils or fuel. Make sure you see the right synthetic oil indiciated on your service invoice from VW. Also do not assume that all diesel is the same. There are currently only 2 low sulphur (Euro compliant) fuels on the market, and they DO make a difference.
4.) Tuning; Overboosting and overfuelling raises Exhaust Gas Temperatures in diesel cars, compounding the high ambient temps, less dense air (Highveld)and crappy fuels our modern generation high tech diesel engines have to cope with in SA. Make sure your tuner of choice addresses these questions before you commit to a chip. TDI's are very tuneable, but exercise caution. It is worth noting that turbos fail in both standard cars and modified cars, but a tuned car is more likely to make a weak link snap if it exists.
Running in decently is essential. Dont be tempted to over stress a new engine. It is tempting in an age when 1.9TDi's can embarass much larger performance cars, but respect the recommendations for running in and operation, and importantly do not over-rev a diesel, they do not like it.
If you are unfortunate enough to experience a failure on your TDI, check the following;
1.) ASk your dealer to assess the cause of failure, dont let him just swop the part with no explanation.
2.)Ensure that oil feed pipes are either replaced or thoroughly cleaned and inspected.
3.) Ensure that oil is changed along with the filter.
4.) Do not over-run the turbo for the first 1250km after replacement, use no more than 2/3 throttle.
They are great cars, properly cared for your TDI will respond well to the basic care outlines given above, even if your dealer doesnt advocate them all. Love your VW
