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What makes turbochargers die?

Turbo failures, bad designs and careless users

31/07/2013 08:07 | Comments: 


Former car restorer, damper designer, rotary-engine guru and also an automotive engineer, but generally doesn’t talk much about his former activities. András is our mag’s Leatherman tool: when there’s a project no-one would poke with a stick, he’s the one usually assigned to carry it through. When he’s in Hungary, he works 16 hours daily, then every once in a while he disappears from the horizon. Last time he’s been seen in Auckland… Has a huge garage, lives with a girlfriend.

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Even ice balls can cause turbocharger failure, but in most cases lack of lubrication is the reason. How can we prevent it?

When I fixed an appointment with Ferenc Jäckl, owner of probably the biggest turbocharger repair shop in Hungary, I had no idea what secrets he'd disclose, what he would be willing to show. But if he would just guide me around his workshop and tell some stories about turbocharger failures that happened during all those years he's been in the business that would be more than enough for me. In fact, we would be more informed about that spinning wheel under the bonnet of their motor vehicle than about a 100% of the so-called consumers.

This is the authorised turbocharger repair shop of Porsche Hungaria, Renault, Peugeot and Citroën in Hungary, an official Mitsubishi and Borg Warner partner with more than ten thousand overhauled turbochargers by now - as I walked into the entrance hall of Ferryker, I knew I was in the right place. Even those who are not officially teamed up with them, bring their turbochargers here, because they can fix any size of turbocharger from a Smart car to huge power plant engines. And if repair is out of question, they will get a new one. Indeed, they have accumulated vast experience over the last fifteen years.

As a greeting, I get a brand new sliced-up BMW turbocharger in my hands from Ferenc, and he immediately starts to point out the important things. This one has a billet compressor wheel, milled from one piece, therefore it won't explode as easily as the old-type cast ones. All right, we've already been thrown in at the deep end. Small imperfections, inclusions are always present in castings, so if the wheel is overrevving for any reason - not mentioning chip-tuning - you'll be busy for a few hours cleaning up the aluminium chips in the intake pipe of your engine.

Turbos traditionally have a bad reputation. Everybody is afraid of them, because replacement isn't cheap. If something goes wrong with the engine, the turbo is blamed most of the time. The truth is, however, that most turbo failures happen as a result of some kind of engine problem. In 90% of the cases insufficient lubrication is the reason, says Ferenc self-confidently, and that means it's not the poor turbo's fault at all. Clogged oil passages, contaminated engine oil or unprofessional repair attempts cause the oil circulation to collapse and the small bearings to not get proper lubrication any more. That means the end of the turbocharger.

The other significant problem is insufficient knowledge. Although the biggest enemy of the turbocharger is still the mechanic, the user himself can easily do some fatal harm to it.

One can argue that you don't have to be an expert of quarks and gluons if you want to switch on the light in the kitchen, but in the last few years the invasion of turbo engines brought this sensitive technology to millions of users. To users who wouldn't recognise a turbocharger even if it came up in their soup. It's not their fault, I also couldn't tell the difference between rye and barley, but at least I won't go harvesting. On the other hand, if you're driving a turbocharged car - and that's very likely if it's one of the newer types - you should know at least some basic stuff.

I'd say car manufacturers carry a huge amount of responsibility, because they spread the belief that the car is there to do its job and we don't have to give a shit. They even mention on page 362 of the owner's manual in small letters that it might be a bad idea to kill the engine immediately after a heat on the motorway, if you want your turbocharger to live long, but people tend not to read the owners manual. They prefer to use their vehicle in any way the vehicle tolerates it. If you can go flat out with a cold engine, they will do that.

When does the turbocharger switch on ?

As long as I can hear sentences like ”just try to open the glove box when the turbo switches on”, I feel it's necessary to explain how the turbocharger works. It's not very complicated, anyway. Those who know can skip the next five paragraphs.

The principle is quite simple: we use the energy of the exhaust gases which exit the engine at a great speed to squeeze in more air into the combustion chambers than the motor could suck in normally. You can then mix more fuel with that extra amount of air (you know, fuel particles need oxygen molecules to burn). This makes the engine stronger and more efficient, so a good turbo engine not only has a smaller displacement, but also consumes less than a naturally aspirated one of comparable size.

From a technical point of view you can imagine a turbocharger as two wind turbines, accidentally mounted on the same shaft. As one turbine gets the flow of the exhaust gases, the shaft starts to turn quite quickly and the other turbine acts as a ventilator and blows air into the intake pipe of the engine. There's no switch or anything like that – when we start the engine, both turbines start to rotate continuously, since the exhaust gases are driving one of them. The thing that matters is the speed of the rotation.

The strong push that you feel when the turbo kicks in happens when the turbocharger starts to rotate at really high speeds and pushes considerable amounts of air into the engine. For some physical reasons the ventilator (compressor wheel) only works well when the shaft reaches a certain speed. That happens when the turbine wheel gets a strong flow of exhaust gases.

Modern turbos wake up at about 1500-2000 rpm and from there on the engine goes wild. The tiny little turbine only needs a certain amount of clean and cool oil to stay happy. We should however respect this need greatly, because in reality a miniature apocalypse is happening inside, every day. Exhaust gases are not as friendly at a distance of about ten centimetres from the engine, as they are at the end of a four metre long pipe. Flames are hitting the turbine wheel, aggressive pressure waves try to demolish the blades like machine guns, and in one minute, gases with the volume of an average kitchen, exit through the teacup-sized propeller at temperatures of several hundred degrees. The shaft can rotate at speeds of 200,000 rpm – in comparison a good washing machine does 1000, a domestic drill about 2000.

For this hell of a job it only gets a shaft as thin as a toothpick, which is rotating in a bronze bearing as small as my little fingernail. The axial forces are taken up by a piece of metal not much bigger than the end of my thumb. Most of the turbochargers don't have extra water-cooling, so at high loads they can get red hot. Considering all this, you can imagine how important it is to supply the little bearings with nice, fresh oil through a straw-sized pipe. If this straw gets clogged or some dirt gets into the bearing, the small shaft rotating at a devastating speed can destroy its surroundings quickly. If you're lucky, only the bearing will get damaged - in this case the turbocharger can be repaired. If the shaft breaks, you'll need a new turbo.

Don't panic though, first let's talk about how to avoid the catastrophe. The old-school wisdom still holds true, however turbo technology has advanced a lot in the last few years. Harsh driving with a cold engine and killing the engine after going flat out still hurt the turbocharger. So after starting the engine, it's a good idea to wait a few seconds until proper oil circulation has started in the turbocharger, and it doesn't hurt to drive carefully on the first few kilometres, either.

But it isn't wise to be overly careful – if you always change gears at 1500 rpm you don't protect your engine. At extremely low revs there is no proper oil pressure, so even if the turbocharger is spinning at idle speeds, the lack of lubrication causes some considerable wear. Turbochargers with variable geometry suffer from another problem if not driven properly: the vanes that direct the exhaust gases to the turbine wheel can build up carbon deposits until they can't move any more. Those turbochargers need some flat out driving from time to time so the deposits can be burnt out.

Death by heat can happen when switching off the hot engine. After hard motorway driving the turbocharger can be red hot - if you don't give it time to cool down and turn off the engine, the cooling oil flow stops and the lubricant gets burnt inside the bearing. Pay no attention to these recommendations and soon you'll have to get an appointment with your turbo-doctor.

You shouldn't be envious about the turbocharger repair shops, even though they have been doing pretty well in the last few years. They get a simple-looking but highly sophisticated part from the dirty hands of a mechanic and have to give it back after a few hundred euros/dollars spent on it, wishing it farewell. If you've ever tried to give advice to a below-average car mechanic, you know it won't be easy.

Although Ferryker is mostly connected with authorised workshops and serious mechanics, they still have to dedicate the front page of their website to the very basic information needed to properly replace a turbocharger. In addition, they put a big red sticker on every repaired turbocharger, but apparently this is not enough: it still happens that some customers return after a few days in the hope that they'll get their money back.

After getting the turbocharger in his hands the specialist can usually determine that the failure was not the turbo's fault within 30 seconds. But then he'll have to fight with the mechanic for minutes to convince him to repair the external fault that caused the death of the turbo in the first place. And only after this job is done can he put back the repaired, overhauled or new turbo. Even the simplest thing - namely to change the oil and the filters before removing the broken turbo – is difficult to explain to many of the lads. They tend to do this after they have replaced the turbocharger. Bad idea.

Ferenc who used to be in the car repair business for about twenty years before opening his turbo shop, is dedicated to spreading the word. He gives lectures whenever he's invited, and he even thinks about giving some lectures on his own site. In fact, he wants to make his own job easier, since he's the one who deals with warranty issues. If he can avoid just a few turbo faults caused by unprofessionalism, the effort has paid off.

However, the most useful info Ferenc can provide is which are the bestsellers in his shop, so which models you should avoid when choosing your next ride. Ferenc has documents about every repair in his shop, so after a short breath he starts the list: Fiat's 1.3 Multijet and the Peugeot 1.6 HDi have been the two most problematic engines in the last few years, but the 1.9 Renault dCi isn't flawless, either. When the turbocharger of a 1,8 Audi engine arrives at his shop, it's not hard to tell why the failure happened, and certain BMW engines also have some common problems. Let's go down the list, point by point.

Besides Fiats you can also find the 1.3 Multijet diesel under the bonnet of some Opel/Vauxhall Corsas and Suzukis. This engine is not everyone's cup of tea because of the noise it makes, but even those who like it will be upset when stopping at temperatures under minus ten and starting next morning. Under these conditions, it's very likely that small ice balls will build up in the pipe just ahead of the turbocharger. After starting the engine, the compressor wheel will suck them in, causing the blades to bend. The design was changed on later models, but those who have an early Multijet and are parking on the street had better not start their engines in the morning if it's really cold.

The 1.6 HDi has a much nicer sound, no wonder it's such a popular engine. They use it not only in Peugeots, but also in Citroëns and Fords. Such a shame, it turned out lately that the turbos tend to go kaputt already at around 60 thousand kilometres. The 90 PS version has an actual design fault. The oil feeding pipe of the turbocharger has a banjo bolt with a tiny little filter in it, which usually picks up the dirt and gets clogged. If the turbo doesn't get sufficient oil, it'll obviously fail sooner or later. The record holder at Ferryker managed to get as far as 400 metres with a new turbocharger.

Then you can start again from the beginning. Because of that bloody small filter! Imagine how happy you'd be if that happened after the warranty had expired and the mechanic hadn't known about that problem. You pay for the new turbocharger, assuming it'll last at least as long as the previous one and then, after a few hundred kilometres you have the same problem again. This is what I mean about the lack of information. And again, this is another problem that's not the fault of the turbocharger. It's a bad design and the poor turbo is the weakest link.

It's a similar story with the 110 PS HDi. There, the 3.5-litre oil sump of the engine is just too small. Who knows why? Maybe they wanted to save on the service costs. Today we know that 3.5 litres is just not enough for this engine to provide good lubrication at all times. Guess which part will be the first to give up. Yep, it's the turbocharger again. There was no recall for this model, but the information sheet of the manufacturer reveals that if a turbo happens to fail, the oil sump and the associated parts have to be replaced, by one with a capacity of 4.5 litres.

Recirculation can be a problem with BMWs where the crankcase ventilation system doesn't let through the bigger volume of blow-by gases of worn engines. A clogged ventilation filter or a stuck bypass valve can lead to higher than normal pressure in the crankcase. If that happens, the pressure doesn't let the hot oil from the turbo to run back to the sump and the turbocharger will fail in a similar way as in the case of the HDi. Another example of bad design and an innocent turbocharger!

Not only the back-bleeding pipe but also the pressure pipe can cause problems, especially in petrol engines. In Audi's 1.8 petrol turbo for example, the pressure pipe runs directly underneath the exhaust header, protected by a heat shield. When that heat shield starts to decay with age, the header will inevitably burn the oil in the pressure pipe. In some severe cases, the burnt oil blocked the oil flow almost completely. No wonder the turbocharger failed.

At Renault's 1.9 dCi degraded parts of the airflow meter or the crankcase ventilation system can get into the turbo, leading to premature failure. The list of design misdemeanors of the engine manufacturers is long, but there's also an exception that proves the rule. Ferenc shows a design problem of a turbocharger where a spring which was too weak caused excessive wear at the bearings. This one was quickly rectified by the turbo manufacturer, and by now you won't get those faulty turbos any more.

The most upsetting turbo failure is, by the way, when the turbocharger itself is fully functional, but you still have to replace it. In many modern turbos the variable geometry vanes are controlled by a small electric motor through some little cogwheels. This little box on the turbo regulates the charging process, and if it fails, there's no repair kit to fix that, you have to buy a new turbo. I've seen some workshops where they can replace the small motor, but that's a task for the serious hackers.

The repair process for passenger car turbos is not very interesting, I'd say. The huge turbocharger of a power plant engine is more of a challenge, says Ferenc. A new compressor wheel has just arrived for such a turbochanger, so he opens the box and shows me the dotted code on this part which is worth more than 5000 Euros. The marking is vital, because the Chinese can copy even whole turbochargers. Luckily, at closer range they don't resemble the original ones - the person who imports them to Hungary, sells those with the advice to balance them before the first use.

A normal turbocharger fault that only needs a repair kit – that means the shaft, the case and the wheels are unharmed – is a few hours' routine job at Ferryker. That costs about 200 Euros, about half of which covers the price of the repair kit. Disassembling, grit blasting, cleaning and putting together is not a big deal, but amateurs can make huge mistakes even here. Ferenc has a collection of DIY turbo parts, he has a weakness for those infantile repair attempts. But even those who can put together a turbo at home will face the problem of balancing. That's the most important part of the repair process. The centre section balancing machine is the favourite one of the shop owner, there are not many of those in the country. But he also shows the old, analogue instrument which was a big thing when he started his business in the 90's. They still use it sometimes.

As always after visiting a specialist repair shop, I start the engine of my own car with great fear and trepidation. Now that I've heard at least a dozen horror stories, the question arises: how long will my turbo last? Then I remember that doctors always see the sick, never the healthy. I asked Ferenc to tell me about the bad examples, not about the turbochargers that live forever. But the conclusion of all this is that the turbocharger of a well-designed engine can truly live forever if one takes good care of it.

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