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30K oil change interval: will it ruin your engine?

18/11/2013 06:32 | Comments: 
Recommended maintenance intervals have become an important selling point in the new car market. Modern engine mechanicals and the advances in tribology (the study of friction and lubrication) have by now allowed for far longer oil change intervals than the previously customary 5-10 thousand kilometres. Or have they?

Recently I have written numerous articles about engines, prompting me to turn my attention to other subjects. However, this issue is potentially relevant to an immense number of car owners so I cannot keep this to myself any longer.

There was this 2009 Mini Cooper S brought in to my garage, with the now known symptoms of jerking. It was not only Mini owners complaining of the stutter but also owners of Peugeot and Citroën cars equipped with the 1.6 turbocharged petrol engine.

This error entails that if engine knock exceeds a certain threshold, the ECU will temporarily shut down the injectors to remedy the symptoms. This causes the car to jerk and stall to a degree that makes driving this otherwise perfect little car both unpleasant and dangerous. I have often commented on how direct injection engines are prone to be plagued by soot deposits, which is also what we were facing in this case. While in case of another Mini I was able to remedy the fault by replacing the ignition transformer a while back, unfortunately the symptoms kept recurring after only a few months.

The customer also complained about a chatter in the engine so I decided to partially open up the engine. I have seen my fair share of engine horrors but there was no preparing for this one. Everything under the cylinder head was covered in sludge at least half an inch deep.

The car is four years old, with the odometer at 62 000 km. The engine has had two regular inspections with the second one completed merely 2000 km ago.

Whoever came up with the idea of extending the servicing interval of a turbocharged petrol engine to 30000 km certainly didn't have a degree in engineering. On the other hand, this sludge deposit could be the result of some material – such as petrol – entering the chamber. It could have been introduced by the high pressure fuel pump driven off the camshaft, however there is no proof supporting that theory. The oil did not smell of petrol, and there was no obvious increase in oil level.

I checked the timing chain with a specialised tool. Unfortunately the stretch was beyond the threshold. Here is a video showing you how this test is done.

I borrowed an endoscope from a business partner and checked the piston crown. Just as I feared: there was soot deposit within the combustion chamber. This is not an aesthetic issue like kids stashing their half-eaten donuts behind their seat and you need to apologise to the vacuum guy at the car wash. No, this is dead serious and highly detrimental to the operation of the engine. As soot particles heat up and glow they can ignite the mixture and cause uncontrolled combustion. The knocking you hear can be caused by the flame fronts colliding, which is probably what caused the initial symptoms.

This is a regular road engine with a specific output of over 100 PS/litre. Two decades ago those figures would have indicated a race engine. In such a high strung system even the slightest imperfection can cause engine failure. This is a common error pertaining to all modern engines: they have absolutely no tolerance to even the tiniest deviation from ideal operating conditions.

In this system both the spray pattern and the direction of the injection are decisive parameters. The red arrow in the picture indicates a thick deposit of soot on the injector

It is plainly visible that the cross flow of the intake ducts has been reduced. This might not be such an issue on a charged engine except direct injection means it is crucial that intake air enters the combustion chamber with the right swirl.

Sludge has very little sympathy for our pocket. It has found its way to the turbocharger which has miraculously survived the insufficient lubrication caused by the soot-clogged oil channels. What was critical is that the car had just been through a proper maintenance which was done, however, in a highly improper fashion, as the factory does not require the inspection of the lubrication points for the turbocharger.

This engine comes with an adjustable camshaft dubbed Vanos. Whenever I hop in a Mini I get this uncontrollable urge to own one, and Vanos is one reason for this desire. This system provides for perfect scavenging, as you need different camshaft angles at low and high speeds, enabling the engine to yield maximum torque in the widest possible rev range.

Vanos has fairly simple mechatronics. There is a PWM-controlled magnetic valve (1) allowing a certain amount of oil, as determined by the ECU, to flow through a channel (5) into the camshaft (2) . At the contact point (3) this oil flows from the camshaft into the variable control wheel (4) which rotates the camshaft in relation to the timing chain and hence, the crankshaft. The degree of rotation is determined by the chambers.

If you want to keep the total cost of repairs reasonable you might want to try and look for shortcuts. That of course does not mean you should go with anything less than factory quality but you can and should double check your sources. I called an authorised BMW/Mini repair shop and nearly dropped my phone when I heard their quote. I had to go a different route. Obviously this engine has been co-engineered and co-produced with PSA so I should be able to acquire the identical units from the realms of Peugeot spare parts supplies. And I did.

Because the timing chain was stretched beyond the threshold I installed a brand new timing set after cleaning and re-installing the cylinder head. This job absolutely requires a specialised tool set.

This engine is pretty easy to service compared to other contemporary powertrains except it takes a lot of time. You also need some significant experience, but you can acquire that fairly quickly: I have disassembled two of these engines within a week, although the other one had run some serious 142K.

Following a thorough clean-up and reassembly you could easily feel the power returning to the engine. The jerking has gone, too. I believe it is important that regular maintenance goes beyond changing the oil. Talking about this specific engine it would be important to replace the tubing of the turbocharger as soon as you notice the kind of contamination you can see above. Based on my subjective judgement the only thing the 30000 km servicing interval is adequate for is to postpone the death of the car beyond the end of the warranty period.

Is there anything you can do to prevent soot build-up in the combustion chamber? PSA does require the use of an additive that simply needs to be poured into the fuel tank every couple thousand kilometres; this will prevent deposit forming. It will probably not be able to remove the soot already there but you can use it as a preventive measure.

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