Some people say to beat it hard, some people say to keep turbo engine under boost to get the rings to seat, and some people say to treat it how you intend to run it. My opinions on this page are the same general advice from automotive engineers and the owner's manual. It's your engine and your car, so like any other internet advice, take it with a grain of salt and figure it out for yourself.
The "run it hard" opinion hit a resurgence with a website from an air cooled motorcycle mechanic. Aside from the page being focused on motorcycle engines, his hard break in technique for the street only takes the bike up to 65 mph - that's fast for a bike but not much for a car. Bikes are also thousands of pounds lighter than cars so the engine doesn't have to work very hard if you're driving "normally". Some of the misunderstanding is that one person's babying is another's beating. The advice also says that the critical window of opportunity is only 20 miles or 9 dyno runs, then it becomes 200 miles for the street - which is it? It also says that power loss from an easy break in could be up to 10% while the gain in power as a result of using his break in technique could be up 10%. Call me a skeptic: car makers have done full price + taxes buybacks when horsepower was 5% lower than advertised (RX-8) and it's well known that many engines are underrated in their actual power (335i N54).
The engine in your new car really isn't a brand new engine either - it was already tested at the factory, had its first oil change, driven on a dyno at the factory, on/off the transport, and then around the dealership. In some cases the car was driven to another dealer and test driven by other people. Some high performance cars are even driven hard on a track at the factory for quality control. If the first minutes of engine break in determine the rest of engine life and performance, you already missed it.
Engine break in goals are proper heat cycling, mating of parts, and stress reliving accomplished by incremental increases in varying rpm and load. You definitely don't want to baby the engine but you don't want to beat it hard either. The most important goals are avoiding excess engine wear, idling longer than you normally would, steady rpm, and high load on a cold engine. Let's look at the various parts of an engine and drivetrain to see how they are affected.
Clutch - Everyone will tell you that the clutch should be driven in moderate stop and go conditions for the first 500 miles with no excessive slipping. This transfers a layer of bedding material on the clutch, flywheel, and pressure plate, and prevents glazing from excessive heat and slipping. Holding a car on an incline using the clutch is really bad for the clutch and shouldn't be done even after break in. This wears the clutch disc for no reason and can contribute to excess heat and "hot spots". The outer diameter of a clutch and flywheel disc travels more distance in one rotation than the inner diameter (because it is farther from the center and travels in a larger circle), and the disc could, in extreme cases such as drag racing, promote warping and create an uneven friction surface. See 1000q: clutch FAQ for details on the TDI clutch/flywheel. On a side note, aftermarket stronger clutch kits/pressure plates could result in more crankshaft thrust bearing wear. Check the above article for an explanation.
The journal bearing turbos in your TDI float on a layer of pressurized oil. The turbo wheels can spin at speeds beyond 100,000 rpm and although it's spinning pretty fast at engine idle, it's still slower than if you're racing the engine. Early TDI are conventional fixed geometry and later/new TDI are variable vane turbos. See 1000q: turbocharging for more details.
These are precision machined and/or polished parts and require no special break in other than stress relieving through heat cycling associated with the rest of a normal engine break in (varying rpm/load, etc.) Flat tappet lifters should be broken in by varying the engine rpm around 2000-2500 rpm for a half hour but this really applies only to brand new engines with flat tappet lifters. Your new car already had this done at the factory. This is one reason to avoid excessive idling.
This is the major source of controversy. First ask yourself how many correctly maintained and operated water cooled car engines (excluding engines with known build quality issues) are replaced because of cylinder glazing and oil consumption because of poor engine break in? All TDI and many modern engines also require synthetic oil. (Ever see oil sludge in a VW/Audi? Not pretty!) If an oil sludge problem develops from not using synthetic oil is it an engine design/build problem, an engine break in problem, or an owner maintenance-oil change problem?
During combustion, the pressures in the engine cylinder spike as the fuel burns. The rings act as a labyrinth seal and seal the piston against the engine cylinder wall and scrape oil. In general, diesel engines see much higher pressures than gasoline engines. A diesel engine may see 2000 psi peak combustion pressure vs. 1000-1700 psi for a gasoline engine. Engine pistons are not perfect round cylinders when cold because they compensate and expand when warm. The pistons also need to heat relax during break in. Before the engine is warmed up or broken in, the pressures of combustion can push past the piston rings more than a fully broken in and warmed up engine. This reduces engine efficiency, power, and fuel mileage but will improve as the engine is broken in and seals better. All engines benefit from a normal warm up during normal operation.
From minute 0, the rings and freshly honed cylinder walls will scrape against each other and begin break in by wearing into each other. Again, your brand new car's engine was already run in at the factory. The friction of the rings against the cylinder walls will also help heat cycle the rings. A good break in would have incremental increases in heat cycling, load, and rpm. The reason why you want to avoid moderate and high load/rpm operation at minute 0 on a cold engine is because this sudden increase generates excessive blow by and oil glazing. It's normal for a light coat of oil to be present on the cylinder walls, even more so during engine break in. But excess heat generated by high rpm/load can cause this oil to flash burn and glaze. Glazing can create generates hot spots where the rings are not yet seated evenly. This glaze is very smooth and prevents proper ring and cylinder break in. Excessive idling and consistently "babying" the engine can create the same problem.
Remember the section above where I wrote "the truth is somewhere in the middle"? I believe that the best engine break in is a moderate break in - not hard but certainly not easy. This means pushing the engine hard enough to seat the rings but not running it too light or too hard and creating glazing. My suggestion is to follow the owner's manual written by the people who made your car.
In the end, remember that anecdotal evidence or small sample sizes do not make a break in method right or wrong. We would all like to believe that individuals hold some special power over their cars that will result in a perfect break in and the best car. The truth is that different cars of the same model will have some engine and powertrain variation, even if everything else is equal. Some cars are lemons from birth and some come off the assembly line in flawless condition. If you still believe in the "hard break in" method, read this MotorTrend article which gets the advice of multiple automotive engineers from Ford, Honda, and GM who discuss the hard engine break in. If you read the popular mythbusting engine break in site, some of the advice is for breaking in an engine on a dyno. On the street it says to run your bike up to only 65 mph. Even if you follow his advice I would bet many overdo it.
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Differences between this and other popular engine break in advice: my suggestions on engine rpm are not so strict because it really depends on the situation. It's hard to quantify power as an exact RPM and load since each situation is slightly different. Instead, I write estimated rpm and % power. Terms like baby the engine, race, and normal driving mean different things to different people so this article gives some rough suggestions. Use your judgment to apply them depending on the situation. Exact mileages for each break in step are also hard to quantify because 10 miles at redline, up a hill, in stop and go driving, is not the same as 10 miles of highway break in.
For example, if you're going downhill in 3rd gear at 40 mph, the engine has little load but higher rpm. This is a case of low % power. But going back up the same hill in 3rd gear at 40 mph, the engine will be at the same rpm but have higher load. Both these situations have different accelerator pedal positions since a different amount of power is requested by the driver. As a general rule during initial break in, medium rpm with medium load is better than low rpm with high load since this can lug the engine which is bad in general. Just remember that a little more or a little less during engine break in isn't as important as long term maintenance on the long term health of the engine. A little more or less during break in won't cause your engine to blow up.
On a brand new engine (rebuilt or replaced engine), let the idle stabilize to build oil pressure, etc.. You should also be checking coolant levels, adjusting idle, or checking other things on a new engine. Once the rebuilt engine checks are complete, drive it with normal load, about 50-60% power until the engine is warm.
On a new car (remember, the engine was run at the factory) and once the engine is warmed up, drive normally with up to 70% power (around 2500-3600 rpm on a VW TDI) during normal driving for the initial break in. You won't kill the engine if you deviate from this so if conditions warrant higher rpm to avoid high load/low rpm (like lugging the engine up a hill), go for it. Don't baby it but don't race it to redline either. As a rough guideline, when on a flat road, keep the rpm moving up and down around 2000-2200 rpm on your TDI. Avoid extended idling.
After you've put some miles on it and once the engine is warm, rev it at varying throttle up to about 75-80% with medium load while driving in stop and go conditions. You want to avoid low rpm/high load power settings (like lugging the engine) so don't be afraid to downshift. Avoid steady rpm driving (like highway) and excessive idling. The best thing you can do is to drive up to 75-80% power and then coast down in gear under engine braking (foot completely off the accelerator pedal) in smooth, gradual cycles. This heats up the engine and then lets it cool down. Remember, there are oil spray jets in your turbodiesel (and most turbocharged cars) that spray the underside of the engine pistons to cool them down. Driving with moderate load and then letting it coast down in gear will heat cycle the engine. This is much easier on a manual transmission car.
If it's a rebuilt engine, change the oil at your discretion. A rough suggestion is after 1-2 miles and again at 5-10 miles. If this is a new car from the dealer, follow the recommended service/oil change in your owner's manual. I do not suggest changing the engine oil at an earlier mileage than the factory suggestion. Most engines already had the first oil change at the factory. Remember, dealers are independently operated so I suggest following the factory's suggestion, not the dealer's suggestion. All new TDI use VW spec 507.00 engine oil so make sure the dealer uses only VW 507.00 for warranty purposes.
Repeat the above for the first 500 miles, gradually increasing the load/rpm cycles of the engine. Between about 500-1000 miles, drive more normally. A brief, smooth, rpm cycling to full power is fine after 1000 miles. Don't jam the accelerator pedal but don't be afraid to press it all the way down either. You still want to avoid the use of cruise control or steady rpm driving. If this is a rebuilt engine, change the oil at your discretion.
Once you exceed well over 1000 miles, you can drive normally after warm up. You even want to rev it to redline under moderate load a few times to finish relaxing and heat cycling the engine. This is not the "hard break in" method that encourages high load and high revving from hour 0 (brand new engine). Always let the engine warm up with low load driving before higher rpm operation. This is the difference between the "hard" break in and proper break in: varying the rpm between low and high rpm and load on a warm engine is not the same as the hard break in method of high load and rpm on a cold engine - NEVER do that, even after engine break in. Avoid the use of cruise control or steady rpm driving, although by this point it's not as critical as from hour 0.
Once you exceed 5000 miles, most of the initial break in has occurred. Any engine oil consumption should go down and fuel economy should slowly increase. You still want to vary the speed when you can, but it's not as critical as before.
Past 10,000 miles, most of the engine break in has occurred on a diesel but your compression, oil consumption, and fuel mileage may still improve slightly to 25,000-50,000 miles. Engine oil analysis shows that even gasoline engines are still slightly breaking in slightly at over 10,000 miles. From now on, avoid lugging the engine, try to regularly drive at moderate power, and occasionally rev the engine under sustained high load/rpm. This helps to clear soot in the exhaust out of the turbo by raising exhaust gas temperatures and burning the soot up and blowing it out, especially for cars with VNT turbos. Even with a gasoline car, going to occasional sustained high load/rpm will help burn up engine deposits.
Any engine works best at its normal operating temperature so from now on, drive under low-medium power until it's warmed up.
Engine lifespan and condition is more about consistency, maintenance, and long term habits (and engine build/design quality which is out of your control) than a secret technique that will give you some competitive edge. Anecdotal evidence or small sample sizes do not make a break in method right or wrong. People like to believe in a story or that their car is special and in a way, it is special. Variations in engine build tolerances, overall build quality, if the guy on the assembly line wasn't paying attention, all make your car unique and produce variances in power, fuel economy, and engine compression. Every car and every engine that comes off the assembly line has some variance. If a secret engine break in technique gave extra power, why don't hand built Corvette Z06 engines or Ferrari engines get this treatment? Surely Ferrari can add it to the cost of a $250,000 (before dealer markup) car! Every Nissan GTR is broken in on a bench dynamometer for 44 minutes including up to redline. After the engine is in the car it's dyno tested again and then driven hard on a track by a factory test driver (where they also do brake and transmission testing) so any "hour 0" break in technique by the owner is moot. Does this mean a hard engine break in is factory recommended for that car or that it doesn't make a difference over the long term? If engine break in was the determining factor in car life, wouldn't that make well beaten used rental cars the best cars ever?
Even if you didn't follow the optimum engine break in techniques, consistent engine warm up and consistent maintenance contribute to a long engine life span. Letting a 3 year old child have a soda won't contribute to obesity but giving them 2 liters of soda every day for life will. In the end, almost all original owners of passenger cars get rid of the car before they need a new engine due to wear, so does it make a difference anyways?
For info on the new 2012+ Passat TDI, see 1000q: b7 Passat TDI guide
For info on the new style 2011+ VW Jetta TDI, see 1000q: mk6 VW Jetta TDI guide
For checklist and FAQ on the 2010+ VW Golf TDI, see 1000q: VW Golf new owner guide
For FAQ and info on the 2010-12 Audi A3 TDI, see 1000q: Audi A3 TDI checklist
For exclusive info on the new 2011+ VW Touareg TDI, see 1000q: 2011 VW Touareg TDI guide.