I think a lot of people want to compare ALL diesels to some big, OTR trucks. If we were to just stick with Volkswagen or similar light duty automotive applications, for the most part the diesel has no real longevity advantage. Because the engine family (in the VAG world, anyways) on which diesels are based, are also found in gasoline trim.
If you stripped them down to the bare block, you'd be hard pressed to tell any difference. The diesel will have chunkier rods... they have to, they have ~ twice the compression ratio. The older (pre-TDI) VAG diesels were not very powerful, so they had to be geared lower, which meant they had to reciprocating friction advantage. The TDIs, however, make a significant amount more torque than most comparable gasoline engines, so they are geared higher. Which means they DO have a slight advantage. Over time, an engine that needs 2500 RPM to hold 80 MPH will have less wear than an engine that needs 3000 RPM to do the same. But how much does that difference really make? Chances are, no normal humans will dare keep a car long enough to truly find out. In a case like that, the diesel may go to 1,000,000 miles to show the same wear that the gasser would show at 800,000 miles. But who drives ANY car that much anyways?
Generally speaking, Volkswagen's gasoline engines are very good regarding wear. There are some that have some piston ring issues, and others that have some chain issues. But in general, with good care, they'll easily last as long as the car they are bolted into.
I just bought a 2004 Passat, AWM engine (1.8t), that is nearing 200k miles. I've cared for it since it was new. I've done every single service to it, with the correct 502.00 spec 5w40 oil, and the big Mann oil filters. Its engine uses very little oil, leaks no oil, and sounds and runs as good as new. This is an engine that is very often cited for being problematic, too. Just goes to show that if cared for properly, even an engine that has a troublesome track record can still buck the trend.
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