Reader Question: TDI Diesel Longevity?

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Here’s the latest reader question, along with my reply!

Steve asks: Eric, you have clearly stated your position that turbocharging an everyday car is a bad practice because it increases the stresses on many engine components and thereby reduces the engine life. My question: is this also true of diesels? It seems to me that a diesel engine is inherently a sturdy beast and was designed from the get-go to be turbocharged, so the boost shouldn’t be detrimental to the longevity of the engine.  Agree?  I own a 2015 VW Golf Sportwagen TDI, so the question is not just academic to me.

My reply: Yes, agreed! And here’s why: It’s not just that diesel engines are built tougher – use heavier duty blocks and other components. It is because they are diesels and they operate differently than a gas-burning (and spark-ignition) engine. They are low-RPM engines (most “redline” well before 4,500 RPM and most rarely need to be revved much beyond 3,500 RPM. Gas engines routinely rev twice as fast – and often. This multiplies the force applied to the reciprocating assembly.

Diesels also burn diesel, which is both a fuel and a lubricant, unlike gas – which is a fuel and a solvent. Gas washes lubrication off of wear-critical parts; diesel helps keep them from wearing.

Diesels usually last much longer than gas-burning engines. I would expect the same to be the case with your VW TDI!

Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!

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  1. Diesels have a compression ratio of 22:1, which is why they have a heavier and sturdier block and heads. And why they are fuel injected. Diesels also vary the amount of air while maintaining a constant fuel injection, regardless of speed. Am I correct on this last point?

    • You have that backwards. Diesels have no throttle butterfly – they always ingest all the air that they can, and they control power by injecting the correct amount of fuel. It’s why they run extremely lean sometimes and make high NOx emissions.