I have seen many threads on here with people achieving high miles on their engines. The leader at the moment is at 350K [https://www.thenewx.org/forum/9-general-xterra/88585-top-mileage-thread-lead-350-000-a.html], which is astoundingly impressive. On the flip side, I ran across a site that had the following to say about the VQ40DE Engine Service Life:
I would like to get people's opinions regarding whether they think the engine life expectancy of 200K is accurate or overly conservative. Also, what do people think about the timing chain service life being 150K? I have seen timing chain kits that include new chains and other parts. Is this something that should be considered a maintenance item or is it better not to open up the engine and just keep the oil changed regularly with a quality synthetic? Lastly, what is meant by the valve clearance needing to be adjusted every 60K? I've never even heard of that before.The engine has three timing chains, their service life is about 150,000 miles of mileage (200,000-250,000 km). The valve clearance needs to be adjusted every 60,000 miles of mileage (90,000 km). The Nissan VQ40DE life expectancy is 200,000 miles of mileage (300,000 km).