Bionic Man wrote:
I'm interested in this. It isn't that I don't trust you, but where do you find documentation that all vehicles under 8500 pounds are validated to 150k miles? Is that the "medium duty" spec comes in?
It's not an SAE standard. From what I've been able to piece together, CARB was the organization that originally designated a 150,000 validated-design life. As CARB emissions were generally adopted for all 50 states, it meant all automakers had to validate their vehicles to that lifespan. It's not just coincidence that every light car has a maintenance schedule that goes to 150,000 miles. Can an automaker design for longer? Sure. But there's not widespread
validation beyond that number (validation doesn't necessary equal design life). Ford went way longer with the EcoBoost validation tests, but it was mostly for proof-of-concept as it was a dramatic departure from traditional powertrains.
For some of the other poster's questions... Yes, they do validate under extreme conditions. Doing things like simulating a full load at -40F, then shocking the system to extreme hot ambient environments. Many of the specific test they perform are well beyond what the typical buyer would ever encounter. I watched an F150 driveline on a dyno, where it was started up, then suddenly stopped. Over and over for weeks. To simulated a "life-time" of somebody throwing it into park while rolling. Or having a driver to a figure 8 with curbs across each quadrant, to simulate a lifetime of sidewalk hopping (commercial and EMS vehicles only for this test). Of course, some of those extreme validation tests miss real world conditions, like super short grocery store runs causing condensation buildup in the original EcoBoost's intercooler, causing hiccups when it finally got enough boost to ingest that condensate.
When they publish maintenance schedules, it's developed using these validation tests (developed with computer simulations), based on failures experienced, combined with some statistics and wizardry. If a component is listed needing replacement in the maintenance schedule, it's been validated to that mileage. If its not listed (timing chain, for example) it means they did not experience a statistically valid failure during validation. Of course, that doesn't mean infinite lift either. But you're own your own to figure it out. Besides costs, extending validation testing would increase model development time, which for light vehicles tends to be very short.
Medium-Duty test cycles are longer. The OEMs each decide what their design life will be, designated as B(x), where x is the number of vehicles experiencing a major failure. The numbers are generally available to fleet buyers, but rarely published in consumer material.
