Real-World Reliability Data
The Long-Term Quality Index is a collaborative project between Steve Lang and Nick Lariviere, designed to give the average car buyer a picture of what the long-term reliability of different makes and models based on real-world used vehicle data.
This site is still a work in progress. While we aim to provide objective analysis, we also understand there is no absolute method to predict a vehicle's quality level with certainty(ie: your mileage may vary).
The aim of this site isn't to say "you should buy vehicle X, and not vehicle Y" but rather to provide an object way to compare different vehicles based on reliability data collected from trade-in vehicles. The focus of this data, and our analysis, is centered on powertrain(engine/transmission) issues, and the distribution of vehicles based on mileage. Some charts refer to "engine" issues, "transmission" issues and "powertrain" issues individually; in these cases "powertrain" refers to either engine or transmission issues(ie: a vehicle that has both engine and transmission issues, it will only be counted once under powertrain, and will be included in both the engine and transmission charts).
Mileage distribution charts are designed to give you an idea about what the average life-span of a vehicle is, based on the trade-in vehicle data we have. Obviously there is some selection bias here; if someone buys a vehicle and keeps it until it croaks, it won't show up in our data. However, with over 300,000 vehicles(and counting), and by taking measures to ensure our analysis isn't unduly influenced by outliers, we're able to give a general picture of what the 'average' vehicles for a specific model will look like.
In these mileage charts, the blue curve with the darker background represents the average distribution of vehicles(across all makes and models in our database). Many models have a similar distribution of vehicles, which represents a normal distribution of vehicles(most vehicles are in the middle range of mileage, between 120,000 and 180,000 miles). Some vehicles have a similar shape, but are positioned farther to the right or left than the typical distribution, which represents either a larger distribution of low-mileage vehicles(farther to the left), or higher-mileage vehicles(farther to the right). Newer models will obviously have most of their vehicles with low miles, while defunct models will generally have higher-mileage vehicles. Generally(but not always), a heavy concentration of vehicles in one area(a peak on the curve) is an indication of issues with that model.
You may also find some of the information in our Frequently Asked Questions useful.
For further reading, particularly about finding and buying used vehicles, please see some of Steve Lang's articles on the subject: