A car dealer's scientific guide to the most durable used cars

Everybody wants to own a keeper. A car that provides so much personal satisfaction that the years and miles can just fly by, while the enduring qualities of that daily driver remain picture perfect.

The hard part for most folks comes down to hype.

To sell more cars, manufacturers continue to promote short-term quality studies that have little or nothing to do with the long-term ownership experience. For example, J.D. Power's Initial Quality Study only covers the first 90 days of ownership, while its long-term survey tracks three-year-old vehicles over a short 12 month span.

In a market where the average car and truck is now over 11 years old, a long-term reliability study requires a much longer view of car ownership. For those of us who are looking to find a good used car, or even feel concerned about how a new car will hold up, we should be able to know the longevity of a vehicle for the entire life cycle instead of just a random early point in time.

This is why Nick Lariviere and myself have developed the Long-Term Quality Index. With over 550,000 data samples from all over the country, we have been able to look specifically at measuring the three key ingredients that tell you how well a given model has performed in today's marketplace; mileage, age and condition.

To make this study fair and impartial, we have also taken two unique steps that represent a first for long-term reliability studies in the auto industry. The first is removing owner bias. Certain people will always recommend a car simply because that's what they bought in the past and if something bad happens, they won’t tell you about it. Others are just oblivious to the thumping of a bad transmission, or the knocking of a bad motor. That is why we only have mechanics and skilled professionals appraise the vehicle’s condition.

Second, we focus exclusively on condition and longevity. Cars that are either 18 years or older, or have 180,000 or more miles, have endured well past the average life-span of the average vehicle.

In our study, we're finding that only a chosen few can routinely achieve these two levels of longevity without a major mechanical defect. It's this level of engineering excellence that we want to highlight in our study.

So what have we found so far? Some of what you might expect, but a lot of surprises.

The Over-300,000 Club Is Still Pretty Exclusive: Five types of vehicles make up more than 60% of the cars and trucks with at least 300,000 miles. They are:

• GM full-sized trucks and SUVs

• Ford full-sized trucks and SUVs

• Ford rear-wheel-drive V-8 cars

• Honda four-cylinder cars

• Toyota everything (except Celica and RAV4)