Two-Thirds of Earliest Tesla Drivetrains To Fail In 60,000 Miles, Owner Data Suggests

Photo: terren | Flickr

With almost 100,000 on the world’s roads, the Tesla Model S electric car is a remarkable achievement.

It remains the longest-range electric car in volume production more than three years after it launched.

But reliability issues with electric traction motors in early cars–those from the 2012 and 2013 model years–have dogged the earliest owners.

Now, a new analysis of data provided to Plug-In America by 327 owners of early Tesla Model S cars suggests that as many as two-thirds of those early Model S drivetrains will need to be replaced within 60,000 miles.

This analysis has not been publicly disclosed before now. Before publishing this story, Green Car Reports asked several specific questions of Tesla Motors to help put the analysis in context.

Tesla declined to answer those questions. Instead, it issued general statements about its reliability. Both the questions and its statement are at the end of the article.

2013 Tesla Model S owned by David Noland, Catskill Mountains, NY, Oct 2015

Reliability: really a liability?

Since Consumer Reports dropped the Tesla Model S from its list of recommended buys due to a“worse-than-average overall problem rate”, the barbs between the company’s supporters and detractors have only sharpened.

At issue is the significance, if any, of Consumer Reports’ findings. Given that Mercedes-Benz–another highly successful luxury brand–also gets a worse-than-average rating, does it really matter? And should one also consider TrueDelta’s more pessimistic assessment?

Do a drive experience rated at “103 out of 100” points and 97-percent customer satisfaction mean Tesla has little to worry about? Or do lengthening waiting times at service centers foreshadow a fall in customer loyalty and brand prestige?

Without the proper context, it all reduces to an electric-vehicle version of the fable about the blind men and the elephant.

But there’s a trove of statistics that can contribute to the conversation. And a Weibull analysis of that data suggests that two-thirds of early (2012 and 2013) Model S cars can expect a drivetrain failure within 60,000 miles.

Tesla Model S electric motor and drive unit [photo posted by user Tam to Tesla Motors forum]

That’s troubling.

Clearly, Tesla’s eight-year warranty coverage on the drivetrain protects new and used buyers. And the company has said several times that it has made great leaps in quality as it gains experience in building the car.

Tesla’s November update said the company has cut its failure rates by half, while CEO Elon Musk has expressed strong confidence in the improved drivetrains it has been shipping in recent months.

But the data set used to analyze drivetrain reliability includes about 10 times as many early (2012 and 2013) cars as recent ones from the 2014 and 2015 model years.

If enough recent buyers add their information, we may be able to improve the analysis and get statistical backup for the trend of improved reliability Tesla has mentioned.

Plug-In America’s big (enough) data

The failure estimates above come from an analysis on data from Plug in America’s survey of Tesla Model S vehicles. Links at the bottom of the PIA page allow the data set to be downloaded.

In the survey, respondents provided a variety of information on their Model S ownership experience, including total miles driven, whether they’ve had a motor swap (drivetrain replacement), and if so, what the odometer reading was at the time.

In October, when this analysis was run, the data set had 370 respondents. Not having any reliability software handy, I asked a reliability engineer to crunch the numbers–and received the startling reply that the “characteristic life” of the drive train was about 50,000 miles.

In a reliability context, the so-called characteristic life is the age at which 63.2 percent of parts are expected to fail. This represents a survival rate of 36.8 percent, or 0.368. That value is the inverse of e, the base of the natural logarithm. In math terms, 1/e = ½.718 = 0.368.

Weibull Analysis of earliest 2012-2013 Tesla Model S drivetrains [plotted by Matthew Klippenstein]